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A: Fachverband Atomphysik

A 6: Ultracold Atoms, Ions and Molecules II (with Q)

A 6.4: Vortrag

Montag, 29. Februar 2016, 15:15–15:30, e001

Quantum Walks with Neutral Atoms: A look into the motion of a quantum particle — Carsten Robens, Stefan Brakhane, Wolfgang Alt, Dieter Meschede, and •Andrea Alberti — Institut für Angewandte Physik, Universität Bonn – Wegelerstr. 8, 53115 Bonn

I will present quantum walk experiments performed with neutral atoms in spin-dependent optical lattices. A cesium atom with two long-lived internal states behaves like a pseudo spin-1/2 particle. Depending on its spin state, the atom moves at regular time steps either one site to the left or to the right, delocalizing over multiple quantum paths. In the limit of vanishing lattice constant, its quantum behavior is described by the one-dimensional Dirac equation. We have recently developed a new spin-dependent transport system, which allows us to spin-selectively shift only one spin species at a time by an arbitrary number of lattice sites. The new atom transport system allows us to carry out interaction-free measurements of the atom’s position, which we used to exclude (i.e., falsify) any explanation of quantum transport based on classical, well-defined trajectories [1]. To put it into perspective, our experiment represents the most massive test of quantum superposition states that has been hitherto performed based on the stringent, objective criteria provided by the Leggett-Garg inequality.
[1] C. Robens et al. Ideal Negative Measurements in Quantum Walks Disprove Theories Based on Classical Trajectories, Phys. Rev. X 5, 011003 (2015).