2024-03-28T12:37:47Z
http://quanta.ws/ojs/index.php/quanta/oai
oai:ojs.quanta.ws:article/17
2024-02-05T10:31:25Z
quanta:ART
A Career of Unyielding Exploration: In Memory of Ion C. Baianu (1947-2013)
Brown, Ronald
Glazebrook, James F.
We were deeply saddened to learn of the sudden death of our colleague, friend, and member of the Editorial Board of Quanta, Professor Ion C. Baianu, who unexpectedly passed away in Urbana, Illinois, USA, on February 10, 2013. Ion left behind his wife, Kimiko, his son, Stephen, and daughters, Antonia and Christina. He also left behind the achievements of a profound and illustrious career in his chosen fields of biophysics, spectroscopy, food science, and bioengineering.Quanta 2013; 2: 1–6.
Quanta
2013-05-15
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
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http://quanta.ws/ojs/index.php/quanta/article/view/17
10.12743/quanta.v2i1.17
Quanta; Vol 2, No 1 (2013); 1-6
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/17/67
oai:ojs.quanta.ws:article/44
2024-02-05T10:32:07Z
quanta:ART
Accommodating Retrocausality with Free Will
Aharonov, Yakir
Cohen, Eliahu
Shushi, Tomer
Retrocausal models of quantum mechanics add further weight to the conflict between causality and the possible existence of free will. We analyze a simple closed causal loop ensuing from the interaction between two systems with opposing thermodynamic time arrows, such that each system can forecast future events for the other. The loop is avoided by the fact that the choice to abort an event thus forecasted leads to the destruction of the forecaster's past. Physical law therefore enables prophecy of future events only as long as this prophecy is not revealed to a free agent who can otherwise render it false. This resolution is demonstrated on an earlier finding derived from the two-state vector formalism, where a weak measurement's outcome anticipates a future choice, yet this anticipation becomes apparent only after the choice has been actually made. To quantify this assertion, weak information is described in terms of Fisher information. We conclude that an already existing future does not exclude free will nor invoke causal paradoxes. On the quantum level, particles can be thought of as weakly interacting according to their past and future states, but causality remains intact as long as the future is masked by quantum indeterminism.Quanta 2016; 5: 53–60.
Quanta
Israel Science Foundation Grant No. 1311/14
ERC-AD NLST
ICORE Excellence Center "Circle of Light"
2016-01-10
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/44
10.12743/quanta.v5i1.44
Quanta; Vol 5, No 1 (2016); 53-60
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/44/80
Copyright (c) 2016 Quanta
oai:ojs.quanta.ws:article/69
2024-02-05T10:32:35Z
quanta:ART
On Schmidt Decomposition: Approach Based on Correlation Operator as Bipartite Entanglement Entity
Herbut, Fedor
An elaborated review with proofs of Schmidt canonical decomposition of any bipartite state vector is approached through general subsystem basis expansion. The upgraded forms of Schmidt decomposition in terms of correlation operator and twin observables are presented in detail. The discussion is extended to distant measurement, Einstein–Podolsky–Rosen states and Schrödinger's steering. All claims and proofs are given in standard form unlike in the previous articles of the author where all results were obtained utilizing the very rarely used antilinear Hilbert–Schmidt maps of one subsystem state space into the other. For practical reasons the formalism of partial traces with their rules and reduced density operators together with correlation operator are used.Quanta 2018; 7: 19–39.
Quanta
2018-02-20
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/69
10.12743/quanta.v7i1.69
Quanta; Vol 7, No 1 (2018); 19-39
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/69/105
Copyright (c) 2018 Quanta
oai:ojs.quanta.ws:article/119
2024-02-05T10:32:57Z
quanta:ART
Impossibility of Distinguishing Two Preparations for a Pure State from No-signaling
Pati, Arun K.
A pure state of a physical system can be prepared in an infinite number of ways. Quantum theory dictates that given a pure state of a physical system it is impossible to distinguish two preparation procedures. Here, we show that the impossibility of distinguishing two preparation procedures for the same pure state follows from the no-signaling principle. Extending this result for a pure bipartite entangled state entails that the impossibility of distinguishing two preparation procedures for a mixed state follows from the impossibility of distinguishing two preparations for a pure bipartite state.Quanta 2020; 9: 16–21.
Quanta
2020-10-22
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/119
10.12743/quanta.v9i1.119
Quanta; Vol 9, No 1 (2020); 16-21
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/119/125
Copyright (c) 2020 Quanta
oai:ojs.quanta.ws:article/167
2024-02-05T10:33:21Z
quanta:ART
Steady State in Ultrastrong Coupling Regime: Expansion and First Orders
Latune, Camille Lombard
Understanding better the dynamics and steady states of systems strongly coupled to thermal baths is a great theoretical challenge with promising applications in several fields of quantum technologies. Among several strategies to gain access to the steady state, one consists in obtaining approximate expressions of the mean force Gibbs state, the reduced state of the global system-bath thermal state, largely credited to be the steady state. Here, we present analytical expressions of corrective terms to the ultrastrong coupling limit of the mean force Gibbs state, which has been recently derived. We find that the first order term precisely coincides with the first order correction obtained from a dynamical approach—master equation in the strong-decoherence regime. This strengthens the identification of the reduced steady state with the mean force Gibbs state. Additionally, we also compare our expressions with another recent result obtained from a high temperature expansion of the mean force Gibbs state. We observe numerically a good agreement for ultra strong coupling as well as for high temperatures. This confirms the validity of all these results. In particular, we show that, in term of coherences, all three results allow one to sketch the transition from ultrastrong coupling to weak coupling.Quanta 2022; 11: 53–71.
Quanta
2022-11-19
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/167
10.12743/quanta.v11i1.167
Quanta; Vol 11, No 1 (2022); 53-71
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/167/151
Copyright (c) 2022 Quanta
oai:ojs.quanta.ws:article/8
2024-02-05T10:30:58Z
quanta:ART
Popper's Experiment: A Modern Perspective
Qureshi, Tabish
Karl Popper had proposed an experiment to test the standard interpretation of quantum mechanics. The proposal survived for many year in the midst of no clear consensus on what results it would yield. The experiment was realized by Kim and Shih in 1999, and the apparently surprising result led to lot of debate. We review Popper's proposal and its realization in the light of current era when entanglement has been well studied, both theoretically and experimentally. We show that the "ghost-diffraction" experiment, carried out in a different context, conclusively resolves the controversy surrounding Popper's experiment.Quanta 2012; 1: 19–32.
Quanta
2012-11-15
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/3
10.12743/quanta.v1i1.8
Quanta; Vol 1, No 1 (2012); 19-32
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/3/64
oai:ojs.quanta.ws:article/26
2024-02-05T10:31:41Z
quanta:ART
On Unitary Evolution and Collapse in Quantum Mechanics
Giacosa, Francesco
In the framework of an interference setup in which only two outcomes are possible (such as in the case of a Mach–Zehnder interferometer), we discuss in a simple and pedagogical way the difference between a standard, unitary quantum mechanical evolution and the existence of a real collapse of the wavefunction. This is a central and not-yet resolved question of quantum mechanics and indeed of quantum field theory as well. Moreover, we also present the Elitzur–Vaidman bomb, the delayed choice experiment, and the effect of decoherence. In the end, we propose two simple experiments to visualize decoherence and to test the role of an entangled particle.Quanta 2014; 3: 156–170.
Quanta
2014-11-27
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/26
10.12743/quanta.v3i1.26
Quanta; Vol 3, No 1 (2014); 156-170
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/26/92
Copyright (c) 2014 Quanta
oai:ojs.quanta.ws:article/64
2024-02-05T10:32:20Z
quanta:ART
Schrödinger's Cat: Where Does The Entanglement Come From?
Ionicioiu, Radu
Schrödinger's cat is one of the most striking paradoxes of quantum mechanics that reveals the counterintuitive aspects of the microscopic world. Here, I discuss the paradox in the framework of quantum information. Using a quantum networks formalism, I analyse the information flow between the atom and the cat. This reveals that the atom and the cat are connected only through a classical information channel: the detector clicks → the poison is released → the cat is killed. No amount of local operations and classical communication can entangle the atom and the cat, which are initially in a separable state. This casts a new light on the paradox.Quanta 2017; 6: 57–60.
Quanta
Romanian Ministry of Research and Innovation
2017-10-06
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/64
10.12743/quanta.v6i1.64
Quanta; Vol 6, No 1 (2017); 57-60
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/64/97
Copyright (c) 2017 Quanta
oai:ojs.quanta.ws:article/86
2024-02-05T10:32:46Z
quanta:ART
Environmental Effects on Nonlocal Correlations
Guha, Tamal
Bhattacharya, Bihalan
Das, Debarshi
Bhattacharya, Some Sankar
Mukherjee, Amit
Roy, Arup
Mukherjee, Kaushiki
Ganguly, Nirman
Majumdar, Archan S.
Environmental interactions are ubiquitous in practical instances of any quantum information processing protocol. The interaction results in depletion of various quantum resources and even complete loss in numerous situations. Nonlocality, which is one particular quantum resource marking a significant departure of quantum mechanics from classical mechanics, meets the same fate. In the present work we study the decay in nonlocality to the extent of the output state admitting a local hidden state model. Using some fundamental quantum channels we also demonstrate the complete decay in the resources in the purview of the Bell–Clauser–Horne–Shimony–Holt inequality and a three-settings steering inequality. We also obtain bounds on the parameter of the depolarizing map for which it becomes steerability breaking pertaining to a general class of two qubit states.Quanta 2019; 8: 57–67.
Quanta
Government of India: DST-INSPIRE
University Grants Commission (UGC)
Project no. DST/ICPS/Qust/2018/98 of Department of Science and Technology
Research Initiation Grant of BITS-Pilani, Hyderabad vide letter no. BITS/GAU/RIG/2019/H0680
2019-10-28
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/86
10.12743/quanta.v8i1.86
Quanta; Vol 8, No 1 (2019); 57-67
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/86/119
Copyright (c) 2019 Quanta
oai:ojs.quanta.ws:article/180
2024-02-05T10:33:21Z
quanta:ART
Jordan in The Church of The Higher Hilbert Space: Entanglement and Thermal Fluctuations
Vedral, Vlatko
I revisit Jordan's derivation of Einstein's formula for energy fluctuations in the black body in thermal equilibrium. This formula is usually taken to represent the unification of the wave and the particle aspects of the electromagnetic field since the fluctuations can be shown to be the sum of wave-like and particle-like contributions. However, in Jordan's treatment there is no mention of the Planck distribution and all averages are performed with respect to pure number states of radiation (mixed states had not yet been discovered!). The chief reason why Jordan does reproduce Einstein's result despite not using thermal states of radiation is that he focuses on fluctuations in a small (compared to the whole) volume of the black body. The state of radiation in a small volume is highly entangled to the rest of the black body which leads to the correct fluctuations even though the overall state might, in fact, be assumed to be pure (i.e. at zero temperature). I present a simple derivation of the fluctuations formula as an instance of mixed states being reductions of higher level pure states, a representation that is affectionately known as "Church of the Higher Hilbert Space". According to this view of mixed states, temperature is nothing but the amount of entanglement between the system and its environment.Quanta 2022; 11: 1–4.
Quanta
National Research Foundation, Singapore
Ministry of Education, Singapore
Wolfson College, University of Oxford, United Kingdom
2022-03-20
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/180
10.12743/quanta.v11i1.180
Quanta; Vol 11, No 1 (2022); 1-4
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/180/145
Copyright (c) 2022 Quanta
oai:ojs.quanta.ws:article/249
2024-02-05T10:33:31Z
quanta:ART
On Weak Values and Feynman's Blind Alley
Sokolovski, Dmitri
Feynman famously recommended accepting the basic principles of quantum mechanics without trying to guess the machinery behind the law. One of the corollaries of the Uncertainty Principle is that the knowledge of probability amplitudes does not allow one to make meaningful statements about the past of an unobserved quantum system. A particular type of reasoning, based on weak values, appears to do just that. Has Feynman been proven wrong by the more recent developments? Most likely not.Quanta 2023; 12: 180–189.
Quanta
2023-11-19
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/249
10.12743/quanta.v12i1.249
Quanta; Vol 12, No 1 (2023); 180-189
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/249/166
Copyright (c) 2023 Quanta
oai:ojs.quanta.ws:article/23
2024-02-05T10:31:41Z
quanta:ART
Exploring Quantum, Classical and Semi-Classical Chaos in the Stadium Billiard
King, Chris C.
This paper explores quantum and classical chaos in the stadium billiard using Matlab simulations to investigate the behavior of wave functions in the stadium and the corresponding classical orbits believed to underlie wave function scarring. The simulations use three complementary methods. The quantum wave functions are modeled using a cellular automaton simulating a Hamiltonian wave function with discrete (square pixel) boundary conditions approaching the stadium in the classical limit. The classical orbits are computed by solving the reflection equations at the classical boundary thus giving direct insights into the wave functions and eigenstates of the quantum stadium. Finally, a simplified semi-classical algorithm is developed to show the comparison between this and the quantum wave function method.Quanta 2014; 3: 16–31.
Quanta
2014-01-15
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/23
10.12743/quanta.v3i1.23
Quanta; Vol 3, No 1 (2014); 16-31
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/23/94
http://quanta.ws/ojs/index.php/quanta/article/downloadSuppFile/23/20
http://quanta.ws/ojs/index.php/quanta/article/downloadSuppFile/23/21
http://quanta.ws/ojs/index.php/quanta/article/downloadSuppFile/23/22
http://quanta.ws/ojs/index.php/quanta/article/downloadSuppFile/23/23
http://quanta.ws/ojs/index.php/quanta/article/downloadSuppFile/23/24
http://quanta.ws/ojs/index.php/quanta/article/downloadSuppFile/23/25
oai:ojs.quanta.ws:article/51
2024-02-05T10:32:07Z
quanta:ART
Holism and Time Symmetry
Lewis, Peter J.
Quantum mechanics is often taken to entail holism. I examine the arguments for this claim, and find that although there is no general argument from the structure of quantum mechanics to holism, there are specific arguments for holism available within the three main realist interpretations (Bohm, Ghirardi-Rimini-Weber and many-worlds). However, Evans, Price and Wharton's sideways Einstein-Podolsky-Rosen-Bell example challenges the holistic conclusion. I show how the symmetry between the sideways and standard Einstein-Podolsky-Rosen-Bell set-ups can be used to argue against holism. I evaluate the prospects for extending this insight to more general quantum systems, with a view to producing a genuinely time-symmetric hidden variable theory. I conclude that, although this extension undermines the analogy between the sideways and standard cases, quantum mechanics without holism remains a live possibility.Quanta 2016; 5: 85–92.
Quanta
2016-11-16
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/51
10.12743/quanta.v5i1.51
Quanta; Vol 5, No 1 (2016); 85-92
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/51/82
Copyright (c) 2016 Quanta
oai:ojs.quanta.ws:article/85
2024-02-05T10:32:46Z
quanta:ART
Latent Complete-Lattice Structure of Hilbert-Space Projectors
Herbut, Fedor
To uncover the hidden complete-lattice structure of Hilbert-space projectors, which is not seen by the operator operations and relations (algebraically), resort is taken to the ranges of projectors (to subspaces—to geometry). Taking the range of a projector is completed into a bijection of all projectors onto all subspaces of any finite or countably infinite dimensional Hilbert space. As a second step, this basic bijection is upgraded into an isomorphism of partially ordered sets utilizing the sub-projector relation on the one hand, and the subspace relation on the other. As a third and final step, the basic bijection is further upgraded to isomorphism of complete lattices. The complete-lattice structure is derived for subspaces, then, using the basic bijection, it is transferred to the set of all projectors. Some consequences in the quantum-mechanical formalism are examined with particular attention to the infinite sums appearing in spectral decompositions of discrete self-adjoint operators with infinite spectra.Quanta 2019; 8: 1–10.
Quanta
2019-03-01
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/85
10.12743/quanta.v8i1.85
Quanta; Vol 8, No 1 (2019); 1-10
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/85/114
Copyright (c) 2019 Quanta
oai:ojs.quanta.ws:article/165
2024-02-05T10:33:10Z
quanta:ART
Canonical Structure of A and B Maps
Sudha, Sudha
Karthik, B. N.
Usha Devi, A. R.
Rajagopal, A. K.
In their seminal 1961 paper, Sudarshan, Mathews and Rau investigated properties of the dynamical A and B maps acting on n-dimensional quantum systems. The nature of dynamical maps in open quantum system evolutions has attracted great deal of attention in the later years. However, the novel paper on the A and B dynamical maps has not received its due attention. In this tutorial article, we review the properties of A and B forms associated with the dynamics of finite dimensional quantum systems. In particular, we investigate a canonical structure associated with the A form and establish its equivalence with the associated B form. We show that the canonical structure of the A form captures the completely positive (not completely positive) nature of the dynamics in a succinct manner. This feature is illustrated through physical examples of qubit channels.Quanta 2021; 10: 34–41.
Quanta
2021-11-03
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/165
10.12743/quanta.v10i1.165
Quanta; Vol 10, No 1 (2021); 34-41
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/165/133
Copyright (c) 2021 Quanta
oai:ojs.quanta.ws:article/233
2024-02-05T10:33:31Z
quanta:ART
A Theory of Quantum Instruments
Gudder, Stan
Until recently, a quantum instrument was defined to be a completely positive operation-valued measure from the set of states on a Hilbert space to itself. In the last few years, this definition has been generalized to such measures between sets of states from different Hilbert spaces called the input and output Hilbert spaces. This article presents a theory of such instruments. Ways that instruments can be combined such as convex combinations, post-processing, sequential products, tensor products and conditioning are studied. We also consider marginal, reduced instruments and how these are used to define coexistence (compatibility) of instruments. Finally, we present a brief introduction to quantum measurement models where the generalization of instruments is essential. Many of the concepts of the theory are illustrated by examples. In particular, we discuss Holevo and Kraus instruments.Quanta 2023; 12: 27–40.
Quanta
2023-06-06
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/233
10.12743/quanta.v12i1.233
Quanta; Vol 12, No 1 (2023); 27-40
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/233/158
Copyright (c) 2023 Quanta
oai:ojs.quanta.ws:article/14
2024-02-05T10:31:25Z
quanta:ART
Introduction to Weak Measurements and Weak Values
Tamir, Boaz
Cohen, Eliahu
We present a short review of the theory of weak measurement. This should serve as a map for the theory and an easy way to get familiar with the main results, problems and paradoxes raised by the theory.Quanta 2013; 2: 7–17.
Quanta
2013-05-15
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/14
10.12743/quanta.v2i1.14
Quanta; Vol 2, No 1 (2013); 7-17
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/14/68
oai:ojs.quanta.ws:article/38
2024-02-05T10:32:07Z
quanta:ART
On the Relation Between Quantum Computational Speedup and Retrocausality
Castagnoli, Giuseppe
We investigate the reason for the quantum speedup (quantum algorithms require fewer computation steps than their classical counterparts). We extend the representation of the quantum algorithm to the process of setting the problem, namely choosing the function computed by the black box. The initial measurement selects a setting at random, Bob (the problem setter) unitarily changes it into the desired one. With reference to the observer dependent quantum states of relational quantum mechanics, this representation is with respect to Bob and any external observer, it cannot be with respect to Alice (the problem solver). It would tell her the function computed by the black box, which to her should be hidden. To Alice, the projection of the quantum state due to the initial measurement is retarded at the end of her problem solving action, so that the algorithm input state remains one of complete ignorance of the setting. By black box computations, she unitarily sends it into the output state that, for each possible setting, encodes the corresponding solution, acquired by the final measurement. Mathematically, we can ascribe to the final measurement the selection of any fraction R of the random outcome of the initial measurement. This projects the input state to Alice on one of lower entropy where she knows the corresponding fraction of the problem setting. Given the appropriate value of R, the quantum algorithm is a sum over classical histories in each of which Alice, knowing in advance one of the R-th parts of the setting, performs the black box computations still required to identify the solution. Given a quantum algorithm, this retrocausality model provides the value of R that explains its speed up; in the major quantum algorithms, R is 1/2 or slightly above it. Conversely, given the problem, R=1/2 always yields the order of magnitude of the number of black box computations required to solve it in an optimal quantum way.Quanta 2016; 5: 34–52.
Quanta
2016-01-10
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/38
10.12743/quanta.v5i1.38
Quanta; Vol 5, No 1 (2016); 34-52
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/38/79
Copyright (c) 2016 Quanta
oai:ojs.quanta.ws:article/76
2024-02-05T10:32:35Z
quanta:ART
Quantum Mechanics and Global Determinism
Adlam, Emily Christine
It is proposed that certain features of quantum mechanics may be perspectival effects, which arise because experiments performed on locally accessible variables can only uncover a certain subset of the correlations exhibited by an underlying deterministic theory. This hypothesis is used to derive the no-signaling principle, thus resolving an open question regarding the apparently fine-tuned nature of quantum correlations. Some potential objections to this approach are then discussed and answered.Quanta 2018; 7: 40–53.
Quanta
2018-07-16
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/76
10.12743/quanta.v7i1.76
Quanta; Vol 7, No 1 (2018); 40-53
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/76/107
Copyright (c) 2018 Quanta
oai:ojs.quanta.ws:article/140
2024-02-05T10:32:57Z
quanta:ART
Some Remarks on the Entanglement Number
Androulakis, George
McGaha, Ryan
Gudder, in a recent paper, defined a candidate entanglement measure which is called the entanglement number. The entanglement number is first defined on pure states and then it extends to mixed states by the convex roof construction. In Gudder's article it was left as an open problem to show that Optimal Pure State Ensembles (OPSE) exist for the convex roof extension of the entanglement number from pure to mixed states. We answer Gudder's question in the affirmative, and therefore we obtain that the entanglement number vanishes only on the separable states. More generally we show that OPSE exist for the convex roof extension of any function that is norm continuous on the pure states of a finite dimensional Hilbert space. Further we prove that the entanglement number is an LOCC monotone, (and thus an entanglement measure), by using a criterion that was developed by Vidal in 2000. We present a simplified proof of Vidal's result where moreover we use an interesting point of view of tree representations for LOCC communications. Lastly, we generalize Gudder's entanglement number by producing a monotonic family of entanglement measures which converge in a natural way to the entropy of entanglement.Quanta 2020; 9: 22–36.
Quanta
2020-12-11
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/140
10.12743/quanta.v9i1.140
Quanta; Vol 9, No 1 (2020); 22-36
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/140/126
Copyright (c) 2020 Quanta
oai:ojs.quanta.ws:article/206
2024-02-05T10:33:21Z
quanta:ART
The Physical Meaning of the Holographic Principle
Fields, Chris
Glazebrook, James F.
Marciano, Antonino
We show in this pedagogical review that far from being an apparent law of physics that stands by itself, the holographic principle is a straightforward consequence of the quantum information theory of separable systems. It provides a basis for the theories of measurement, time, and scattering. Utilizing the notion of holographic screens, which are information encoding boundaries between physical subsystems, we demonstrate that the physical interaction is an information exchange during which information is strictly conserved. Then we use generalized holographic principle in order to flesh out a fully-general quantum theory of measurement in which the measurement produces finite-resolution, classical outcomes. Further, we show that the measurements are given meaning by quantum reference frames and sequential measurements induce topological quantum field theories. Finally, we discuss principles equivalent to the holographic principle, including Markov blankets and the free-energy principle in biology, multiple realizability and virtual machines in computer science, and active inference and interface theories in cognitive science. This appearance in multiple disciplines suggests that the holographic principle is not just a fundamental principle of physics, but of all of science.Quanta 2022; 11: 72–96.
Quanta
2022-11-21
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/206
10.12743/quanta.v11i1.206
Quanta; Vol 11, No 1 (2022); 72-96
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/206/152
Copyright (c) 2022 Quanta
oai:ojs.quanta.ws:article/3
2024-02-05T10:30:58Z
quanta:ART
Problems in the Science and Mathematics of 'The Logic of Scientific Discovery'
Whiting, Alan B.
Professor Sir Karl Popper (1902-1994) was one of the most influential philosophers of science of the twentieth century. However, in his most famous work 'The Logic of Scientific Discovery' he displays troubling misunderstandings of science and mathematics at a basic level. These call into question his conclusions concerning the philosophy of science.Quanta 2012; 1: 13–18.
Quanta
2012-11-15
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/2
10.12743/quanta.v1i1.3
Quanta; Vol 1, No 1 (2012); 13-18
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/2/63
oai:ojs.quanta.ws:article/35
2024-02-05T10:31:55Z
quanta:ART
Complementarity and the Nature of Uncertainty Relations in Einstein–Bohr Recoiling Slit Experiment
Tanimura, Shogo
A model of the Einstein–Bohr recoiling slit experiment is formulated in a fully quantum theoretical setting. In this model, the state and dynamics of a movable wall that has two slits in it, as well as the state of a particle incoming to the two slits, are described by quantum mechanics. Using this model, we analyzed complementarity between exhibiting an interference pattern and distinguishing the particle path. Comparing the Kennard–Robertson type and the Ozawa-type uncertainty relations, we conclude that the uncertainty relation involved in the double-slit experiment is not the Ozawa-type uncertainty relation but the Kennard-type uncertainty relation of the position and the momentum of the double-slit wall. A possible experiment to test the complementarity relation is suggested. It is also argued that various phenomena which occur at the interface of a quantum system and a classical system, including distinguishability, interference, decoherence, quantum eraser, and weak value, can be understood as aspects of entanglement.Quanta 2015; 4: 1–9.
Quanta
Japan Society for the Promotion of Science (JSPS)
2015-07-15
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/35
10.12743/quanta.v4i1.35
Quanta; Vol 4, No 1 (2015); 1-9
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/35/84
Copyright (c) 2015 Quanta
oai:ojs.quanta.ws:article/66
2024-02-05T10:32:20Z
quanta:ART
Hanbury Brown–Twiss Effect with Wave Packets
Qureshi, Tabish
Rizwan, Ushba
The Hanbury Brown–Twiss (HBT) effect, at the quantum level, is essentially an interference of one particle with another, as opposed to interference of a particle with itself. Conventional treatments of identical particles encounter difficulties while dealing with entanglement. A recently introduced label-free approach to indistinguishable particles is described, and is used to analyze the HBT effect. Quantum wave-packets have been used to provide a better understanding of the quantum interpretation of the HBT effect. The effect is demonstrated for two independent particles governed by Bose–Einstein or Fermi–Dirac statistics. The HBT effect is also analyzed for pairs of entangled particles. Surprisingly, entanglement has almost no effect on the interference seen in the HBT effect. In the light of the results, an old quantum optics experiment is reanalyzed, and it is argued that the interference seen in that experiment is not a consequence of non-local correlations between the photons, as is commonly believed.Quanta 2017; 6: 61–69.
Quanta
2017-11-29
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/66
10.12743/quanta.v6i1.66
Quanta; Vol 6, No 1 (2017); 61-69
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/66/98
Copyright (c) 2017 Quanta
oai:ojs.quanta.ws:article/93
2024-02-05T10:32:46Z
quanta:ART
Observability, Unobservability and the Copenhagen Interpretation in Dirac's Methodology of Physics
Oldofredi, Andrea
Esfeld, Michael
Paul Dirac has been undoubtedly one of the central figures of the last century physics, contributing in several and remarkable ways to the development of quantum mechanics; he was also at the centre of an active community of physicists, with whom he had extensive interactions and correspondence. In particular, Dirac was in close contact with Bohr, Heisenberg and Pauli. For this reason, among others, Dirac is generally considered a supporter of the Copenhagen interpretation of quantum mechanics. Similarly, he was considered a physicist sympathetic with the positivistic attitude which shaped the development of quantum theory in the 1920s. Against this background, the aim of the present essay is twofold: on the one hand, we will argue that, analyzing specific examples taken from Dirac's published works, he can neither be considered a positivist nor a physicist methodologically guided by the observability doctrine. On the other hand, we will try to disentangle Dirac's figure from the mentioned Copenhagen interpretation, since in his long career he employed remarkably different—and often contradicting—methodological principles and philosophical perspectives with respect to those followed by the supporters of that interpretation.Quanta 2019; 8: 68–87.
Quanta
Swiss National Science Foundation
2019-11-10
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/93
10.12743/quanta.v8i1.93
Quanta; Vol 8, No 1 (2019); 68-87
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/93/120
Copyright (c) 2019 Quanta
oai:ojs.quanta.ws:article/189
2024-02-05T10:33:21Z
quanta:ART
"Mysteries" of Modern Physics and the Fundamental Constants c, h, and G
Stuckey, W. Mark
McDevitt, Timothy
Silberstein, Michael
We review how the kinematic structures of special relativity and quantum mechanics both stem from the relativity principle, i.e., "no preferred reference frame" (NPRF). Essentially, NPRF applied to the measurement of the speed of light c gives the light postulate and leads to the geometry of Minkowski space, while NPRF applied to the measurement of Planck's constant h gives "average-only" projection and leads to the denumerable-dimensional Hilbert space of quantum mechanics. These kinematic structures contain the counterintuitive aspects ("mysteries") of time dilation, length contraction, and quantum entanglement. In this essay, we extend the application of NPRF to the gravitational constant G and show that it leads to the "mystery" of the contextuality of mass in general relativity. Thus, we see an underlying coherence and integrity in modern physics via its "mysteries" and the fundamental constants c, h, and G. It is well known that Minkowski and Einstein were greatly influenced by David Hilbert in their development of special relativity and general relativity, respectively, but relating those theories to quantum mechanics via its non-Boolean Hilbert space kinematics is perhaps surprising.Quanta 2022; 11: 5–14.
Quanta
2022-06-15
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/189
10.12743/quanta.v11i1.189
Quanta; Vol 11, No 1 (2022); 5-14
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/189/146
Copyright (c) 2022 Quanta
oai:ojs.quanta.ws:article/250
2024-02-05T10:33:31Z
quanta:ART
The Enigmas of Fluctuations of the Universal Quantum Fields
Bhaumik, Mani L.
The primary ingredients of reality are the universal quantum fields, which fluctuate persistently, spontaneously, and randomly. The general perception of the scientific community is that these quantum fluctuations are due to the uncertainty principle. Here, we present cogent arguments to show that the uncertainty principle is a consequence of the quantum fluctuations, but not their cause. This poses a conspicuous enigma as to how the universal fields remain immutable with an expectation value so accurate that it leads to experimental results, which are precise to one part in a trillion. We discuss some reasonable possibilities in the absence of a satisfactory solution to this enigma.Quanta 2023; 12: 190–201.
Quanta
2023-12-10
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/250
10.12743/quanta.v12i1.250
Quanta; Vol 12, No 1 (2023); 190-201
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/250/172
Copyright (c) 2023 Quanta
oai:ojs.quanta.ws:article/24
2024-02-05T10:31:41Z
quanta:ART
Realism and Antirealism in Informational Foundations of Quantum Theory
Bilban, Tina
Zeilinger-Brukner's informational foundations of quantum theory, a theory based on Zeilinger's foundational principle for quantum mechanics that an elementary system carried one bit of information, explains seemingly unintuitive quantum behavior with simple theoretical framework. It is based on the notion that distinction between reality and information cannot be made, therefore they are the same. As the critics of informational foundations of quantum theory show, this antirealistic move captures the theory in tautology, where information only refers to itself, while the relationships outside the information with the help of which the nature of information would be defined are lost and the questions "Whose information? Information about what?" cannot be answered. The critic's solution is a return to realism, where the observer's effects on the information are neglected. We show that radical antirealism of informational foundations of quantum theory is not necessary and that the return to realism is not the only way forward. A comprehensive approach that exceeds mere realism and antirealism is also possible: we can consider both sources of the constraints on the information, those coming from the observer and those coming from the observed system/nature/reality. The information is always the observer's information about the observed. Such a comprehensive philosophical approach can still support the theoretical framework of informational foundations of quantum theory: If we take that one bit is the smallest amount of information in the form of which the observed reality can be grasped by the observer, we can say that an elementary system (grasped and defined as such by the observer) correlates to one bit of information. Our approach thus explains all the features of the quantum behavior explained by informational foundations of quantum theory: the wave function and its collapse, entanglement, complementarity and quantum randomness. However, it does so in a more comprehensive and intuitive way. The presented approach is close to Husserl's explanation of the relationship between reality and the knowledge we have about it, and to Bohr's personal explanation of quantum mechanics, the complexity of which has often been missed and simplified to mere antirealism. Our approach thus reconnects phenomenology with contemporary philosophy of science and introduces the comprehensive approach that exceeds mere realism and antirealism to the field of quantum theories with informational foundations, where such an approach has not been taken before.Quanta 2014; 3: 32–42.
Quanta
John Templeton Foundation
2014-08-23
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/24
10.12743/quanta.v3i1.24
Quanta; Vol 3, No 1 (2014); 32-42
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eng
http://quanta.ws/ojs/index.php/quanta/article/view/24/88
oai:ojs.quanta.ws:article/54
2024-02-05T10:32:07Z
quanta:ART
Deciphering the Enigma of Wave-Particle Duality
Bhaumik, Mani L.
A satisfactory explanation of the confounding wave-particle duality of matter is presented in terms of the reality of the wave nature of a particle. In this view, a quantum particle is an objectively real wave packet consisting of irregular disturbances of underlying quantum fields. It travels holistically as a unit and thereby acts as a particle. Only the totality of the entire wave packet at any instance embodies all the conserved quantities, for example the energy-momentum, rest mass, and charge of the particle, and as such must be acquired all at once during detection. On this basis, many of the bizarre behaviors observed in the quantum domain, such as wave function collapse, the limitation of prediction to only a probability rather than an actuality, the apparent simultaneous existence of a particle in more than one place, and the inherent uncertainty can be reasonably comprehended. The necessity of acquiring the wave function in its entirety for detection, as evinced by the appearance of collapse of the wave function, supports the paradigm of reality of the wave function described here.Quanta 2016; 5: 93–100.
Quanta
2016-12-06
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/54
10.12743/quanta.v5i1.54
Quanta; Vol 5, No 1 (2016); 93-100
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/54/83
Copyright (c) 2016 Quanta
oai:ojs.quanta.ws:article/84
2024-02-05T10:32:46Z
quanta:ART
Quantum Trajectories: Dirac, Moyal and Bohm
Hiley, Basil J.
de Gosson, Maurice A.
Dennis, Glen
We recall Dirac's early proposals to develop a description of quantum phenomena in terms of a non-commutative algebra in which he suggested a way to construct what he called quantum trajectories. Generalising these ideas, we show how they are related to weak values and explore their use in the experimental construction of quantum trajectories. We discuss covering spaces which play an essential role in accounting for the wave properties of quantum particles. We briefly point out how new mathematical techniques take us beyond Hilbert space and into a deeper structure which connects with the algebras originally introduced by Born, Heisenberg and Jordan. This enables us to bring out the geometric aspects of quantum phenomena.Quanta 2019; 8: 11–23.
Quanta
Austrian Science Fund (FWF)
Fetzer Franklin Fund
2019-06-05
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/84
10.12743/quanta.v8i1.84
Quanta; Vol 8, No 1 (2019); 11-23
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/84/115
Copyright (c) 2019 Quanta
oai:ojs.quanta.ws:article/157
2024-02-05T10:33:10Z
quanta:ART
Evolution of Open Quantum Systems: Time Scales, Stochastic and Continuous Processes
Khalil, Tarek
Richert, Jean
The study of the physical properties of open quantum systems is at the heart of many investigations, which aim to describe their dynamical evolution on theoretical ground and through physical realizations. Here, we develop a presentation of different aspects, which characterize these systems and confront different physical situations that can be realized leading to systems, which experience Markovian, non-Markovian, divisible or non-divisible interactions with the environments to which they are dynamically coupled. We aim to show how different approaches describe the evolution of quantum systems subject to different types of interactions with their environments.Quanta 2021; 10: 42–54.
Quanta
2021-11-21
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/157
10.12743/quanta.v10i1.157
Quanta; Vol 10, No 1 (2021); 42-54
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/157/134
Copyright (c) 2021 Quanta
oai:ojs.quanta.ws:article/235
2024-02-05T10:33:31Z
quanta:ART
Shor's Factoring Algorithm and Modular Exponentiation Operators
Singleton Jr, Robert L.
We provide a pedagogical presentation of Shor's factoring algorithm, which is a quantum algorithm for factoring very large numbers (of order of hundreds to thousands of bits) in polynomial time. In contrast, all known classical algorithms for the factoring problem take an exponential time to factor such large numbers. Shor's algorithm therefore has profound implication for public-key encryption such as RSA and Diffie–Hellman key exchange. We assume no prior knowledge of Shor's algorithm beyond a basic familiarity with the circuit model of quantum computing. Shor's algorithm contains a number of moving parts, and can be rather daunting at first. The literature is replete with derivations and expositions of Shor's algorithm, but most of them seem to be lacking in essential details, and none of them provide a pedagogical presentation. They require a thicket of appendices and assume a knowledge of quantum algorithms and classical mathematics with which the reader might not be familiar. We therefore start with first principle derivations of the quantum Fourier transform (QFT) and quantum phase estimation (QPE), which are the essential building blocks of Shor's algorithm. We then go on to develop the theory of modular exponentiation (ME) operators, one of the fundamental components of Shor's algorithm, and the place where most of the quantum resources are deployed. We also delve into the number theory that establishes the link between factorization and the period of the modular exponential function. We then apply the QPE algorithm to obtain Shor's factoring algorithm. We also discuss the post-quantum processing and the method of continued fractions, which is used to extract the exact period of the modular exponential function from the approximately measured phase angles of the ME operator. The manuscript then moves on to a series of examples. We first verify the formalism by factoring N=15, the smallest number accessible to Shor's algorithm. We then proceed to factor larger integers, developing a systematic procedure that will find the ME operators for any semi-prime N=p×q (where q and p are prime). Finally, we factor the composite numbers N=21, 33, 35, 143, 247 using the Qiskit simulator. It is observed that the ME operators are somewhat forgiving, and truncated approximate forms are able to extract factors just as well as the exact operators. This is because the method of continued fractions only requires an approximate phase value for its input, which suggests that implementing Shor's algorithm might not be as difficult as first suspected.Quanta 2023; 12: 41–130.
Quanta
2023-09-15
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/235
10.12743/quanta.v12i1.235
Quanta; Vol 12, No 1 (2023); 41-130
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/235/163
http://quanta.ws/ojs/index.php/quanta/article/downloadSuppFile/235/62
Copyright (c) 2023 Quanta
oai:ojs.quanta.ws:article/12
2024-02-05T10:31:25Z
quanta:ART
Pedagogical Review of Quantum Measurement Theory with an Emphasis on Weak Measurements
Svensson, Bengt E. Y.
The quantum theory of measurement has been with us since quantum mechanics was invented. It has recently been invigorated, partly due to the increasing interest in quantum information science. In this partly pedagogical review I attempt to give a self-contained overview of non-relativistic quantum theory of measurement expressed in density matrix formalism. I will not dwell on the applications in quantum information theory; it is well covered by several books in that field. The focus is instead on applications to the theory of weak measurement, as developed by Aharonov and collaborators. Their development of weak measurement combined with what they call post-selection - judiciously choosing not only the initial state of a system (pre-selection) but also its final state - has received much attention recently. Not the least has it opened up new, fruitful experimental vistas, like novel approaches to amplification. But the approach has also attached to it some air of mystery. I will attempt to demystify it by showing that (almost) all results can be derived in a straight-forward way from conventional quantum mechanics. Among other things, I develop the formalism not only to first order but also to second order in the weak interaction responsible for the measurement. I apply it to the so called Leggett-Garg inequalities, also known as Bell inequalities in time. I also give an outline, even if rough, of some of the ingenious experiments that the work by Aharonov and collaborators has inspired. As an application of weak measurement, not related to the approach by Aharonov and collaborators, the formalism also allows me to derive the master equation for the density matrix of an open system in interaction with an environment. An issue that remains in the weak measurement plus post-selection approach is the interpretation of the so called weak value of an observable. Is it a bona fide property of the system considered? I have no definite answer to this question; I shall only exhibit the consequences of the proposed interpretation.Quanta 2013; 2: 18–49.
Quanta
2013-05-15
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/12
10.12743/quanta.v2i1.12
Quanta; Vol 2, No 1 (2013); 18-49
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/12/69
oai:ojs.quanta.ws:article/40
2024-02-05T10:32:07Z
quanta:ART
On the Wavefunction Collapse
Stoica, Ovidiu Cristinel
Wavefunction collapse is usually seen as a discontinuous violation of the unitary evolution of a quantum system, caused by the observation. Moreover, the collapse appears to be nonlocal in a sense which seems at odds with general relativity. In this article the possibility that the wavefunction evolves continuously and hopefully unitarily during the measurement process is analyzed. It is argued that such a solution has to be formulated using a time symmetric replacement of the initial value problem in quantum mechanics. Major difficulties in apparent conflict with unitary evolution are identified, but eventually its possibility is not completely ruled out. This interpretation is in a weakened sense both local and realistic, without contradicting Bell's theorem. Moreover, if it is true, it makes general relativity consistent with quantum mechanics in the semiclassical framework.Quanta 2016; 5: 19–33.
Quanta
2016-01-10
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/40
10.12743/quanta.v5i1.40
Quanta; Vol 5, No 1 (2016); 19-33
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/40/78
Copyright (c) 2016 Quanta
oai:ojs.quanta.ws:article/77
2024-02-05T10:32:35Z
quanta:ART
An Invitation to Quantum Channels
Jagadish, Vinayak
Petruccione, Francesco
Open quantum systems have become an active area of research, owing to its potential applications in many different fields ranging from computation to biology. Here, we review the formalism of dynamical maps used to represent the time evolution of open quantum systems and discuss the various representations and properties of the same, with many examples.Quanta 2018; 7: 54–67.
Quanta
South African Research Chair Initiative (SARChI) of the Department of Science and Technology (DST) and the National Research Foundation (NRF)
2018-07-26
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/77
10.12743/quanta.v7i1.77
Quanta; Vol 7, No 1 (2018); 54-67
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/77/109
Copyright (c) 2018 Quanta
oai:ojs.quanta.ws:article/142
2024-02-05T10:32:57Z
quanta:ART
Is the Quantum State Real in the Hilbert Space Formulation?
Bhaumik, Mani L.
The persistent debate about the reality of a quantum state has recently come under limelight because of its importance to quantum information and the quantum computing community. Almost all of the deliberations are taking place using the elegant and powerful but abstract Hilbert space formalism of quantum mechanics developed with seminal contributions from John von Neumann. Since it is rather difficult to get a direct perception of the events in an abstract vector space, it is hard to trace the progress of a phenomenon. Among the multitude of recent attempts to show the reality of the quantum state in Hilbert space, the Pusey–Barrett–Rudolph theory gets most recognition for their proof. But some of its assumptions have been criticized, which are still not considered to be entirely loophole free. A straightforward proof of the reality of the wave packet function of a single particle has been presented earlier based on the currently recognized fundamental reality of the universal quantum fields. Quantum states like the atomic energy levels comprising the wave packets have been shown to be just as real. Here we show that an unambiguous proof of reality of the quantum states gleaned from the reality of quantum fields can also provide an explicit substantiation of the reality of quantum states in Hilbert space.Quanta 2020; 9: 37–46.
Quanta
2020-12-19
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/142
10.12743/quanta.v9i1.142
Quanta; Vol 9, No 1 (2020); 37-46
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/142/127
Copyright (c) 2020 Quanta
oai:ojs.quanta.ws:article/199
2024-02-05T10:33:21Z
quanta:ART
Clifford Algebras, Spin Groups and Qubit Trees
Vlasov, Alexander Yurievich
Representations of Spin groups and Clifford algebras derived from the structure of qubit trees are introduced in this work. For ternary trees the construction is more general and reduction to binary trees is formally defined by deletion of superfluous branches. The usual Jordan–Wigner construction also may be formally obtained in this approach by bringing the process up to trivial qubit chain (trunk). The methods can also be used for effective simulation of some quantum circuits corresponding to the binary tree structure. The modeling of more general qubit trees, as well as the relationship with the mapping used in the Bravyi–Kitaev transformation, are also briefly discussed.Quanta 2022; 11: 97–114.
Quanta
2022-12-01
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/199
10.12743/quanta.v11i1.199
Quanta; Vol 11, No 1 (2022); 97-114
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/199/153
Copyright (c) 2022 Quanta
oai:ojs.quanta.ws:article/4
2024-02-05T10:30:58Z
quanta:ART
A Historical Survey of Sir Karl Popper's Contribution to Quantum Mechanics
Shields, William M.
Sir Karl Popper (1902-1994), though not trained as a physicist and embarrassed early in his career by a physics error pointed out by Einstein and Bohr, ultimately made substantial contributions to the interpretation of quantum mechanics. As was often the case, Popper initially formulated his position by criticizing the views of others - in this case Niels Bohr and Werner Heisenberg. Underlying Popper's criticism was his belief that, first, the Copenhagen interpretation of quantum mechanics abandoned scientific realism and second, the assertion that quantum theory was complete (an assertion rejected by Einstein among others) amounted to an unfalsifiable claim. Popper insisted that the most basic predictions of quantum mechanics should continue to be tested, with an eye towards falsification rather than mere adding of decimal places to confirmatory experiments. His persistent attacks on the Copenhagen interpretation were aimed not at the uncertainty principle itself and the formalism from which it was derived, but at the acceptance by physicists of an unclear epistemology and ontology that left critical questions unanswered.Quanta 2012; 1: 1–12.
Quanta
2012-11-15
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/1
10.12743/quanta.v1i1.4
Quanta; Vol 1, No 1 (2012); 1-12
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eng
http://quanta.ws/ojs/index.php/quanta/article/view/1/62
oai:ojs.quanta.ws:article/31
2024-02-05T10:31:55Z
quanta:ART
Timeless Approach to Quantum Jumps
Licata, Ignazio
Chiatti, Leonardo
According to the usual quantum description, the time evolution of the quantum state is continuous and deterministic except when a discontinuous and indeterministic collapse of state vector occurs. The collapse has been a central topic since the origin of the theory, although there are remarkable theoretical proposals to understand its nature, such as the Ghirardi–Rimini–Weber. Another possibility could be the assimilation of collapse with the now experimentally well established phenomenon of quantum jump, postulated by Bohr already in 1913. The challenge of nonlocality offers an opportunity to reconsider the quantum jump as a fundamental element of the logic of the physical world, rather than a subsidiary accident. We propose here a simple preliminary model that considers quantum jumps as processes of entry to and exit from the usual temporal domain to a timeless vacuum, without contradicting the quantum relativistic formalism, and we present some potential connections with particle physics.Quanta 2015; 4: 10–26.
Quanta
2015-10-11
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/31
10.12743/quanta.v4i1.31
Quanta; Vol 4, No 1 (2015); 10-26
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/31/85
Copyright (c) 2015 Quanta
oai:ojs.quanta.ws:article/68
2024-02-05T10:32:20Z
quanta:ART
Is Schrödinger's Cat Alive?
Bhaumik, Mani L.
Erwin Schrödinger is famous for presenting his wave equation of motion that jump-started quantum mechanics. His disenchantment with the Copenhagen interpretation of quantum mechanics led him to unveil the Schrödinger's cat paradox, which did not get much attention for nearly half a century. In the meantime, disappointment with quantum mechanics turned his interest to biology facilitating, albeit in a peripheral way, the revelation of the structure of DNA. Interest in Schrödinger's cat has recently come roaring back making its appearance conspicuously in numerous scientific articles. From the arguments presented here, it would appear that the legendary Schrödinger's cat is here to stay, symbolizing a profound truth that quantum reality exists at all scales; but we do not observe it in our daily macroscopic world as it is masked for all practical purposes, most likely by environmental decoherence with irreversible thermal effects.Quanta 2017; 6: 70–80.
Quanta
2017-12-11
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/68
10.12743/quanta.v6i1.68
Quanta; Vol 6, No 1 (2017); 70-80
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/68/99
Copyright (c) 2017 Quanta
oai:ojs.quanta.ws:article/96
2024-02-05T10:32:46Z
quanta:ART
How Dirac's Seminal Contributions Pave the Way for Comprehending Nature's Deeper Designs
Bhaumik, Mani L.
Credible reasons are presented to reveal that many of the lingering century old enigmas, surrounding the behavior of at least an individual quantum particle, can be comprehended in terms of an objectively real specific wave function. This wave function is gleaned from the single particle energy-momentum eigenstate offered by the theory of space filling universal quantum fields that is an inevitable outcome of Dirac's pioneering masterpiece. Examples of these well-known enigmas are wave particle duality, the de Broglie hypothesis, the uncertainty principle, wave function collapse, and predictions of measurement outcomes in terms of probability instead of certainty. Paul Dirac successfully incorporated special theory of relativity into quantum mechanics for the first time. This was accomplished through his ingenious use of matrices that allowed the equations of motion to maintain the necessary first order time derivative feature necessary for positive probability density. The ensuing Dirac equation for the electron led to the recognition of the mystifying quantized spin and magnetic moment as intrinsic properties in contrast to earlier ad hoc assumptions. The solution of his relativistic equation for the hydrogen atom produced results in perfect agreement with experimental data available at the time. The most far reaching prediction of the celebrated Dirac equation was the totally unexpected existence of anti-particles, culminating in the eventual development of the quantum field theory of the Standard Model that reveals the deepest secrets of the universe known to date.Quanta 2019; 8: 88–100.
Quanta
2019-12-17
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/96
10.12743/quanta.v8i1.96
Quanta; Vol 8, No 1 (2019); 88-100
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/96/121
Copyright (c) 2019 Quanta
oai:ojs.quanta.ws:article/197
2024-02-05T10:33:21Z
quanta:ART
Dual Instruments and Sequential Products of Observables
Gudder, Stan
We first show that every operation possesses an unique dual operation and measures an unique effect. If a and b are effects and J is an operation that measures a, we define the sequential product of a then b relative to J. Properties of the sequential product are derived and are illustrated in terms of Lüders and Holevo operations. We next extend this work to the theory of instruments and observables. We also define the concept of an instrument (observable) conditioned by another instrument (observable). Identity, state-constant and repeatable instruments are considered. Sequential products of finite observables relative to Lüders and Holevo instruments are studied.Quanta 2022; 11: 15–27.
Quanta
2022-08-30
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/197
10.12743/quanta.v11i1.197
Quanta; Vol 11, No 1 (2022); 15-27
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/197/148
Copyright (c) 2022 Quanta
oai:ojs.quanta.ws:article/259
2024-02-06T10:07:07Z
quanta:ART
Conditional Effects, Observables and Instruments
Gudder, Stan
We begin with a study of operations and the effects they measure. We define the probability that an effect $a$ occurs when the system is in a state $\rho$ by $P_{\rho}(a)=\textrm{Tr}(\rho a)$. If $P_{\rho}(a)\ne0$ and $\mathcal{I}$ is an operation that measures $a$, we define the conditional probability of an effect $b$ given $a$ relative to $\mathcal{I}$ by $P_{\rho}(b\mid a)=\textrm{Tr}[\mathcal{I}(\rho)b]/P_{\rho}(a)$. We characterize when Bayes' quantum second rule $P_{\rho}(b\mid a)=\frac{P_{\rho}(b)}{P_{\rho}(a)}\,P_{\rho}(a\mid b)$ holds. We then consider Lüders and Holevo operations. We next discuss instruments and the observables they measure. If $A$ and $B$ are observables and an instrument $\mathcal{I}$ measures $A$, we define the observable $B$ conditioned on $A$ relative to $\mathcal{I}$ and denote it by $(B\mid A)$. Using these concepts, we introduce Bayes' quantum first rule. We observe that this is the same as the classical Bayes' first rule, except it depends on the instrument used to measure $A$. We then extend this to Bayes' quantum first rule for expectations. We show that two observables $B$ and $C$ are jointly commuting if and only if there exists an atomic observable $A$ such that $B=(B\mid A)$ and $C=(C\mid A)$. We next obtain a general uncertainty principle for conditioned observables. Finally, we discuss observable conditioned quantum entropies. The theory is illustrated with many examples.Quanta 2024; 13: 1–10.
Quanta
2024-02-06
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/259
10.12743/quanta.v13i1.259
Quanta; Vol 13, No 1 (2024); 1-10
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/259/173
Copyright (c) 2024 Quanta
oai:ojs.quanta.ws:article/25
2024-02-05T10:31:41Z
quanta:ART
Is Bohm's Interpretation Consistent with Quantum Mechanics?
Nauenberg, Michael
The supposed equivalence of the conventional interpretation of quantum mechanics with Bohm's interpretation is generally demonstrated only in the coordinate representation. It is shown, however, that in the momentum representation this equivalence is not valid.Quanta 2014; 3: 43–46.
Quanta
2014-08-23
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/25
10.12743/quanta.v3i1.25
Quanta; Vol 3, No 1 (2014); 43-46
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/25/89
oai:ojs.quanta.ws:article/57
2024-02-05T10:32:20Z
quanta:ART
Quantum Cryptography: Key Distribution and Beyond
Shenoy-Hejamadi, Akshata
Pathak, Anirban
Radhakrishna, Srikanth
Uniquely among the sciences, quantum cryptography has driven both foundational research as well as practical real-life applications. We review the progress of quantum cryptography in the last decade, covering quantum key distribution and other applications.Quanta 2017; 6: 1–47.
Quanta
Swiss Government Excellence Postdoctoral Fellowship
Defense Research and Development Organization (DRDO), India project ERIP/ER/1403163/M/01/1603
2017-06-18
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/57
10.12743/quanta.v6i1.57
Quanta; Vol 6, No 1 (2017); 1-47
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/57/100
Copyright (c) 2017 Quanta
oai:ojs.quanta.ws:article/87
2024-02-05T10:32:46Z
quanta:ART
Coherence, Interference and Visibility
Qureshi, Tabish
The interference observed for a quanton, traversing more than one path, is believed to characterize its wave nature. Conventionally, the sharpness of interference has been quantified by its visibility or contrast, as defined in optics. Based on this visibility, wave-particle duality relations have been formulated for two-path interference. However, as one generalizes the situation to multi-path interference, it is found that conventional interference visibility is not a good quantifier. A recently introduced measure of quantum coherence has been shown to be a good quantifier of the wave nature. The subject of quantum coherence, in relation to the wave nature of quantons and to interference visibility, is reviewed here. It is argued that coherence can be construed as a more general form of interference visibility, if the visibility is measured in a different manner, and not as contrast.Quanta 2019; 8: 24–35.
Quanta
2019-06-17
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/87
10.12743/quanta.v8i1.87
Quanta; Vol 8, No 1 (2019); 24-35
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/87/116
Copyright (c) 2019 Quanta
oai:ojs.quanta.ws:article/162
2024-02-05T10:33:10Z
quanta:ART
Revisiting the Quantum Open System Dynamics of Central Spin Model
Bhattacharya, Samyadeb
Banerjee, Subhashish
In this work, we revisit the theory of open quantum systems from the perspective of fermionic baths. Specifically, we concentrate on the dynamics of a central spin half particle interacting with a spin bath. We have calculated the exact reduced dynamics of the central spin and constructed the Kraus operators in relation to that. Further, the exact Lindblad type canonical master equation corresponding to the reduced dynamics is constructed. We have also briefly touched upon the aspect of non-Markovianity from the backdrop of the reduced dynamics of the central spin.Quanta 2021; 10: 55–64.
Quanta
2021-12-12
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/162
10.12743/quanta.v10i1.162
Quanta; Vol 10, No 1 (2021); 55-64
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/162/135
Copyright (c) 2021 Quanta
oai:ojs.quanta.ws:article/226
2024-02-05T10:33:31Z
quanta:ART
Digital Simulation of Single Qubit Markovian Open Quantum Systems: A Tutorial
David, Ian Joel
Sinayskiy, Ilya
Petruccione, Francesco
One of the first proposals for the use of quantum computers was the simulation of quantum systems. Over the past three decades, great strides have been made in the development of algorithms for simulating closed quantum systems and the more complex open quantum systems. In this tutorial, we introduce the methods used in the simulation of single qubit Markovian open quantum systems. It combines various existing notations into a common framework that can be extended to more complex open system simulation problems. The only currently available algorithm for the digital simulation of single qubit open quantum systems is discussed in detail. A modification to the implementation of the simpler channels is made that removes the need for classical random sampling, thus making the modified algorithm a strictly quantum algorithm. The modified algorithm makes use of quantum forking to implement the simpler channels that approximate the total channel. This circumvents the need for quantum circuits with a large number of CNOT gates.Quanta 2023; 12: 131–163.
Quanta
National Research Foundation of the Republic of South Africa
National Integrated Cyber Infrastructure System (NICIS) e-research grant QICSA
2023-09-18
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/226
10.12743/quanta.v12i1.226
Quanta; Vol 12, No 1 (2023); 131-163
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/226/162
Copyright (c) 2023 Quanta
oai:ojs.quanta.ws:article/11
2024-02-05T10:31:25Z
quanta:ART
Einstein's Recoiling Slit Experiment, Complementarity and Uncertainty
Qureshi, Tabish
Vathsan, Radhika
We analyze Einstein's recoiling slit experiment and point out that the inevitable entanglement between the particle and the recoiling slit was not part of Bohr's reply. We show that if this entanglement is taken into account, one can provide a simpler answer to Einstein. We also derive the Englert-Greenberger-Yasin duality relation from the entanglement between the particle and the recoiling slit. In addition, we show that the Englert-Greenberger-Yasin duality relation can also be thought of as a consequence of the sum uncertainty relation for certain observables of the recoiling slit. Thus, the uncertainty relations and entanglement are both an integral part of the which-way detection process.Quanta 2013; 2: 58–65.
Quanta
2013-05-15
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/11
10.12743/quanta.v2i1.11
Quanta; Vol 2, No 1 (2013); 58-65
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/11/71
oai:ojs.quanta.ws:article/41
2024-02-05T10:32:07Z
quanta:ART
Towards a Realistic Parsing of the Feynman Path Integral
Wharton, Ken
The Feynman path integral does not allow a one real path interpretation, because the quantum amplitudes contribute to probabilities in a non-separable manner. The opposite extreme, all paths happen, is not a useful or informative account. In this paper it is shown that an intermediate parsing of the path integral, into realistic non-interfering possibilities, is always available. Each realistic possibility formally corresponds to numerous particle paths, but is arguably best interpreted as a spacetime-valued field. Notably, one actual field history can always be said to occur, although it will generally not have an extremized action. The most obvious concerns with this approach are addressed, indicating necessary follow-up research. But without obvious showstoppers, it seems plausible that the path integral might be reinterpreted to explain quantum phenomena in terms of Lorentz covariant field histories.Quanta 2016; 5: 1–11.
Quanta
2016-01-10
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/41
10.12743/quanta.v5i1.41
Quanta; Vol 5, No 1 (2016); 1-11
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/41/76
Copyright (c) 2016 Quanta
oai:ojs.quanta.ws:article/79
2024-02-05T10:32:35Z
quanta:ART
John Bell and the Great Enterprise
Sudbery, Anthony
I outline Bell's vision of the "great enterprise" of science, and his view that conventional teachings about quantum mechanics constituted a betrayal of this enterprise. I describe a proposal of his to put the theory on a more satisfactory footing, and review the subsequent uses that have been made of one element of this proposal, namely Bell's transition probabilities regarded as fundamental physical processes.Quanta 2018; 7: 68–73.
Quanta
2018-09-02
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/79
10.12743/quanta.v7i1.79
Quanta; Vol 7, No 1 (2018); 68-73
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/79/110
Copyright (c) 2018 Quanta
oai:ojs.quanta.ws:article/148
2024-02-05T10:33:10Z
quanta:ART
On the Connection Between Quantum Probability and Geometry
Holik, Federico Hernán
We discuss the mathematical structures that underlie quantum probabilities. More specifically, we explore possible connections between logic, geometry and probability theory. We propose an interpretation that generalizes the method developed by R. T. Cox to the quantum logical approach to physical theories. We stress the relevance of developing a geometrical interpretation of quantum mechanics.Quanta 2021; 10: 1–14.
Quanta
2021-06-18
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/148
10.12743/quanta.v10i1.148
Quanta; Vol 10, No 1 (2021); 1-14
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/148/129
Copyright (c) 2021 Quanta
oai:ojs.quanta.ws:article/208
2024-02-05T10:33:21Z
quanta:ART
Can Decoherence Solve the Measurement Problem?
Bhaumik, Mani L.
The quantum decoherence program has become more attractive in providing an acceptable solution for the long-standing quantum measurement problem. Decoherence by quantum entanglement happens very quickly to entangle the quantum system with the environment including the detector. But in the final stage of measurement, acquiring the unentangled pointer states poses some problems. Recent experimental observations of the effect of the ubiquitous quantum vacuum fluctuations in destroying quantum entanglement appears to provide a solution.Quanta 2022; 11: 115–123.
Quanta
2022-12-04
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/208
10.12743/quanta.v11i1.208
Quanta; Vol 11, No 1 (2022); 115-123
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/208/154
Copyright (c) 2022 Quanta
oai:ojs.quanta.ws:article/9
2024-02-05T10:30:58Z
quanta:ART
Popper and Bohr on Realism in Quantum Mechanics
Howard, Don
Popper's program in the foundations of quantum mechanics defending objectivity and realism developed out of a profound dissatisfaction with the point of view associated with Bohr, which is usually designated the Copenhagen interpretation. Here I will argue that while Popper's aim is a noble one, his program does not succeed on two counts: he does not succeed in showing that Bohr's philosophy must be rejected as a variety of subjectivism, and his alternative interpretation of indeterminacy rests on a highly questionable assumption according to which simultaneously precise conjugate parameters are possible. Nevertheless I like Popper's propensity interpretation of probability and think that the propensity idea deserves further research.Quanta 2012; 1: 33–57.
Quanta
2012-11-15
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/4
10.12743/quanta.v1i1.9
Quanta; Vol 1, No 1 (2012); 33-57
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/4/65
oai:ojs.quanta.ws:article/46
2024-02-05T10:31:55Z
quanta:ART
The Phase Space Formulation of Time-Symmetric Quantum Mechanics
de Gosson, Charlyne
de Gosson, Maurice A.
Time-symmetric quantum mechanics can be described in the Weyl–Wigner–Moyal phase space formalism by using the properties of the cross-terms appearing in the Wigner distribution of a sum of states. These properties show the appearance of a strongly oscillating interference between the pre-selected and post-selected states. It is interesting to note that the knowledge of this interference term is sufficient to reconstruct both states.Quanta 2015; 4: 27–34.
Quanta
FWF Austrian Science Fund
2015-11-23
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/46
10.12743/quanta.v4i1.46
Quanta; Vol 4, No 1 (2015); 27-34
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/46/86
Copyright (c) 2015 Quanta
oai:ojs.quanta.ws:article/67
2024-02-05T10:32:35Z
quanta:ART
Biphoton Interference in a Double-Slit Experiment
Paul, Ananya
Qureshi, Tabish
A double-slit experiment with entangled photons is theoretically analyzed. It is shown that, under suitable conditions, two entangled photons of wavelength λ can behave like a biphoton of wavelength λ/2. The interference of these biphotons, passing through a double-slit can be obtained by detecting both photons of the pair at the same position. This is in agreement with the results of an earlier experiment. More interestingly, we show that even if the two entangled photons are separated by a polarizing beam splitter, they can still behave like a biphoton of wavelength λ/2. In this modified setup, the two separated photons passing through two different double-slits, surprisingly show an interference corresponding to a wavelength λ/2, instead of λ which is the wavelength of each photon. We point out two experiments that have been carried out in different contexts, which saw the effect predicted here without realizing this connection.Quanta 2018; 7: 1–6.
Quanta
2018-02-19
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/67
10.12743/quanta.v7i1.67
Quanta; Vol 7, No 1 (2018); 1-6
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/67/102
Copyright (c) 2018 Quanta
oai:ojs.quanta.ws:article/113
2024-02-05T10:32:57Z
quanta:ART
Quantum Entanglement: Spooky Action at a Distance
Gudder, Stan
Quantum entanglement is an important resource in quantum information technologies. Here, we study and characterize in a precise mathematical language some of the weird and nonintuitive features of quantum entanglement. We begin by illustrating why entanglement implies action at a distance. We then introduce a simple criterion for determining when a pure quantum state is entangled. Finally, we present a measure for the amount of entanglement for a pure state.Quanta 2020; 9: 1–6.
Quanta
2020-06-16
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/113
10.12743/quanta.v9i1.113
Quanta; Vol 9, No 1 (2020); 1-6
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/113/124
Copyright (c) 2020 Quanta
oai:ojs.quanta.ws:article/195
2024-02-05T10:33:21Z
quanta:ART
On the Role of Inconsistency in Quantum Foundational Debate and Hilbert Space Formulation
Gangopadhyay, Debajyoti
This article is intended mainly to develop an expository outline of an inherently inconsistent reasoning in the development of quantum mechanics during 1920s, which set up the background of proposing different variants of quantum logic a bit later. We will discuss here two of the quantum logical variants with reference to Hilbert space formulation, based on the proposals of Bohr and Schrödinger as a result of addressing the same kernel of difficulties and will give a relative comparison. Our presentation is fairly informal, as our goal here is to simply sketch the central ideas leaving further details for other occasions.Quanta 2022; 11: 28–41.
Quanta
2022-10-05
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/195
10.12743/quanta.v11i1.195
Quanta; Vol 11, No 1 (2022); 28-41
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/195/149
Copyright (c) 2022 Quanta
oai:ojs.quanta.ws:article/27
2024-02-05T10:31:41Z
quanta:ART
Ontology and Quantum Mechanics
Hari Dass, N. D.
The issue of ontology in quantum mechanics, or equivalently the issue of the reality of the wave function is critically examined within standard quantum theory. It is argued that though no strict ontology is possible within quantum theory, ingenious measurement schemes may still make the notion of a FAPP ontology (ontology for all practical purposes) meaningful and useful.Quanta 2014; 3: 47–66.
Quanta
2014-09-22
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/27
10.12743/quanta.v3i1.27
Quanta; Vol 3, No 1 (2014); 47-66
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/27/90
oai:ojs.quanta.ws:article/60
2024-02-05T10:32:20Z
quanta:ART
Erwin Schrödinger and Quantum Wave Mechanics
O'Connor, John J.
Robertson, Edmund F.
The fathers of matrix quantum mechanics believed that the quantum particles are unanschaulich (unvisualizable) and that quantum particles pop into existence only when we measure them. Challenging the orthodoxy, in 1926 Erwin Schrödinger developed his wave equation that describes the quantum particles as a packet of quantum probability amplitudes evolving in space and time. Thus, Schrödinger visualized the unvisualizable and lifted the veil that has been obscuring the wonders of the quantum world.Quanta 2017; 6: 48–52.
Quanta
2017-08-22
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/60
10.12743/quanta.v6i1.60
Quanta; Vol 6, No 1 (2017); 48-52
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/60/75
Copyright (c) 2017 Quanta
oai:ojs.quanta.ws:article/90
2024-02-05T10:32:46Z
quanta:ART
Improving the Cauchy–Schwarz Inequality
Bhattacharyya, Kamal
We highlight overlap as one of the simplest inequalities in linear space that yields a number of useful results. One obtains the Cauchy–Schwarz inequality as a special case. More importantly, a variant of it is seen to work desirably in certain singular situations where the celebrated inequality appears to be useless. The basic tenet generates a few other interesting relations, including the improvements over certain common uncertainty bounds. Role of projection operators in modifying the Cauchy–Schwarz relation is noted. Selected applications reveal the efficacy.Quanta 2019; 8: 36-43.
Quanta
2019-08-03
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/90
10.12743/quanta.v8i1.90
Quanta; Vol 8, No 1 (2019); 36-43
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/90/117
Copyright (c) 2019 Quanta
oai:ojs.quanta.ws:article/173
2024-02-05T10:33:10Z
quanta:ART
How Do the Probabilities Arise in Quantum Measurement?
Bhaumik, Mani L.
A satisfactory resolution of the persistent quantum measurement problem remains stubbornly unresolved in spite of an overabundance of efforts of many prominent scientists over the decades. Among others, one key element is considered yet to be resolved. It comprises of where the probabilities of the measurement outcome stem from. This article attempts to provide a plausible answer to this enigma, thus eventually making progress toward a cogent solution of the longstanding measurement problem.Quanta 2021; 10: 65–74.
Quanta
2021-12-17
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/173
10.12743/quanta.v10i1.173
Quanta; Vol 10, No 1 (2021); 65-74
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/173/136
Copyright (c) 2021 Quanta
oai:ojs.quanta.ws:article/241
2024-02-05T10:33:31Z
quanta:ART
Quantum Mechanics with Real Numbers: Entanglement, Superselection Rules and Gauges
Vedral, Vlatko
We show how imaginary numbers in quantum physics can be eliminated by enlarging the Hilbert space followed by an imposition of—what effectively amounts to—a superselection rule. We illustrate this procedure with a qubit and apply it to the Mach–Zehnder interferometer. The procedure is somewhat reminiscent of the constrained quantization of the electromagnetic field, where, in order to manifestly comply with relativity, one enlarges the Hilbert Space by quantizing the longitudinal and scalar modes, only to subsequently introduce a constraint to make sure that they are actually not directly observable.Quanta 2023; 12: 164–170.
Quanta
Moore Foundation
John Templeton Foundation
2023-09-24
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/241
10.12743/quanta.v12i1.241
Quanta; Vol 12, No 1 (2023); 164-170
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/241/164
Copyright (c) 2023 Quanta
oai:ojs.quanta.ws:article/15
2024-02-05T10:31:25Z
quanta:ART
Are the Weak Measurements Really Measurements?
Sokolovski, Dmitri
Weak measurements can be seen as an attempt at answering the Which way? question without destroying interference between the pathways involved. Unusual mean values obtained in such measurements represent the response of a quantum system to this forbidden question, in which the true composition of virtual pathways is hidden from the observer. Such values indicate a failure of a measurement where the uncertainty principle says it must fail, rather than provide an additional insight into physical reality.Quanta 2013; 2: 50–57.
Quanta
2013-05-15
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/15
10.12743/quanta.v2i1.15
Quanta; Vol 2, No 1 (2013); 50-57
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/15/70
oai:ojs.quanta.ws:article/45
2024-02-05T10:32:07Z
quanta:ART
Antimatter in the Direct-Action Theory of Fields
Kastner, Ruth E.
One of Feynman's greatest contributions to physics was the interpretation of negative energies as antimatter in quantum field theory. A key component of this interpretation is the Feynman propagator, which seeks to describe the behavior of antimatter at the virtual particle level. Ironically, it turns out that one can dispense with the Feynman propagator in a direct-action theory of fields, while still retaining the interpretation of negative energy solutions as antiparticles.Quanta 2016; 5: 12–18.
Quanta
2016-01-10
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/45
10.12743/quanta.v5i1.45
Quanta; Vol 5, No 1 (2016); 12-18
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/45/77
Copyright (c) 2016 Quanta
oai:ojs.quanta.ws:article/74
2024-02-05T10:32:35Z
quanta:ART
Quantum Harmonic Analysis of the Density Matrix
de Gosson, Maurice A.
We will study rigorously the notion of mixed states and their density matrices. We will also discuss the quantum-mechanical consequences of possible variations of Planck's constant h. This review has been written having in mind two readerships: mathematical physicists and quantum physicists. The mathematical rigor is maximal, but the language and notation we use throughout should be familiar to physicists.Quanta 2018; 7: 74–110.
Quanta
Austrian Research Foundation FWF (Fonds zur Förderung der wissenschaftlichen Forschung)
2018-09-26
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/74
10.12743/quanta.v7i1.74
Quanta; Vol 7, No 1 (2018); 74-110
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/74/111
Copyright (c) 2018 Quanta
oai:ojs.quanta.ws:article/163
2024-02-05T10:33:10Z
quanta:ART
Entanglement Robustness in Trace Decreasing Quantum Dynamics
Filippov, Sergey N.
Trace decreasing dynamical maps are as physical as trace preserving ones; however, they are much less studied. Here we overview how the quantum Sinkhorn theorem can be successfully applied to find a two-qubit entangled state which has the strongest robustness against local noises and losses of quantum information carriers. We solve a practically relevant problem of finding an optimal initial encoding to distribute entangled polarized qubits through communication lines with polarization dependent losses and extra depolarizing noise. The longest entanglement lifetime is shown to be attainable with a state that is not maximally entangled.Quanta 2021; 10: 15–21.
Quanta
Russian Science Foundation
2021-09-07
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/163
10.12743/quanta.v10i1.163
Quanta; Vol 10, No 1 (2021); 15-21
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/163/130
Copyright (c) 2021 Quanta
oai:ojs.quanta.ws:article/210
2024-02-05T10:33:31Z
quanta:ART
Role of Steering Inequality in Quantum Key Distribution Protocol
Mukherjee, Kaushiki
Patro, Tapaswini
Ganguly, Nirman
Violation of Bell's inequality has been the mainspring for secure key generation in an entanglement assisted Quantum Key Distribution (QKD) protocol. Various contributions have relied on the violation of Bell inequalities to build an appropriate QKD protocol. Residing between Bell nonlocality and entanglement, there exists a hybrid trait of correlations, namely correlations exhibited through the violation of steering inequalities. However, such correlations have not been put to use in QKD protocols as much as their stronger counterpart, the Bell violations. In the present work, we show that the violations of the Cavalcanti–Jones–Wiseman–Reid (CJWR) steering inequalities can act as key ingredients in an entanglement assisted QKD protocol. We work with arbitrary two-qubit entangled states, and characterize them by their utility in such protocols. The characterization is based on the quantum bit error rate and violation of the CJWR inequality. Furthermore, we show that subsequent applications of local filtering operations on initially entangled states exhibiting no violation, lead to violations necessary for the successful implementation of the protocol. An additional vindication of our protocol is provided by the use of absolutely Bell–Clauser–Horne–Shimony–Holt (Bell–CHSH) local states, states which remain Bell–CHSH local even under global unitary operations.Quanta 2023; 12: 1–21.
Quanta
2023-04-18
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/210
10.12743/quanta.v12i1.210
Quanta; Vol 12, No 1 (2023); 1-21
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/210/156
Copyright (c) 2023 Quanta
oai:ojs.quanta.ws:article/5
2024-02-05T10:30:58Z
quanta:ART
Morlet Wavelets in Quantum Mechanics
Ashmead, John
Wavelets offer significant advantages for the analysis of problems in quantum mechanics. Because wavelets are localized in both time and frequency they avoid certain subtle but potentially fatal conceptual errors that can result from the use of plane wave or δ function decomposition. Morlet wavelets in particular are well-suited for this work: as Gaussians, they have a simple analytic form and they work well with Feynman path integrals. But to take full advantage of Morlet wavelets we need to supply an explicit form for the inverse Morlet transform and a manifestly covariant form for the four-dimensional Morlet wavelet. We construct both here.Quanta 2012; 1: 58–70.
Quanta
2012-11-15
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/5
10.12743/quanta.v1i1.5
Quanta; Vol 1, No 1 (2012); 58-70
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eng
http://quanta.ws/ojs/index.php/quanta/article/view/5/66
oai:ojs.quanta.ws:article/47
2024-02-05T10:31:55Z
quanta:ART
Was Albert Einstein Wrong on Quantum Physics?
Bhaumik, Mani L.
Albert Einstein is considered by many physicists as the father of quantum physics in some sense. Yet there is an unshakable view that he was wrong on quantum physics. Although it may be a subject of considerable debate, the core of his allegedly wrong demurral was the insistence on finding an objective reality underlying the manifestly bizarre behavior of quantum objects. The uncanny wave-particle duality of a quantum particle is a prime example. In view of the latest developments, particularly in quantum field theory, the objections of Einstein are substantially corroborated. Careful investigation suggests that a travelling quantum particle is a holistic wave packet consisting of an assemblage of irregular disturbances in quantum fields. It acts as a particle because only the totality of all the disturbances in the wave packet yields the energy-momentum with the mass of a particle, along with its other conserved quantities such as charge and spin. Thus the wave function representing a particle is not just a fictitious mathematical construct but embodies a reality of nature as asserted by Einstein.Quanta 2015; 4: 35–42.
Quanta
2015-12-11
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/47
10.12743/quanta.v4i1.47
Quanta; Vol 4, No 1 (2015); 35-42
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/47/87
Copyright (c) 2015 Quanta
oai:ojs.quanta.ws:article/65
2024-02-05T10:32:35Z
quanta:ART
A Quantum Implementation Model for Artificial Neural Networks
Daskin, Ammar
The learning process for multilayered neural networks with many nodes makes heavy demands on computational resources. In some neural network models, the learning formulas, such as the Widrow–Hoff formula, do not change the eigenvectors of the weight matrix while flatting the eigenvalues. In infinity, these iterative formulas result in terms formed by the principal components of the weight matrix, namely, the eigenvectors corresponding to the non-zero eigenvalues. In quantum computing, the phase estimation algorithm is known to provide speedups over the conventional algorithms for the eigenvalue-related problems. Combining the quantum amplitude amplification with the phase estimation algorithm, a quantum implementation model for artificial neural networks using the Widrow–Hoff learning rule is presented. The complexity of the model is found to be linear in the size of the weight matrix. This provides a quadratic improvement over the classical algorithms.Quanta 2018; 7: 7–18.
Quanta
2018-02-20
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/65
10.12743/quanta.v7i1.65
Quanta; Vol 7, No 1 (2018); 7-18
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/65/104
Copyright (c) 2018 Quanta
oai:ojs.quanta.ws:article/115
2024-02-05T10:32:57Z
quanta:ART
A Theory of Entanglement
Gudder, Stan
This article presents the basis of a theory of entanglement. We begin with a classical theory of entangled discrete measures. Then, we treat quantum mechanics and discuss the statistics of bounded operators on a Hilbert space in terms of context coefficients. Finally, we combine both topics to develop a general theory of entanglement for quantum states. A measure of entanglement called the entanglement number is introduced. Although this number is related to entanglement robustness, its motivation is not the same and there are some differences. The present article only involves bipartite systems and we leave the study of multipartite systems for later work.Quanta 2020; 9: 7–15.
Quanta
2020-07-27
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/115
10.12743/quanta.v9i1.115
Quanta; Vol 9, No 1 (2020); 7-15
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/115/123
Copyright (c) 2020 Quanta
oai:ojs.quanta.ws:article/202
2024-02-05T10:33:21Z
quanta:ART
The Quantum Hamilton–Jacobi Equation and the Link Between Classical and Quantum Mechanics
Fusco Girard, Mario
We study how the classical Hamilton's principal and characteristic functions are generated from the solutions of the quantum Hamilton–Jacobi equation. While in the classically forbidden regions these quantum quantities directly tend to the classical ones, this is not the case in the allowed regions. There, the limit is reached only if the quantum fluctuations are eliminated by means of coarse-graining averages. Analogously, the classical Hamilton–Jacobi scheme bringing to the motion's equations arises from a similar formal quantum procedure.Quanta 2022; 11: 42–52.
Quanta
2022-11-03
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/202
10.12743/quanta.v11i1.202
Quanta; Vol 11, No 1 (2022); 42-52
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/202/150
Copyright (c) 2022 Quanta
oai:ojs.quanta.ws:article/22
2024-02-05T10:31:41Z
quanta:ART
Is the Quantum State Real? An Extended Review of ψ-ontology Theorems
Leifer, Matthew Saul
Towards the end of 2011, Pusey, Barrett and Rudolph derived a theorem that aimed to show that the quantum state must be ontic (a state of reality) in a broad class of realist approaches to quantum theory. This result attracted a lot of attention and controversy. The aim of this review article is to review the background to the Pusey–Barrett–Rudolph Theorem, to provide a clear presentation of the theorem itself, and to review related work that has appeared since the publication of the Pusey–Barrett–Rudolph paper. In particular, this review: Explains what it means for the quantum state to be ontic or epistemic (a state of knowledge); Reviews arguments for and against an ontic interpretation of the quantum state as they existed prior to the Pusey–Barrett–Rudolph Theorem; Explains why proving the reality of the quantum state is a very strong constraint on realist theories in that it would imply many of the known no-go theorems, such as Bell's Theorem and the need for an exponentially large ontic state space; Provides a comprehensive presentation of the Pusey–Barrett–Rudolph Theorem itself, along with subsequent improvements and criticisms of its assumptions; Reviews two other arguments for the reality of the quantum state: the first due to Hardy and the second due to Colbeck and Renner, and explains why their assumptions are less compelling than those of the Pusey–Barrett–Rudolph Theorem; Reviews subsequent work aimed at ruling out stronger notions of what it means for the quantum state to be epistemic and points out open questions in this area. The overall aim is not only to provide the background needed for the novice in this area to understand the current status, but also to discuss often overlooked subtleties that should be of interest to the experts.Quanta 2014; 3: 67–155.
Quanta
Perimeter Institute for Theoretical Physics
The Foundational Questions Institute (FQXi)
2014-11-05
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/22
10.12743/quanta.v3i1.22
Quanta; Vol 3, No 1 (2014); 67-155
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eng
http://quanta.ws/ojs/index.php/quanta/article/view/22/91
oai:ojs.quanta.ws:article/63
2024-02-05T10:32:20Z
quanta:ART
Quantum Mechanics and Liouville's Equation
Nauenberg, Michael
In non-relativistic quantum mechanics, the absolute square of Schrödinger's wave function for a particle in a potential determines the probability of finding it either at a position or momentum at a given time. In classical mechanics the corresponding problem is determined by the solution of Liouville's equation for the probability density of finding the joint position and momentum of the particle at a given time. Integrating this classical solution over either one of these two variables can then be compared with the probability in quantum mechanics. For the special case that the force is a constant, it is shown analytically that for an initial Gaussian probability distribution, the solution of Liouville's integrated over momentum is equal to Schrödinger's probability function in coordinate space, provided the coordinate and momentum initial widths of this classical solution satisfy the minimal Heisenberg uncertainty relation. Likewise, integrating Lioville's solution over position is equal to Schrödinger's probability function in momentum space.Quanta 2017; 6: 53–56.
Quanta
2017-09-09
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/63
10.12743/quanta.v6i1.63
Quanta; Vol 6, No 1 (2017); 53-56
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/63/96
Copyright (c) 2017 Quanta
oai:ojs.quanta.ws:article/88
2024-02-05T10:32:46Z
quanta:ART
Taming the Delayed Choice Quantum Eraser
Fankhauser, Johannes
I discuss the delayed choice quantum eraser experiment by drawing an analogy to a Bell-type measurement and giving a straightforward account in standard quantum mechanics. The delayed choice quantum eraser experiment turns out to resemble a Bell-type scenario in which the resolution of the paradox is rather trivial, and so there really is no mystery. At first glance, the experiment suggests that measurements on one part of an entangled photon pair (the idler) can be employed to control whether the measurement outcome of the other part of the photon pair (the signal) produces interference fringes at a screen after being sent through a double slit. Significantly, the choice whether there is interference or not can be made long after the signal photon encounters the screen. The results of the experiment have been alleged to invoke some sort of backwards in time influence. I argue that this issue can be eliminated by taking into proper account the role of the signal photon. Likewise, in the de Broglie–Bohm picture the trajectories of the particle can be given a well-defined description at any instant of time during the experiment. Thus, it is again clear that there is no need to resort to any kind of backwards in time influence.Quanta 2019; 8: 44-56.
Quanta
2019-08-11
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/88
10.12743/quanta.v8i1.88
Quanta; Vol 8, No 1 (2019); 44-56
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/88/118
http://quanta.ws/ojs/index.php/quanta/article/downloadSuppFile/88/26
Copyright (c) 2019 Quanta
oai:ojs.quanta.ws:article/174
2024-02-05T10:33:10Z
quanta:ART
George Sudarshan: Perspectives and Legacy
Bhamathi, Gopalakrishnan
George Sudarshan has been hailed as a titan in physics and as one who has made some of the most significant contributions in several areas of physics. This article is an attempt to highlight the seminal contributions he has made in physics and the significant developments that arose from his work.Quanta 2021; 10: 75–104.
Quanta
2021-12-24
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
http://quanta.ws/ojs/index.php/quanta/article/view/174
10.12743/quanta.v10i1.174
Quanta; Vol 10, No 1 (2021); 75-104
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/174/144
Copyright (c) 2021 Quanta
oai:ojs.quanta.ws:article/243
2024-02-05T10:33:31Z
quanta:ART
Monte Carlo Simulation for the Frequency Comb Spectrum of an Atom Laser
Schelle, Alexej
A theoretical particle-number conserving quantum field theory based on the concept of imaginary time is presented and applied to the scenario of a coherent atomic laser field at ultra-cold temperatures. The proposed theoretical model describes the analytical derivation of the frequency comb spectrum for an atomic laser realized from modeling a coherent atomic beam of condensate and non-condensate quantum field components released from a trapped Bose–Einstein condensate at a given repetition phase and frequency. The condensate part of the atomic vapor is assumed to be subjected to thermal noise induced by the temperature of the surrounding thermal atomic cloud. This new quantum approach uses time periodicity and an orthogonal decomposition of the quantum field in a complex-valued quantum field representation to derive and model the quantum field's forward- and backward-propagating components as a standing wave field in the same unique time and temperature domain without quantitative singularities at finite temperatures. The complex-valued atom laser field, the resulting frequency comb, and the repetition frequency distribution with the varying shape of envelopes are numerically monitored within a Monte Carlo sampling method, as a function of temperature and trap frequency of the external confinement.Quanta 2023; 12: 171–179.
Quanta
2023-11-16
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/243
10.12743/quanta.v12i1.243
Quanta; Vol 12, No 1 (2023); 171-179
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/243/165
Copyright (c) 2023 Quanta
oai:ojs.quanta.ws:article/19
2024-02-05T10:31:41Z
quanta:ART
Constructive Empiricism, Partial Structures and the Modal Interpretation of Quantum Mechanics
Bueno, Otávio
Van Fraassen's modal interpretation of non-relativistic quantum mechanics is articulated to support an anti-realist account of quantum theory. However, given the particular form of van Fraassen's anti-realism (constructive empiricism), two problems arise when we try to make it compatible with the modal interpretation: one difficulty concerns the tension between the need for modal operators in the modal interpretation and van Fraassen's skepticism regarding real modality in nature; another addresses the need for the truth predicate in the modal interpretation and van Fraassen's rejection of truth as the aim of science. After examining these two problems, I suggest a formal framework in which they can be accommodated – using da Costa and French's partial structures approach – and indicate a variant of van Fraassen's modal interpretation that does not face these difficulties.Quanta 2014; 3: 1–15.
Quanta
2014-01-15
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/19
10.12743/quanta.v3i1.19
Quanta; Vol 3, No 1 (2014); 1-15
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/19/72
oai:ojs.quanta.ws:article/48
2024-02-05T10:32:07Z
quanta:ART
Weak Measurement and Two-State-Vector Formalism: Deficit of Momentum Transfer in Scattering Processes
Chatzidimitriou-Dreismann, Chariton Aris
The notions of weak measurement, weak value, and two-state-vector formalism provide a new quantum-theoretical frame for extracting additional information from a system in the limit of small disturbances to its state. Here, we provide an application to the case of two-body scattering with one body weakly interacting with an environment. The direct connection to real scattering experiments is pointed out by making contact with the field of impulsive incoherent neutron scattering from molecules and condensed systems. In particular, we predict a new quantum effect in neutron-atom collisions, namely an observable momentum transfer deficit; or equivalently, a reduction of effective mass below that of the free scattering atom. Two corroborative experimental findings are shortly presented. Implications for current and further experiments are mentioned. An interpretation of this effect and the associated experimental results within conventional theory is currently unavailable.Quanta 2016; 5: 61–84.
Quanta
2016-10-28
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/48
10.12743/quanta.v5i1.48
Quanta; Vol 5, No 1 (2016); 61-84
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/48/81
Copyright (c) 2016 Quanta
oai:ojs.quanta.ws:article/82
2024-02-05T10:32:35Z
quanta:ART
How Does Nature Accomplish Spooky Action at a Distance?
Bhaumik, Mani L.
The enigmatic nonlocal quantum correlation that was famously derided by Einstein as "spooky action at a distance" has now been experimentally demonstrated to be authentic. The quantum entanglement and nonlocal correlations emerged as inevitable consequences of John Bell's epochal paper on Bell's inequality. However, in spite of some extraordinary applications as well as attempts to explain the reason for quantum nonlocality, a satisfactory account of how Nature accomplishes this astounding phenomenon is yet to emerge. A cogent mechanism for the occurrence of this incredible event is presented in terms of a plausible quantum mechanical Einstein–Rosen bridge.Quanta 2018; 7: 111–117.
Quanta
2018-12-23
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/82
10.12743/quanta.v7i1.82
Quanta; Vol 7, No 1 (2018); 111-117
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/82/155
Copyright (c) 2018 Quanta
oai:ojs.quanta.ws:article/159
2024-02-05T10:33:10Z
quanta:ART
A Class of Stochastic and Distributions-Free Quantum Mechanical Evolution Equations
Costanza, Gregorio Jose
A procedure allowing to construct rigorously discrete as well as continuum deterministic evolution equations from stochastic evolution equations is developed using Dirac's bra–ket notation. This procedure is an extension of an approach previously used by the author coined Discrete Stochastic Evolution Equations. Definitions and examples of discrete as well as continuum one-dimensional lattices are developed in detail in order to show the basic tools that allow to construct Schrödinger-like equations. Extension to multi-dimensional lattices are studied in order to provide a wider exposition and the one-dimensional cases are derived as special cases, as expected. Some variants of the procedure allow the construction of other evolution equations. Also, using a limiting procedure, it is possible to derive the Schrödinger equation from the Schrödinger-like equations. Another possible approach is given in the appendix.Quanta 2021; 10: 22–33.
Quanta
2021-10-23
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/159
10.12743/quanta.v10i1.159
Quanta; Vol 10, No 1 (2021); 22-33
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/159/131
http://quanta.ws/ojs/index.php/quanta/article/downloadSuppFile/159/35
http://quanta.ws/ojs/index.php/quanta/article/downloadSuppFile/159/36
http://quanta.ws/ojs/index.php/quanta/article/downloadSuppFile/159/37
Copyright (c) 2021 Quanta
oai:ojs.quanta.ws:article/223
2024-02-05T10:33:31Z
quanta:ART
Evaluation of the Feynman Propagator by Means of the Quantum Hamilton-Jacobi Equation
Fusco Girard, Mario
It is shown that the complex phase of the Feynman propagator is a solution of the quantum Hamilton–Jacobi equation, namely, it is the quantum Hamilton's principal function (or quantum action). Therefore, the Feynman propagator can be computed either by means of the path integration, or by the way of the Hamilton–Jacobi equation. This is analogous to what happens in classical mechanics, where the Hamilton's principal function can be computed either by integrating the Lagrangian along the extremal paths, or as a solution of partial differential equation, namely the classical Hamilton–Jacobi equation. If the path is decomposed in the classical one and quantum fluctuations, the contribution of these quantum fluctuations satisfies a non-linear partial differential equation, whose coefficients depend on the classical action. When the contribution of the quantum fluctuations depend only on the time, it can be computed by means of a simple integration. The final results for the propagators in this case are equal to the Van Vleck–Pauli–Morette expressions, even though the two derivations are quite different.Quanta 2023; 12: 22–26.
Quanta
2023-04-24
info:eu-repo/semantics/article
info:eu-repo/semantics/publishedVersion
Peer-reviewed Article
application/pdf
http://quanta.ws/ojs/index.php/quanta/article/view/223
10.12743/quanta.v12i1.223
Quanta; Vol 12, No 1 (2023); 22-26
1314-7374
eng
http://quanta.ws/ojs/index.php/quanta/article/view/223/157
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