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Ambiguous measurements, signaling, and violations of Leggett-Garg inequalities

Emary, Clive


Clive Emary


Ambiguous measurements do not reveal complete information about the system under test. Their quantum-mechanical counterparts are semiweak (or in the limit, weak) measurements and here we discuss their role in tests of the Leggett-Garg inequalities. We show that, while ambiguous measurements allow one to forgo the usual noninvasive measurability assumption, to derive a Leggett-Garg inequality that may be violated, we are forced to introduce another assumption that equates the invasive influence of ambiguous and unambiguous detectors. Based on this assumption, we derive signaling conditions that should be fulfilled for the plausibility of the Leggett-Garg test. We then propose an experiment on a three-level system with a direct quantum-optics realization that satisfies all signaling constraints and violates a Leggett-Garg inequality.


Emary, C. (2017). Ambiguous measurements, signaling, and violations of Leggett-Garg inequalities. Physical Review A, 96(4), Article 042102.

Journal Article Type Article
Acceptance Date Apr 2, 2016
Online Publication Date Oct 4, 2017
Publication Date Oct 4, 2017
Deposit Date Jun 28, 2018
Publicly Available Date Oct 27, 2022
Journal Physical Review A
Print ISSN 2469-9926
Electronic ISSN 2469-9934
Publisher American Physical Society
Peer Reviewed Peer Reviewed
Volume 96
Issue 4
Article Number 042102
Public URL
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