周期驱动产生的均匀费米气体中的不加热
Absence of heating in a uniform Fermi gas created by periodic driving
摘要：
超冷原子气体为探索多体物理提供了有用的工具。这个实验工具箱最近增加的一个是Floquet工程，其中周期性调制的哈密顿量允许创建有效的潜力，否则不存在。然而，当受到外部调制时，一般的相互作用多体系统吸收能量，从而造成加热问题，可能会损害这种方法的有用性。对于具有有界局部能量的离散系统，先前已经观察到随驱动频率呈指数抑制的加热速率，使得系统在极长的持续时间内处于预热状态。但是对于连续空间中的系统，情况仍然不清楚。在这里，我们表明，Floquet工程可以采用强相互作用的简并费米气体保持在一个平坦的盒状电位，而不会引起过度加热的实验相关的时间尺度。该驱动消除了源自两种不同自旋状态的同时磁悬浮的自旋相关电势的影响。我们计算的加热速率，并获得与驱动频率的幂律抑制。为了进一步测试被驱动气体的多体行为，我们测量了在么正性下的对凝聚分数和跨BEC-BCS交叉的接触参数。在低驱动频率下，冷凝物分数被时间相关力减少，但在较高频率下，它恢复并达到比没有驱动时更高的值。我们的研究结果是有希望的外来多体相位的大块强相互作用费米气体与动态工程哈密顿的未来探索。
英文摘要：
Ultracold atomic gas provides a useful tool to explore many-body physics. One of the recent additions to this experimental toolbox is the Floquet engineering, where periodic modulation of the Hamiltonian allows the creation of effective potentials that do not exist otherwise. When subject to external modulations, however, generic interacting many-body systems absorb energy, thus posing a heating problem that may impair the usefulness of this method. For discrete systems with bounded local energy, an exponentially suppressed heating rate with the driving frequency has been observed previously, leaving the system in a prethermal state for exceedingly long durations. But for systems in continuous space, the situation remains unclear. Here we show that Floquet engineering can be employed to a strongly interacting degenerate Fermi gas held in a flat box-like potential without inducing excessive heating on experimentally relevant timescales. The driving eliminates the effect of a spin-dependent potential originating from a simultaneous magnetic levitation of two different spin states. We calculate the heating rate and obtain a power-law suppression with the drive frequency. To further test the many-body behavior of the driven gas, we measure both the pair-condensation fraction at unitarity and the contact parameter across the BEC-BCS crossover. At low driving frequencies, the condensate fraction is reduced by the time-dependent force, but at higher frequencies, it revives and attains an even higher value than without driving. Our results are promising for future exploration of exotic many-body phases of a bulk strongly-interacting Fermi gas with dynamically engineered Hamiltonians.
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