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arXiv:quant-ph/0309149 · Physical Review Letters

Directed Motion for Delta-Kicked Atoms with Broken Symmetries: Comparison between Theory and Experiment

Philip H. Jones, M. Goonasekera, D. R. Meacher, Thibaut Jonckheere, T. S. Monteiro

Published Feb 14, 2007• 66 citations
arXivHTMLPDF

Abstract

We report an experimental investigation of momentum diffusion in the delta-function kicked rotor where time symmetry is broken by a two-period kicking cycle and spatial symmetry by an alternating linear potential. We exploit this, and a technique involving a moving optical potential, to create an asymmetry in the momentum diffusion that is due to the classical chaotic diffusion. This represents a realization of a type of Hamiltonian quantum ratchet.

DOI
10.1103/physrevlett.98.073002

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We report an experimental investigation of momentum diffusion in the delta-function kicked rotor where time symmetry is broken by a two-period kicking cycle and spatial symmetry by an alternating linear potential. We exploit this, and a technique involving a moving optical potential, to create an asymmetry in the momentum diffusion that is due to the classical chaotic diffusion. This represents a realization of a type of Hamiltonian quantum ratchet.
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We report the first direct experimental realization of the quantum $\ensuremath{\delta}$-kicked rotor. Our system consists of a dilute sample of ultracold sodium atoms in a periodic standing wave of near-resonant light that is pulsed on periodically in time to approximate a series of delta functions. Momentum spread of the atoms increases diffusively with every pulse until the "quantum break time" after which exponentially localized distributions are observed. Quantum resonances are found for specific values of the pulse period.
We report on an experimental realization of unidirectional transporting island structures in an otherwise chaotic phase space of the $\ensuremath{\delta}$-kicked rotor system. Using a Bose-Einstein condensate as a source of ultracold atoms, we employ asymmetric phase modulation in the kicks, with the narrow momentum distribution of the atoms allowing us to address individual island structures. We observe quantum ratchet behavior in this system, with clear directed momentum current in the absence of a directional force, which we characterize and connect to $\ensuremath{\epsilon}$-classical theory.
Scope and Method of Study: The purpose of this research was to experimentally study quantum dynamics of systems whose classical dynamics are chaotic. Quantum delta-kicked systems such as kicked rotor and kicked accelerator were used. The cold non condensed atoms were kicked first to realize the kicked accelerator. Among the objectives were the realization of resonances of the kicked accelerator and associated phenomena of quantum accelerator modes using a Bose-Einstein Condensation (BEC). One of the major achievements of the work in this thesis was the creation of the quantum delta-kicked rotor and its associated resonances to realize a quantum ratchet. The properties of the ratchet were studied in detail.