论文标题
自由空间中的非平衡超级级相变
A non-equilibrium superradiant phase transition in free space
论文作者
论文摘要
存在一类系统，其中耗散，外部驱动器和互动竞争并引起没有驱动器将不存在的非平衡阶段。在那里，与在平衡时相比的兰道相反，可以在没有任何对称性的情况下进行相变。最简单的驱动耗散量子系统之一是由两级原子组成的，该原子包含在小于原子过渡立方的波长的体积中，由光场驱动。原子与驾驶场的集体耦合与它们的合作衰减之间的竞争应导致在所有原子偶极子均被浮游生物和由超级自发发射控制的阶段之间的过渡。在这里，我们使用自由空间中的激光冷却原子的铅笔形云实现了这种模型，沿其主轴光学兴奋，并观察到预测的相位。鉴于获得自由空间超级激光器或观察新类型的时间晶体，我们的演示很有希望。
A class of systems exists in which dissipation, external drive and interactions compete and give rise to non equilibrium phases that would not exist without the drive. There, phase transitions could occur without the breaking of any symmetry, yet with a local order parameter, in contrast with the Landau theory of phase transitions at equilibrium. One of the simplest driven dissipative quantum systems consists of two-level atoms enclosed in a volume smaller than the wavelength of the atomic transition cubed, driven by a light field. The competition between collective coupling of the atoms to the driving field and their cooperative decay should lead to a transition between a phase where all the atomic dipoles are phaselocked and a phase governed by superradiant spontaneous emission. Here, we realize this model using a pencil-shaped cloud of laser cooled atoms in free space, optically excited along its main axis, and observe the predicted phases. Our demonstration is promising in view of obtaining free-space superradiant lasers or to observe new types of time crystals.
