Department of Applied Physics, Stanford University, MC 305, Stanford, California 94305, USA.
E.L. Ginzton Laboratory, Stanford University, MC 305, Stanford, California 94305-4088, USA.
Nat Commun. 2017 Feb 17;8:14386. doi: 10.1038/ncomms14386.
Phase transitions, where observable properties of a many-body system change discontinuously, can occur in both open and closed systems. By placing cold atoms in optical cavities and inducing strong coupling between light and excitations of the atoms, one can experimentally study phase transitions of open quantum systems. Here we observe and study a non-equilibrium phase transition, the condensation of supermode-density-wave polaritons. These polaritons are formed from a superposition of cavity photon eigenmodes (a supermode), coupled to atomic density waves of a quantum gas. As the cavity supports multiple photon spatial modes and because the light-matter coupling can be comparable to the energy splitting of these modes, the composition of the supermode polariton is changed by the light-matter coupling on condensation. By demonstrating the ability to observe and understand density-wave-polariton condensation in the few-mode-degenerate cavity regime, our results show the potential to study similar questions in fully multimode cavities.
相变是指多体系统的可观察性质发生不连续变化，可以在开放系统和封闭系统中发生。通过将冷原子置于光学腔中，并诱导光与原子激发之间的强耦合，可以在实验中研究开放量子系统的相变。在这里，我们观察和研究了一种非平衡相变，即超模密度波极化激元的凝聚。这些极化激元是由腔光子本征模式（超模）的叠加形成的，与量子气体的原子密度波耦合。由于腔支持多个光子空间模式，并且由于光物质耦合可以与这些模式的能量分裂相媲美，因此在凝聚时，光物质耦合会改变超模极化激元的组成。通过证明在少数模式简并腔条件下观察和理解密度波极化激元凝聚的能力，我们的结果表明在完全多模腔中研究类似问题的潜力。
