Leggett-Garg Inequalities
TLDR
In contrast to the spatial Bell's inequalities, which probe entanglement between spatially-separated systems, the Leggett-Garg inequalities test the correlations of a single system measured at different times as discussed by the authors.Abstract:
In contrast to the spatial Bell's inequalities, which probe entanglement between spatially-separated systems, the Leggett-Garg inequalities test the correlations of a single system measured at different times. Violation of a genuine Leggett-Garg test implies either the absence of a realistic description of the system or the impossibility of measuring the system without disturbing it. Quantum mechanics violates the inequalities on both accounts and the original motivation for these inequalities was as a test for quantum coherence in macroscopic systems. The last few years has seen a number of experimental tests and violations of these inequalities in a variety of microscopic systems such as superconducting qubits, nuclear spins, and photons. In this article, we provide an introduction to the Leggett-Garg inequalities and review these latest experimental developments. We discuss important topics such as the significance of the non-invasive measurability assumption, the clumsiness loophole, and the role of weak measurements. Also covered are some recent theoretical proposals for the application of Leggett-Garg inequalities in quantum transport, quantum biology and nano-mechanical systems.read more
Citations
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Stochastic Processes in Physics and Chemistry
TL;DR: Van Kampen as mentioned in this paper provides an extensive graduate-level introduction which is clear, cautious, interesting and readable, and could be expected to become an essential part of the library of every physical scientist concerned with problems involving fluctuations and stochastic processes.
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Ideal Negative Measurements in Quantum Walks Disprove Theories Based on Classical Trajectories
TL;DR: In this paper, a stringent test of the nonclassicality of the motion of a massive quantum particle propagating on a discrete lattice is presented, which rigorously excludes (i.e., falsifies) any explanation of quantum transport based on classical, well defined trajectories.
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Temporal Quantum Correlations and Leggett-Garg Inequalities in Multilevel Systems
Costantino Budroni,Clive Emary +1 more
TL;DR: It is shown that the quantum bound for temporal correlation in a Leggett-Garg test, analogous to the Tsirelson bound for spatial correlations in a Bell test, strongly depends on the number of levels N that can be accessed by the measurement apparatus via projective measurements.
Journal ArticleDOI
A strict experimental test of macroscopic realism in a superconducting flux qubit
George C. Knee,Kosuke Kakuyanagi,Mao Chuang Yeh,Yuichiro Matsuzaki,Hiraku Toida,Hiroshi Yamaguchi,Shiro Saito,Anthony J. Leggett,William J. Munro +8 more
TL;DR: This work describes and implements an experimental protocol capable of constraining theories of macroscopic realism, that is more noise tolerant and conceptually transparent than the original Leggett–Garg test, and addresses the ‘clumsiness loophole' by determining classical disturbance with control experiments.
Journal ArticleDOI
Weak values as interference phenomena
TL;DR: Weak values arise experimentally as conditioned averages of weak (noisy) observable measurements that minimally disturb an initial quantum state, and also as dynamical variables for reduced quantum state evolution even in the absence of measurement as discussed by the authors.
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