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Physical Review A

Breakdown of classical conservation of energy in a quantum wave-packet collision with a double barrier

A. L. Pérez Prieto, S. Brouard, Juan Gonzalo Muga

Published Jan 6, 2005• 5 citations
Publisher

Abstract

A transient interference during the collision of a broad quantum particle wave packet with a properly chosen potential barrier suppresses, for energies well above the barrier top, the main incident momentum. This collision enhances the momenta below and above the central one, violating the classical conservation of energy. For the double square barrier the effect is due to the interference between three components (incident, transmitted, and interbarriers terms) and survives much longer than for the single barrier, facilitating its observation. A quantum optical realization with two-level atoms and effective laser barriers is discussed.

DOI
10.1103/physreva.71.012703

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A transient interference during the collision of a broad quantum particle wave packet with a properly chosen potential barrier suppresses, for energies well above the barrier top, the main incident momentum. This collision enhances the momenta below and above the central one, violating the classical conservation of energy. For the double square barrier the effect is due to the interference between three components (incident, transmitted, and interbarriers terms) and survives much longer than for the single barrier, facilitating its observation. A quantum optical realization with two-level atoms and effective laser barriers is discussed.
Due to a transient quantum interference during a wave packet collision with a potential barrier, a particular momentum, that depends on the potential parameters, but is close to the initial average momentum, becomes suppressed. The hole left pushes the momentum distribution outwards leading to a significant constructive enhancement of lower and higher momenta. This is explained in the momentum complex-plane language in terms of a saddle point and two contiguous ``structural'' poles, which are not associated with resonances but with incident and transmitted components of the wave function.
The propagation of a two-level atomic wave packet across a laser beam is considered. For small incident kinetic energies of the atom, the wave nature of the center-of-mass motion becomes apparent, giving reflections and refractions in the case of a square profile of the laser beam. When the incident momentum is low enough, we show that one of the dressed states cannot propagate inside the laser beam, giving rise to an evanescent atomic wave packet. Also a stopped excited component is found when the incident momentum equals in modulus---not in direction---the one-photon recoil. \textcopyright{} 1996 The American Physical Society.