Can different quantum state vectors correspond to the same physical state? An experimental test

Nigg, Daniel; Monz, Thomas; Schindler, Philipp; Martinez, Emanuel Ricardo Monteiro; Hennrich, Markus; Blatt, R.; Pusey, Matthew F.; Rudolph, Terry; Barrett, Jonathan

doi:10.1088/1367-2630/18/1/013007

Cited by 71 publications

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References 34 publications

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“…Notably, Pusey, Barrett, and Rudolph showed that no ψ-epistemic models satisfying some natural independence condition for composite systems can reproduce quantum predictions [3]. A number of other no-go theorems have since been proven, under various assumptions [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. Explicit ψ-epistemic models have nevertheless been constructed for quantum measurement statistics in Hilbert spaces of any dimension [14,19], which get around the assumptions of these no-go theorems.…”

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Howψ-Epistemic Models Fail at Explaining the Indistinguishability of Quantum States

Branciard

2014

Phys. Rev. Lett.

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We study the extent to which ψ-epistemic models for quantum measurement statistics-models where the quantum state does not have a real, ontic status-can explain the indistinguishability of nonorthogonal quantum states. This is done by comparing the overlap of any two quantum states with the overlap of the corresponding classical probability distributions over ontic states in a ψ-epistemic model. It is shown that in Hilbert spaces of dimension d ≥ 4, the ratio between the classical and quantum overlaps in any ψ-epistemic model must be arbitrarily small for certain nonorthogonal states, suggesting that such models are arbitrarily bad at explaining the indistinguishability of quantum states. For dimensions d = 3 and 4, we construct explicit states and measurements that can be used experimentally to put stringent bounds on the ratio of classical-to-quantum overlaps in ψ-epistemic models, allowing one in particular to rule out maximally ψ-epistemic models more efficiently than previously proposed.Despite its central role, the quantum state remains one of the most mysterious objects of quantum theory. Does it correspond to any physical reality, or does it merely represent one's information on a quantum system? These questions have triggered intense debates among physicists and philosophers since the advent of quantum theory, and are still the subject of active research in the study of quantum foundations.The general framework of ontological models [1] proposes a rigorous approach to address such questions. This framework presupposes the existence of underlying states of physical reality-ontic states-and describes the quantum state as a state of knowledge-an epistemic stateabout the actual ontic state of a given quantum system, represented by a probability distribution over the set of ontic states. A fundamental distinction is made between so-called ψ-ontic models, in which any underlying ontic state determines the quantum state uniquely, and socalled ψ-epistemic models, where the same ontic state can be compatible with different quantum states; i.e., the probability distributions corresponding to two different quantum states can overlap. In the former case, the ontic state "encodes" the quantum state, which can hence be understood as a physical property of the system, while in the latter case the quantum state cannot be given the status of a real physical property.The epistemic view of the quantum state is quite attractive, as it gives a natural explanation to many puzzling quantum phenomena [2]-including, for instance, the collapse of the wave function, or the impossibility to perfectly distinguish nonorthogonal quantum states. However, it has been shown that ψ-epistemic models must be severely constrained if they are to reproduce the statistics of quantum measurements. Notably, Pusey, Barrett, and Rudolph showed that no ψ-epistemic models satisfying some natural independence condition for composite systems can reproduce quantum predictions [3]. A number of other no-go theorems have since been proven, under various a...

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Howψ-Epistemic Models Fail at Explaining the Indistinguishability of Quantum States

Branciard

2014

Phys. Rev. Lett.

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“…Indeed, the best such a Bell-local model can do is to satisfy three of the four. An easy way to see the contradiction is by multiplying all four equations, such that the left-hand side is a product of squares, which must be +1, while the right-hand side equals −1 [81]. Using instead a shared a GHZ-state 1 2 ( 000⟩ + 111⟩), to generate the outputs as the results of measurements of σ x (for input 0) and σ y (for input 1), all four requirements ideally satisfied exactly.…”

Section: Ghz Paradox and Multipartite Entanglementmentioning

confidence: 99%

Section: Ghz Paradox and Multipartite Entanglementmentioning

confidence: 99%

“…A violation could instead be obtained from measurements on a statistical mixture of bipartite entangled states with a classically correlated third particle [83]. To demonstrate genuine tripartite Bell-nonlocality, Svetlichny derived an inequality that cannot 76 be violated by any states that are only bipartite entangled [81,83,84](3.14)This inequality can be interpreted as a frustrated network of correlations [83]. In the case where Charlie's input is 0, Alice and Bob play the CHSH game, while for 1 they play the CHSH' game (with reversed inputs) [85].…”

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“…Instead the experiment can merely establish bounds on the absolute value of the classical overlap in ψ-epistemic models that satisfy preparation independence. This argument has allowed to experimentally rule out maximally ψ-epistemic models under the assumption of preparation independence [81]. …”

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Exploring quantum foundations with single photons

Ringbauer¹

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Quantum mechanics is our most successful physical theory and has been confirmed to extreme accuracy, yet, a century after its inception it is still unclear what it says about the nature of reality. In this thesis, I explore some of the foundational questions which are central to our understanding of quantum mechanics using single photons as an experimental platform. Three experiments form the core of the thesis, studying, respectively, the role of reality, causality, and uncertainty in quantum mechanics. These experiments shed light on decade-old questions that have previously been thought to be outside the realm of experimental physics. The results contribute to our understanding of the structure of quantum mechanics, and reveal novel aspects of phenomena that were believed to be well understood. In three further experiments I also touch upon the topics of finding physical principles behind quantum mechanics, quantum effects in extreme gravitational fields, and developing a pathway towards tests of macroscopic quantum phenomena. Starting out as a fringe discipline, the field of quantum foundations has developed into an influential area of research. It is now becoming possible to turn many of the foundational questions in quantum mechanics from topics of philosophy into topics of physics. Subjecting these questions to rigorous experimental tests the field is making progress in the quest for understanding our best physical theory.i Declaration by authorThis thesis is composed of my original work, and contains no material previously published or written by another person except where due reference has been made in the text. I have clearly stated the contribution by others to jointly-authored works that I have included in my thesis.I have clearly stated the contribution of others to my thesis as a whole, including statistical assistance, survey design, data analysis, significant technical procedures, professional editorial advice, and any other original research work used or reported in my thesis. The content of my thesis is the result of work I have carried out since the commencement of my research higher degree candidature and does not include a substantial part of work that has been submitted to qualify for the award of any other degree or diploma in any university or other tertiary institution. I have clearly stated which parts of my thesis, if any, have been submitted to qualify for another award.I acknowledge that an electronic copy of my thesis must be lodged with the University Library and, subject to the policy and procedures of The University of Queensland, the thesis be made available for research and study in accordance with the Copyright Act 1968 unless a period of embargo has been approved by the Dean of the Graduate School.I acknowledge that copyright of all material contained in my thesis resides with the copyright holder(s) of that material. Where appropriate I have obtained copyright permission from the copyright holder to reproduce material in this thesis.ii Publications during candidaturePeer-re...

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Underlying non‐Hermitian character of the Born rule in open quantum systems

García–Calderón

Chaos-Cador

2016

Fortschritte der Physik

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The absolute value squared of the probability amplitude corresponding to the overlap of an initial state with a continuum wave solution to the Schrödinger equation of the problem, has the physical interpretation provided by the Born rule. Here, it is shown that for an open quantum system, the above probability may be written in an exact analytical fashion as an expansion in terms of the non‐Hermitian resonance (quasinormal) states and complex poles to the problem which provides an underlying non‐Hermitian character of the Born rule.

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Can different quantum state vectors correspond to the same physical state? An experimental test

Cited by 71 publications

References 34 publications

Howψ-Epistemic Models Fail at Explaining the Indistinguishability of Quantum States

Howψ-Epistemic Models Fail at Explaining the Indistinguishability of Quantum States

Exploring quantum foundations with single photons

Underlying non‐Hermitian character of the Born rule in open quantum systems

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