@article{2015-robens-alberti-phys-rev-x-fe-in-phy-v5-p011003,
	Abstract = {<p>
	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 6&sigma; 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&mdash;an essential requisite for any genuine Leggett-Garg test&mdash;to acquire information about the atom&rsquo;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. Here, we employ the witness to discriminate different types of walks spanning from merely classical to wholly quantum dynamics.</p>},
	Author = {Robens, C. AND Alt, W. AND Meschede, D. AND Emary, C. AND Alberti, A.},
	Journal = {Phys. Rev. X (Featured in Physics)},
	Pages = {011003},
	Title = {{Ideal Negative Measurements in Quantum Walks Disprove Theories Based on Classical Trajectories}},
	Volume = {5},
	Year = {2015}
}