Collective strong coupling of light and matter with cold atoms in a ring resonator

自激光发展以来，光腔在原子、分子和光学物理中起着核心作用。在这样的空腔中，增加的场强可以获得各种非线性光学现象，并且增加的相互作用长度可以检测甚至微量的气体。对于足够小的空腔中的大量原子，系统进入集体强耦合状态。在这种情况下，原子和腔场协同工作，产生了丰富的非线性动力学。最简单的谐振器设计包括一对平行反射镜，但包含三个或更多反射镜的环形几何结构在许多重要应用中使用。环形激光陀螺仪构成了导航系统中旋转传感的基础，无源环形谐振器已被用于测量手性液体中的光学活性。在这里，我们提出了在原子和光的集体强耦合状态下，在光学环腔中使用超冷气体的实验。该系统可应用于分子的激光冷却、自组织、量子模拟和精密计量。实验的第一阶段旨在了解空腔增强冷却作为一种推广激光冷却用于分子的方法。这一领域的初步研究表明，原子的空间自组织在增强腔模式相干散射中起着至关重要的作用。虽然关于这个主题的大部分理论工作都是在环形几何结构中进行的，但现有的少数空腔冷却实验已经利用了驻波谐振器。因此，我们将完美地研究提出的环几何的优点，涉及平移不变性和简并腔本征模式之间的相干动量交换。在实验的第二阶段，我们将进行凝聚态系统的直接量子模拟。利用光学晶格势中的量子气体来模拟各种固态晶体系统已经取得了惊人的成功。然而，在大多数工作中缺少的一个因素是任何原子对晶格势的逆作用。在典型的实验中，与固体和谐振器中的光学晶格不同，底层的光学晶格不受原子位置或运动的影响。最近在高精细腔中对玻色-爱因斯坦凝聚体的实验开始了对腔光力学的研究，并证明了向超固体的量子相变。我们将利用环几何来研究在原子密度改变光势的情况下具有移动晶格的系统。这将为晶格激发起重要作用的凝聚态物质系统提供一个关键的试验场。

Optical cavities have played a central role in atomic, molecular, and optical physics since the development of the laser. Within such cavities, increased field intensity gives access to a variety of nonlinear optical phenomena, and increased interaction length allows detection of even trace amounts of gases. For large numbers of atoms in small enough cavities, the system enters a regime of collective strong coupling. In this case the atoms and cavity field behave cooperatively, giving rise to a rich nonlinear dynamics.The simplest resonator design comprises a pair of parallel mirrors, but ring geometries involving three or more mirrors are used in a number of important applications. Ring laser gyroscopes form the basis of rotation sensing in navigation systems, and passive ring resonators have been used to measure optical activity in chiral liquids. Here we propose experiments with ultracold gases in an optical ring cavity, operating in the regime of collective strong coupling of atoms and light. This system has applications to laser cooling of molecules, self-organisation, quantum simulation, and precision metrology. The first phase of the experiment aims to understand cavity-enhanced cooling as a way to generalise laser cooling for use with molecules. Preliminary work in this field suggests that spatial self-organisation of atoms plays a crucial role in enhancing the coherent scattering into the cavity mode. Although the majority of theoretical work on this topic has been carried out within the ring geometry, the few existing cavity cooling experiments have utilised standing wave resonators. We will therefore be perfectly placed to investigate proposed advantages of the ring geometry, related to translational invariance and the coherent exchange of momentum between degenerate cavity eigenmodes.In the second phase of the experiment we will perform direct quantum simulation of condensed matter systems. There has been phenomenal success using quantum gases in optical lattice potentials to mimic a variety of solid-state crystalline systems. However one ingredient missing in most of this work is any atomic backaction onto the lattice potential. In typical experiments, the underlying optical lattice is unaffected by the position or motion of the atoms, in contrast with solids and with optical lattices in resonators. Recent experiments with Bose-Einstein condensates in high-finesse cavities have begun to study cavity optomechanics, and a quantum phase transition to a supersolid has been demonstrated. We will exploit the ring geometry to study systems with moving lattices in a regime where atom density modifies the optical potential. This will provide a key testing ground for condensed matter systems where lattice excitations play an important role.