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Ideal negative measurements in quantum walks disprove theories based on classical trajectories

Robens, Carsten; Alt, Wolfgang; Meschede, Dieter; Emary, Clive; Alberti, Andrea


Carsten Robens

Wolfgang Alt

Dieter Meschede

Clive Emary

Andrea Alberti


We report on a stringent test of the nonclassicality of the motion of a massive quantum particle, which propagates on a discrete lattice. Measuring temporal correlations of the position of single atoms performing a quantum walk, we observe a 6σ violation of the Leggett-Garg inequality. Our results rigorously excludes (i.e., falsifies) any explanation of quantum transport based on classical, well-defined trajectories. We use so-called ideal negative measurements-an essential requisite for any genuine Leggett-Garg test-to acquire information about the atom's position, yet avoiding any direct interaction with it. The interactionfree measurement is based on a novel atom transport system, which allows us to directly probe the absence rather than the presence of atoms at a chosen lattice site. Beyond the fundamental aspect of this test, we demonstrate the application of the Leggett-Garg correlation function as a witness of quantum superposition. Here, we employ the witness to discriminate different types of walks spanning from merely classical to wholly quantum dynamics.


Robens, C., Alt, W., Meschede, D., Emary, C., & Alberti, A. (2015). Ideal negative measurements in quantum walks disprove theories based on classical trajectories. Physical Review X, 5(1), Article 011003.

Journal Article Type Article
Acceptance Date Nov 13, 2014
Online Publication Date Jan 20, 2015
Publication Date Jan 1, 2015
Deposit Date Jun 28, 2018
Publicly Available Date Jul 19, 2018
Journal Physical Review X
Electronic ISSN 2160-3308
Publisher American Physical Society
Peer Reviewed Peer Reviewed
Volume 5
Issue 1
Article Number 011003
Public URL
Publisher URL


Article (525 Kb)

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Copyright Statement
This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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