2014/04/30 by Carsten Robens, Wolfgang Alt, Dieter Meschede +2 · 1 citation
Physics and Astronomy · #quant-ph
paper · pdf · doi:10.1103/physrevx.5.011003
published as Phys. Rev. X 5, 011003 (2015) · 10 pages, 4 figures
arxiv created 2015/02/10 · arxiv updated 2015/02/11
We report on a stringent test of the non-classicality 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 interaction-free 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. We here employ the witness to discriminate different types of walks spanning from merely classical to wholly quantum dynamics.