Hannover 2013 – scientific programme

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Q: Fachverband Quantenoptik und Photonik

Q 6: Ultracold atoms and molecules

Q 6.1: Group Report

Monday, March 18, 2013, 11:00–11:30, A 310

Electric quantum walks — •Andrea Alberti, Maximilian Genske, Andreas Steffen, Noomen Belmechri, Wolfgang Alt, and Dieter Meschede — Institut für Angewandte Physik, Universität Bonn - Wegelerstr. 8, 53115 Bonn

Quantum walks represent the quantum motion of a particle on a lattice with a strictly local dynamics, and they constitute the quantum counterpart of classic random walks. Their dynamics is determined by periodically reiterating a set of discrete quantum operations. Single atoms in a spin-dependent optical lattice provide, e.g., spin-dependent displacements, spin rotations, and collisional phase shifts, which can be employed to experimentally implement quantum walks and to simulate the quantum evolution of complex physical systems.

We will report on the experimental realization of an electric quantum walk, which mimics the quantum transport of charged particles in a period potential in the presence of an external electric field. The continuous-time quantum dynamics of these systems -- well known for leading to the Bloch oscillation phenomenon -- is here stroboscopically approximated by a periodic sequence of basic discrete operations.

We are able to reproduce the mechanism of Bloch oscillations and to investigate the Landau-Zener tunneling between the two energy bands that govern the transport dynamics of quantum walks. We detected quantum resonances every time the Bloch period is chosen commensurate with duration of one step, forcing the walker to spread out ballistically. Off-resonance, we present a clear experimental signature that the walker remains localized instead.