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arXiv:1604.04277 · New Journal of Physics

Cooling quantum gases with entropy localization

F. Nur Ünal, Erich J. Mueller

Published Feb 6, 2017• 2 citations
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Abstract

We study the dynamics of entropy in a time dependent potential and explore how disorder influences this entropy flow.We show that disorder can trap entropy at the edge of the atomic cloud enabling a novel cooling method.We demonstrate the feasibility of our cooling technique by analyzing the evolution of entropy in a one-dimensional Fermi lattice gas with a time dependent superlattice potential.

DOI
10.1088/1367-2630/aa5e7b

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We investigate a species selective cooling process of a trapped SU(N)\mathrm{SU}(N)SU(N) Fermi gas using entropy redistribution during adiabatic loading of an optical lattice. Using high-temperature expansion of the Hubbard model, we show that when a subset NA<N{N}_{A}<NNA​<N of the single-atom levels experiences a stronger trapping potential in a certain region of space, the dimple, it leads to improvement in cooling as compared to an SU(NA)\mathrm{SU}({N}_{A})SU(NA​) Fermi gas only. We show that optimal performance is achieved when all atomic levels experience the same potential outside the dimple and we quantify the cooling for various NA{N}_{A}NA​ by evaluating the dependence of the final entropy densities and temperatures as functions of the initial entropy. Furthermore, considering 87Sr^{87}\mathrm{Sr}87Sr and 173Yb^{173}\mathrm{Yb}173Yb for specificity, we provide a quantitative discussion of how the state selective trapping can be achieved with readily available experimental techniques.
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We present a framework for local quantum cooling that can be efficiently applied to large-scale Fermi systems. The method introduces local Hermitian operators as a cooling potential while strictly preserving the unitarity of time evolution. Our formulation scales favorably with system size and can be seamlessly integrated into time-dependent density-functional theory frameworks. We demonstrate that energy cooling arises from the damping of particle currents and pairing-field fluctuations. Furthermore, we develop a variant of the scheme that allows the particle number to vary in time, enabling controlled density scans. The method is generic and versatile, as illustrated by applications to spin-imbalanced unitary Fermi gases and to nuclear matter in the neutron-star crust. The framework can be naturally extended to include stochastic noise, providing a foundation for studying thermalization in strongly interacting Fermi superfluids.