Journal
PHYSICAL REVIEW X
Volume 5, Issue 1, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevX.5.011003
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Funding
- NRW-Nachwuchsforschergruppe Quantenkontrolle auf der Nanoskala
- ERC grant DQSIM
- EU project SIQS
- Alexander von Humboldt Foundation
- BCGS program
- Studienstiftung des deutschen Volkes
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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-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. Here, we employ the witness to discriminate different types of walks spanning from merely classical to wholly quantum dynamics.
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