Friction in quantum thermodynamics results from fast driving schemes that generate nonadiabatic excitations.

Fermionic superradiance: Placing an atomic gas inside an optical cavity can have profound effects, for example, inducing long-range atomic interactions through the coupling with the cavity’s photons. Such experiments have been done with bosonic atoms but realizing them with fermions has proven trickier. Zhang et al . placed an ultracold gas of fermionic lithium-6 atoms in a cavity pumped by a laser beam orthogonal to the cavity axis. For sufficiently strong pumping, the researchers detected a checkerboard pattern in the atoms’ momentum space corresponding to a superradiant phase transition in the cavity. The Pauli exclusion principle, which applies to fermions but not bosons, slowed down the atomic dynamics. —JS

Understanding nonequilibrium dynamics of strongly interacting quantum systems represents one of the most challenging problems in many‐body physics. Here, quantum thermalization dynamics are explored in real‐time in an ultracold Fermi gas suddenly quenched to the BEC‐BCS crossover. When quenched to unitarity, it is observed that the cloud size remains unchanged in the early evolution while the momentum distribution emerges two prethermal states with a lifetime difference of two orders of magnitude in the early and intermediate stage before very slowly evolving to the final stationary state. It is revealed that a crossover momentum, at which the momentum distribution remains nearly unchanged, is determined by the thermal wavelength at high temperatures and the Fermi momentum while at low temperatures. It is identified that the universal prethermal dynamics scaling where momentum distributions with different temperatures collapse onto one curve. When quenched to the BEC side, the thermalization rapidly relaxes into a prethermal state and exhibits the low energy oscillation related to the molecular bound states. This work provides benchmarks for the study of quantum thermalization in strongly interacting fermionic many‐body systems.

在冷原子研究中,通常采用吸收成像的方式来进行冷原子状态的探测,然而该成像方式受探测过程中光学平面干涉、激光功率、频率、空间位置抖动等方面的扰动,最终形成的冷原子图像总是会残余部分空间结构噪声,导致成像质量的下降。尤其是对于冷原子密度稀薄的区域或者飞行时间较久的情况,往往需要大量的重复和平均才能得到理想的信噪比,然而这样不仅导致时间周期大幅度增加,还会引入大量随机噪声。本文基于机器学习提出了一种单拍冷原子成像方案,在该方案中仅需对冷原子进行单次吸收成像,对应背景图片可以通过自动编码器的神经网络来进行生成,有效降低了成像的空间条纹噪声,大幅度提高成像质量,可以用于冷原子单循环多次成像。

Rydberg atoms possess highly excited valence electrons that are far away from atomic cations. Compared with ground states, Rydberg states are excited states with a high principal quantum number n that exhibit large electric dipole moments and have a variety of applications in quantum information processing. In this communication, we report the measurement of the ${}^6$Li Rydberg excitation spectrum by ladder-type electromagnetically induced transparency (EIT) in a vapor cell. The 2$p\to ns/nd$ EIT spectra were recorded by sweeping the frequency of an ultraviolet Rydberg pumping laser while keeping the probing laser resonant to the $2s\to 2p$ transition. All lasers were locked on an ultrastable optical Fabry-Pérot cavity and measured by an optical frequency comb. Our results provide valuable information to precisely determine quantum defects and enable novel experiments with Rydberg-dressed ultracold Fermi gases.