Experimental violations of Leggett-Garg inequalities up to the algebraic maximum for a photonic qubit

Wang, Kunkun; Xu, Mengyan; Liu, Xiao; Xue, Peng

doi:10.1103/physreva.102.022214

Cited by 5 publications

(2 citation statements)

References 25 publications

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“…In addition, the range of such tests can be presented as a hierarchy of temporal correlations [21][22][23][24]. Furthermore, many significant experiments have been implemented in different systems, such as photons [25][26][27][28], superconducting qubits [15,[29][30][31][32][33], and atoms [34,35]. Recently, temporal quantum correlations (including LGI) have found applications for quantum information and communication problems, like witnessing the dimension of a system [36][37][38], the certification of quantum memory [39][40][41][42][43], enhancing the quantumness of a system with non-Markovianity [44], and verifying the quantumness of a channel [45][46][47][48][49].…”

Section: Introductionmentioning

confidence: 99%

Hidden nonmacrorealism: reviving the Leggett-Garg inequality with stochastic operations

Ku,

Weng,

Shih

et al. 2021

Preprint

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The Leggett-Garg inequality (LGI) distinguishes nonmacrorealistic channels from macrorealistic ones by constraining the experimental outcomes of the underlying system. In this work, we propose a class of the channels which, initially, cannot violate LGI (in the form of the temporal Bell inequality) but can violate it after the application of stochastic pre-and post-operations (SPPOs). As a proof-of-principle experiment, we demonstrate the stochastic pre-and post-operations in an amplitude-damping channel with photonic qubits. We denote the above phenomenon as hidden nonmacrorealistic channels. We also discuss the relationship between this hidden nonmacrorealistic channels (in terms of the temporal Clauser-Horne-Shimony-Holt (CHSH) inequality) and the strongly nonlocality-breaking channel, which breaks the hidden spatial CHSH nonlocality for arbitrary states. In general, if the channel satisfies hidden nonmacrorealism, it is not a strongly CHSH nonlocality-breaking channel.

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Section: Introductionmentioning

confidence: 99%

Hidden nonmacrorealism: reviving the Leggett-Garg inequality with stochastic operations

Ku,

Weng,

Shih

et al. 2021

Preprint

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“…1a. It should be noted that, in the Hermitian quantum case, K 3 beyond the Lüders bound can be observed by devising delicate modifications to the standard Leggett-Garg test scenario, such as introducing multi-time correlation functions [27], or using multi-projector measurements [28][29][30][31]. Here, in the framework of the standard test scenario, we focus on the non-Hermitian enhancement of TQCs.…”

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confidence: 99%

Non-Hermitian quantum correlations in the time domain: well beyond Luders bound

Chen,

Wu,

Zhang

et al. 2023

Preprint

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The powerful ability of achieving and manipulating strong spatial quantum correlations has helped the emergence of quantum information science. In contrast, strong temporal quantum correlations (TQC), playing an essential role in a wide range of physical and biological processes, have remained an elusive and long-standing challenge, hindering their practical applications. Here, for the first time, we experimentally demonstrate how to break the Lüders bound and to achieve the ultimate upper limit of TQC, by using a parity-time (PT)-symmetric single-ion system, within a standard measurement scenario. We achieve this goal by approaching an exceptional point (EP) in such a system, confirming the power of PT symmetry and non-Hermitian phase transition in enhancing purely quantum effects. Our work not only removes an important obstacle for TQC-based quantum engineering applications, but also sheds new light on operating quantum devices at EPs.

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