Speaker
Description
We report on a stringent test of the nonclassicality of the motion of a massive quantum particle that propagates on a discrete lattice. Measuring temporal correlations of the position of single Cs atoms performing a quantum walk, we observe a 6σ violation of the Leggett-Garg inequality [1]. Our results rigorously exclude (i.e., falsify) any explanation of the motion of a Cs atom based on classical, well-defined trajectories, and indicate instead that the atom must propagate in a superposition of multiple trajectories. For this experimental test, we have devised a new technique to realize ideal negative measurements—namely, the ability to measure a physical object avoiding any direct interaction with it. Interaction-free measurements are a prerequisite for any rigorous LG test, as without it, violations can simply be attributed to an unwitting invasiveness on behalf of the experimenter, rather than to the absence of a realistic description.
In 1993, Elitzur and Vaidman proposed a different setup that exploits interaction-free measurements to detect the presence of an object— in a dramatic scenario, a bomb—without interacting with it. In a recent experiment [2], we have implemented the “bomb test” with a single atom trapped in a spin-dependent optical lattice. We show the relation between the Elitzur-Vaidman bomb tester and Leggett-Garg falsification experiments by demonstrating an experimental violation of the Leggett-Garg inequality by 21σ.
References:
[1] C. Robens, W. Alt, D. Meschede, C. Emary, and A. Alberti, Ideal Negative Measurements in Quantum Walks Disprove Theories Based on Classical Trajectories, Phys. Rev. X 5, 011003 (2015).
[2] C. Robens, W. Alt, C. Emary, D. Meschede, and A. Alberti, Atomic “bomb testing”: the Elitzur–Vaidman experiment violates the Leggett–Garg inequality, Appl. Phys. B 123, 12 (2016).
| Topic: | Mini-workshop: Quantum Foundations and Quantum Information |
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