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

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

Abstract

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.

Citation

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. https://doi.org/10.1103/PhysRevX.5.011003

• 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
• DOI: https://doi.org/10.1103/PhysRevX.5.011003
• Public URL: https://hull-repository.worktribe.com/output/898435
• Publisher URL: https://journals.aps.org/prx/abstract/10.1103/PhysRevX.5.011003