We predict a new mechanism to induce collective excitations and a nonequilibrium phase transition of fermionic superfluids via a sudden switch on of two-body loss, for which we extend the BCS theory to fully incorporate a change in particle number. We find that a sudden switch on of dissipation induces an amplitude oscillation of the superfluid order parameter accompanied by a chirped phase rotation as a consequence of particle loss. We demonstrate that when dissipation is introduced to one of the two superfluids coupled via a Josephson junction, it gives rise to a nonequilibrium dynamical phase transition characterized by the vanishing dc Josephson current. The dissipation-induced collective modes and nonequilibrium phase transition can be realized with ultracold fermionic atoms subject to inelastic collisions.

中文翻译：

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耗散费米子超流体中的集体激发和非平衡相变

我们预测了一种通过双体损失的突然开启来诱导集体激发和费米子超流体的非平衡相变的新机制，为此我们扩展了 BCS 理论以完全纳入粒子数的变化。我们发现耗散的突然开启会引起超流体阶参数的振幅振荡，并伴随着由于粒子损失而导致的啁啾相位旋转。我们证明，当耗散被引入通过约瑟夫森结耦合的两个超流体之一时，它会引起非平衡动态相变，其特征在于消失的直流约瑟夫森电流。耗散诱导的集体模式和非平衡相变可以通过经受非弹性碰撞的超冷费米子原子来实现。