Skip to main content

Research Repository

Advanced Search

Maximum violations of the quantum-witness equality

Schild, Greg; Emary, Clive


Greg Schild

Clive Emary


We consider the quantum-witness test of macroscopic realism and derive an upper bound for possible violations of this equality due to quantum mechanics. The bound depends only on the number of possible outcomes for the blind measurement at the heart of the witness protocol. Mirroring recent results for the related Leggett-Garg inequality, we show that quantum mechanics can saturate the algebraic bound for large systems. We also establish a connection between the quantum witness and the trace distance between density matrices and discuss how the quantum witness can be used to obtain a bound on the Hilbert-space dimension of the system under study.


Schild, G., & Emary, C. (2015). Maximum violations of the quantum-witness equality. Physical review. A, 92(3), 1-6.

Acceptance Date Jul 19, 2015
Online Publication Date Sep 3, 2015
Publication Date Sep 3, 2015
Deposit Date Oct 15, 2015
Publicly Available Date Nov 23, 2017
Journal Physical review A
Print ISSN 1050-2947
Electronic ISSN 1094-1622
Publisher American Physical Society
Peer Reviewed Peer Reviewed
Volume 92
Issue 3
Article Number ARTN 032101
Pages 1-6
Keywords Quantum-witness equality
Public URL
Publisher URL
Additional Information Authors' accepted manuscript of article published in: Physical review A, v.92, issue 3


You might also like

Downloadable Citations