Compatibility of causal hidden-variable theories with a delayed-choice experiment

Huang, He-Liang; Luo, Yi-Han; Bai, Bing; Deng, Yaohao; Wang, H.; Zhao, Qi; Zhong, Han-Sen; Nie, You-Qi; Jiang, Wenzhe; Wang, Xi-Lin; Zhang, Jun; Li, Li; Liu, Nai-Le; Byrnes, Tim; Dowling, Jonathan P.; Lu, Chao‐Yang; Pan, Jian-Wei

doi:10.1103/physreva.100.012114

Cited by 20 publications

(6 citation statements)

References 30 publications

(39 reference statements)

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“…On the other hand, with the inclusion of an additional phase shift in the MZ interferometer, CLP demonstrated that a two-dimensional classical model would need to be retrocausal to explain the predicted observations, which lead to a violation of a dimension witness inequality. Recent experiments confirm these predictions [27,28]. In their analysis, the meaning of "non-retrocausal" is that, in a model which assumes realism, hidden variables λ associated with the preparation state are independent of any future measurement setting, φ.…”

Section: Introductionmentioning

confidence: 92%

Macroscopic delayed-choice and retrocausality: quantum eraser, Leggett-Garg and dimension witness tests with cat states

Thenabadu,

Reid

2021

Preprint

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We propose delayed choice experiments carried out with macroscopic qubits, realised as macroscopically-distinct coherent states |α and | − α . Quantum superpositions of |α and | − α are created via a unitary interaction U (θ) based on a nonlinear Hamiltonian, in analogy with polarising beam splitters used in photonic experiments. Macroscopic delayed-choice experiments give a compelling reason to develop interpretations not allowing macroscopic retrocausality (MrC). We therefore consider weak macroscopic realism (wMR), which specifies a hidden variable λ θ to determine the macroscopic qubit value (analogous to 'which-way' information), independent of any future measurement setting φ. Using entangled cat states, we demonstrate a quantum eraser where the choice to measure a which-way or wave-type property is delayed. Consistency with wMR is possible, if we interpret the macroscopic qubit value to be determined by λ θ without specification of the state at the level of order , where fringes manifest. We then demonstrate violations of a delayed-choice Leggett-Garg inequality, and of the dimension witness inequality applied to the Wheeler-Chaves-Lemos-Pienaar experiment, where measurements need only distinguish the macroscopic qubit states. This negates all two-dimensional non-retrocausal models, thereby suggesting MrC. However, one can interpret consistently with wMR, thus avoiding conclusions of MrC, by noting extra dimensions, and by noting that the violations require further unitary dynamics U for each system. The violations are then explained as failure of deterministic macroscopic realism (dMR), which specifies validity of λ θ prior to the dynamics U (θ) determining the measurement setting θ. Finally, although there is consistency with wMR for macroscopic observations, we demonstrate Einstein-Podolsky-Rosen-type paradoxes at a microscopic level, based on fringe distributions.

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Section: Introductionmentioning

confidence: 92%

Macroscopic delayed-choice and retrocausality: quantum eraser, Leggett-Garg and dimension witness tests with cat states

Thenabadu,

Reid

2021

Preprint

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“…On the other hand, a modified delayed-choice experiment can lead to a falsification of a subset of weak MR models. The delayed-choice Wheeler–Chaves–Lemos–Pienaar experiment [ 88 , 89 , 90 ] falsifies all two-dimensional non-retrocausal models for a two-state system, described by qubits

. Using the mapping ( 7 ) and considering the unitary rotations

where

is a multiple of

, it is possible to map the microscopic spin experiment involving

onto one involving the macroscopic qubits

[ 81 ].…”

Section: Tests Of Weak Macroscopic Realismmentioning

confidence: 99%

Weak versus Deterministic Macroscopic Realism, and Einstein–Podolsky–Rosen’s Elements of Reality

Fulton,

Thenabadu,

Teh

et al. 2023

Entropy

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The violation of a Leggett–Garg inequality confirms the incompatibility between quantum mechanics and the combined premises (called macro-realism) of macroscopic realism (MR) and noninvasive measurability (NIM). Arguments can be given that the incompatibility arises because MR fails for systems in a superposition of macroscopically distinct states—or else, that NIM fails. In this paper, we consider a strong negation of macro-realism, involving superpositions of coherent states, where the NIM premise is replaced by Bell’s locality premise. We follow recent work and propose the validity of a subset of Einstein–Podolsky–Rosen (EPR) and Leggett–Garg premises, referred to as weak macroscopic realism (wMR). In finding consistency with wMR, we identify that the Leggett–Garg inequalities are violated because of failure of both MR and NIM, but also that both are valid in a weaker (less restrictive) sense. Weak MR is distinguished from deterministic macroscopic realism (dMR) by recognizing that a measurement involves a reversible unitary interaction that establishes the measurement setting. Weak MR posits that a predetermined value for the outcome of a measurement can be attributed to the system after the interaction, when the measurement setting is experimentally specified. An extended definition of wMR considers the “element of reality” defined by EPR for system A, where one can predict with certainty the outcome of a measurement on A by performing a measurement on system B. Weak MR posits that this element of reality exists once the unitary interaction determining the measurement setting at B has occurred. We demonstrate compatibility of systems violating Leggett–Garg inequalities with wMR but point out that dMR has been shown to be falsifiable. Other tests of wMR are proposed, the predictions of wMR agreeing with quantum mechanics. Finally, we compare wMR with macro-realism models discussed elsewhere. An argument in favour of wMR is presented: wMR resolves a potential contradiction pointed out by Leggett and Garg between failure of macro-realism and assumptions intrinsic to quantum measurement theory.

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“…Besides the applications to quantum metrology and in general to quantum information tasks, a MZI can be also the testbed for foundational tests, like those exploring waveparticle duality of photons [256][257][258][259][260][261][262][263][264] or even quantum gravity phenomena when the probes are massive systems [265][266][267] .…”

Section: A Phase Estimation Problemmentioning

confidence: 99%

Photonic Quantum Metrology

Polino¹,

Valeri²,

Spagnolo³

et al. 2020

Preprint

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Quantum Metrology is one of the most promising application of quantum technologies. The aim of this research field is the estimation of unknown parameters exploiting quantum resources, whose application can lead to enhanced performances with respect to classical strategies. Several physical quantum systems can be employed to develop quantum sensors, and photonic systems represent ideal probes for a large number of metrological tasks. Here we review the basic concepts behind quantum metrology and then focus on the application of photonic technology for this task, with particular attention to phase estimation. We describe the current state of the art in the field in terms of platforms and quantum resources. Furthermore, we present the research area of multiparameter quantum metrology, where multiple parameters have to be estimated at the same time. We conclude by discussing the current experimental and theoretical challenges, and the open questions towards implementation of photonic quantum sensors with quantum-enhanced performances in the presence of noise.

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Compatibility of causal hidden-variable theories with a delayed-choice experiment

Cited by 20 publications

References 30 publications

Macroscopic delayed-choice and retrocausality: quantum eraser, Leggett-Garg and dimension witness tests with cat states

Macroscopic delayed-choice and retrocausality: quantum eraser, Leggett-Garg and dimension witness tests with cat states

Weak versus Deterministic Macroscopic Realism, and Einstein–Podolsky–Rosen’s Elements of Reality

Photonic Quantum Metrology

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