Theoretische Physik, Universität des Saarlandes, D-66123 Saarbrücken, Germany.
JILA, National Institute of Standards and Technology and Department of Physics, University of Colorado, Boulder, Colorado 80309-0440, USA.
Phys Rev Lett. 2019 Aug 2;123(5):053601. doi: 10.1103/PhysRevLett.123.053601.
We theoretically analyze superradiant emission of light from an ultracold gas of bosonic atoms confined in a bad cavity. A metastable dipolar transition of the atoms couples to the cavity field and is incoherently pumped, and the mechanical effects of cavity-atom interactions tend to order the atoms in the periodic cavity potential. By means of a mean-field model we determine the conditions on the cavity parameters and pump rate that lead to the buildup of a stable macroscopic dipole emitting coherent light. We show that this occurs when the superradiant decay rate and the pump rate exceed threshold values of the order of the photon recoil energy. Above these thresholds superradiant emission is accompanied by the formation of stable matter-wave gratings that diffract the emitted photons. Outside of this regime, instead, the optomechanical coupling can give rise to dephasing or chaos, for which the emitted light is respectively incoherent or chaotic. These behaviors exhibit the features of a dynamical phase transitions and emerge from the interplay between global optomechanical interactions, quantum fluctuations, and noise.
我们从理论上分析了玻色原子超冷气体在不良腔中的超辐射光发射。原子的亚稳态偶极跃迁与腔场耦合并非相干泵浦，而腔-原子相互作用的力学效应倾向于在周期性腔势中对原子进行排序。通过平均场模型，我们确定了腔参数和泵浦率的条件，这些条件导致稳定的宏观偶极子发射相干光。我们表明，当超辐射衰减率和泵浦率超过光子反冲能量的量级的阈值时，就会发生这种情况。在这些阈值之上，超辐射发射伴随着稳定的物质波光栅的形成，这些光栅会使发射的光子发生衍射。在这个范围之外，相反，光机械耦合会导致退相或混沌，由此发射的光分别是非相干或混沌的。这些行为表现出动力学相变的特征，并且源自全局光机械相互作用、量子涨落和噪声的相互作用。
