Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA.
Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544, USA and Institute of Quantum Electronics, ETH Zurich, 8093 Zurich, Switzerland.
Phys Rev Lett. 2013 Nov 27;111(22):220408. doi: 10.1103/PhysRevLett.111.220408.
We investigate the near-critical dynamics of atomic density fluctuations in the nonequilibrium self-organization transition of an optically driven quantum gas coupled to a single mode of a cavity. In this system cavity-mediated long-range interactions between atoms, tunable by the drive strength, lead to softening of an excitation mode recently observed in experiments. This phenomenon has previously been studied within a two-mode approximation for the collective motional degrees of freedom of the atomic condensate, which results in an effective open-system Dicke model. Here, including the full spectrum of atomic modes we find a finite lifetime for a rotonlike mode in the Bogoliubov excitation spectrum that is strongly pump dependent. The corresponding decay rate and critical exponents for the phase transition are calculated explaining the nonmonotonic pump-dependent atomic damping rate observed in recent experiments. We compute the near-critical behavior of the intracavity field fluctuations that has been previously shown to be enhanced with respect to the equilibrium Dicke model in a two-mode approximation. We highlight the role of the finite size of the system in the suppression of it below the expectations of the open Dicke model.
我们研究了在光驱动量子气体与腔的单一模式耦合的非平衡自组织转变中原子密度涨落的近临界动力学。在这个系统中，通过驱动强度可调的腔介导的原子之间的长程相互作用，导致了最近在实验中观察到的激发模式软化。这种现象以前已经在集体运动自由度的双模近似中进行了研究原子凝聚物，导致有效开系统 Dicke 模型。在这里，我们包括原子模式的全谱，发现 Bogoliubov 激发谱中的类转子模式的有限寿命强烈依赖于泵浦。计算了相变的相应衰减率和临界指数，解释了最近实验中观察到的非单调泵依赖原子阻尼率。我们计算了腔内场涨落的近临界行为，在双模近似中，与平衡 Dicke 模型相比，该行为被证明得到了增强。我们强调了系统有限大小在抑制它低于开放 Dicke 模型的预期方面的作用。
