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Leggett-Garg inequalities

Emary, Clive; Lambert, Neill; Nori, Franco


Clive Emary

Neill Lambert

Franco Nori


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.

Journal Article Type Article
Publication Date Jan 1, 2014
Journal Reports on Progress in Physics
Print ISSN 0034-4885
Electronic ISSN 1361-6633
Publisher IOP Publishing
Peer Reviewed Peer Reviewed
Volume 77
Issue 1
Article Number 016001
APA6 Citation Emary, C., Lambert, N., & Nori, F. (2014). Leggett-Garg inequalities. Reports on progress in physics, 77(1), doi:10.1088/0034-4885/77/1/016001
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Copyright Statement ©2018 The authors


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