Department of Physics and State Key Laboratory of Low-Dimensional Quantum Physics, Tsinghua University, Beijing 100084, China.
Centre for Quantum and Optical Science, Swinburne University of Technology, Melbourne 3122, Australia.
Phys Rev Lett. 2018 Jan 26;120(4):045302. doi: 10.1103/PhysRevLett.120.045302.
We propose that the long-sought Fulde-Ferrell superfluidity with nonzero momentum pairing can be realized in ultracold two-component Fermi gases of ^{40}K or ^{6}Li atoms by optically tuning their magnetic Feshbach resonances via the creation of a closed-channel dark state with a Doppler-shifted Stark effect. In this scheme, two counterpropagating optical fields are applied to couple two molecular states in the closed channel to an excited molecular state, leading to a significant violation of Galilean invariance in the dark-state regime and hence to the possibility of Fulde-Ferrell superfluidity. We develop a field theoretical formulation for both two-body and many-body problems and predict that the Fulde-Ferrell state has remarkable properties, such as anisotropic single-particle dispersion relation, suppressed superfluid density at zero temperature, anisotropic sound velocity, and rotonic collective mode. The latter two features can be experimentally probed using Bragg spectroscopy, providing a smoking-gun proof of Fulde-Ferrell superfluidity.
我们提出，通过创建具有多普勒频移斯塔克效应的闭壳态暗态，用光来调谐 ^{40}K 或 ^{6}Li 原子的超冷双组分费米气体的磁费什巴赫共振，可实现具有非零动量配对的长期寻求的富勒-费雷尔超流性。在该方案中，施加两个反向传播的光场以将闭壳通道中的两个分子态耦合到激发的分子态，从而在暗态区域中严重违反伽利略不变性，从而有可能实现富勒-费雷尔超流性。我们针对两体和多体问题发展了场论公式，并预测富勒-费雷尔态具有显著的性质，例如各向异性单粒子色散关系，零温下抑制的超流密度，各向异性声速和类轮动集体模式。后两个特征可以使用布拉格光谱学进行实验探测，为富勒-费雷尔超流性提供确凿的证据。
