Department of Physics, The University of Texas at Dallas, Richardson, Texas 75080-3021, USA.
Phys Rev Lett. 2018 Jun 29;120(26):263202. doi: 10.1103/PhysRevLett.120.263202.
Floquet dynamics of a quantum system subject to periodic modulations of system parameters provides a powerful tool for engineering new quantum matter with exotic properties. While system dynamics is significantly altered, the periodic modulation itself is usually induced externally and independent of Floquet dynamics. Here we propose a new type of Floquet physics for a Bose-Einstein condensate (BEC) subject to a shaken lattice generated inside a cavity, where the shaken lattice and atomic Floquet bands are mutually dependent, resulting in self-adapted Floquet dynamics. In particular, the shaken lattice induces Floquet quasienergy bands for the BEC, whose backaction leads to a self-adapted dynamical normal-superradiant phase transition for the shaken lattice. Such self-adapted Floquet dynamics shows two surprising and unique features: (i) The normal-superradiant phase transition possesses a hysteresis even without atom interactions. (ii) The dynamical atom-cavity steady state could exist at free energy maxima. The atom interactions strongly affect the phase transition of the BEC from zero to finite momenta. Our results provide a powerful platform for exploring self-adapted Floquet physics, which may open an avenue for engineering novel quantum materials.
受系统参数周期性调制的量子系统的 Floquet 动力学为具有奇异性质的新型量子物质的工程提供了强大的工具。虽然系统动力学发生了重大变化，但周期性调制通常是外部诱导的，并且与 Floquet 动力学无关。在这里，我们提出了一种新型的 Floquet 物理，用于在腔内产生的晶格中受晶格晃动的玻色-爱因斯坦凝聚体（BEC），其中晶格晃动和原子 Floquet 带相互依赖，导致自适应 Floquet 动力学。具体来说，晶格晃动会为 BEC 诱导 Floquet 准能带，其反作用会导致晶格晃动的自适应动态正常超辐射相变。这种自适应的 Floquet 动力学具有两个令人惊讶和独特的特点：（i）即使没有原子相互作用，正常超辐射相变也具有滞后性。（ii）动力学原子腔稳态可能存在于自由能最大值处。原子相互作用强烈影响 BEC 从零到有限动量的相变。我们的结果为探索自适应 Floquet 物理提供了一个强大的平台，这可能为新型量子材料的工程开辟了一条途径。
