Ballistic atom pumps

Abstract

We examine a classically-chaotic system consisting of two reservoirs of particles connected by a channel containing oscillating potential-energy barriers. We investigate whether such a system can preferentially pump particles from one reservoir to the other, a process often called "quantum pumping." We show how to make a "particle diode" which under specified conditions permits net particle pumping in only one direction. Then we examine systems having symmetric barriers. We find that if all initial particle energies are considered, a system with symmetric barriers cannot preferentially pump particles. However, if only finite initial energy bands are considered, the system can create net particle transport in either direction. We study the system classically, semiclassically, and quantum mechanically, and find that the quantum description cannot be fully understood without the insight gained from classical and semiclassical analysis.

Matter, energy, and heat transfer in a classical ballistic atom pump

“…We examine the classical scattering of equal numbers of particles which approach such pumps from each reservoir with equal and fixed incident energy. It has been shown that flows may be zero or negligible in pumps with idealized limits such as delta-function barriers or uniform phase-space density [4,26]. Here we show that under more realistic conditions, such pumps can generate significant net transfer of both matter and energy.…”

“…Summary of results: In previous papers [26,30,31] we have shown that two-barrier pumps have the following properties when at least one barrier oscillates. (1) These so-called "quantum pumps" provide nice models of classical chaotic scattering, and their behavior is governed by a heteroclinic tangle.…”

“…System We will establish properties (A)-(D) by examining one specific pump: a particle diode consisting of two Gaussian-shaped potential barriers, only one of which oscillates. We choose this pump as our example because the dynamics of the system become much more complicated when both barriers oscillate [26]. However, allowing the second barrier to oscillate (or changing the barrier parameters) only affects the conclusions discussed below quantitatively.…”

Dynamical resonances and stepped current in an attractive quantum pump

“…The difference between classical and quantum dynamics is clearly magnified by the use of a well potential, and hence this can be a useful system to examine the interface and crossover between quantum and classical dynamics, as well as in the study of quantum chaos [35]. Well-based pumps clearly have much richer dynamics, and therefore, more complicated variations like a turnstile [6,34] would be interesting to examine in future works, particularly in regards to if and how the single-mode dynamical features are manifest in the context of multimode fermionic systems.…”

“…A series of studies [33][34][35][36][37] afterwards revealed that in this approach, the underlying scattering dynamics by a time-varying potential can be studied in its own right replete with rich features that include signatures of chaos, fractal structures, counterintuitive flow and offering, via semiclassical analysis, a fertile system for examining the interface between quantum and classical dynamics. This current study is aligned with these latter developments in the context of ultracold atoms, where the focus is on the details of the scattering dynamics involved rather than on the generation of net directed flow.…”