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

自激光器问世以来，光学谐振腔在原子、分子和光学物理中一直扮演着重要的角色。在这样的空腔内，增加的场强可以获得各种非线性光学现象，增加的相互作用长度可以检测甚至痕量的气体。对于足够小的腔中的大量原子，系统进入集体强耦合状态。最简单的谐振腔设计包括一对平行的反射镜，但是在许多重要的应用中使用包括三个或更多反射镜的环形几何结构。环形激光陀螺仪形成导航系统中旋转感测的基础，并且无源环形谐振器已被用于测量手性液体中的旋光性。在这里，我们提出的实验与超冷气体在光学环形腔，在原子和光的集体强耦合制度。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腔增强冷却作为一种将激光冷却推广用于分子的方法。在这一领域的初步工作表明，原子的空间自组织在增强相干散射到腔模中起着至关重要的作用。虽然大多数关于这个主题的理论工作都是在环形几何结构中进行的，但现有的几个腔体冷却实验都利用了驻波谐振器。因此，我们将完全处于调查拟议的优势，环几何，有关平移不变性和相干交换之间的动量简并腔eigenmodes.In实验的第二阶段，我们将进行直接量子模拟凝聚态系统。在光学晶格势中使用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成分是任何原子对晶格势的反作用。在典型的实验中，底层的光学晶格不受原子的位置或运动的影响，与固体和谐振器中的光学晶格相反。最近在高精细度腔中的玻色-爱因斯坦凝聚实验已经开始研究腔光学力学，并且已经证明了超固体的量子相变。我们将利用环几何来研究原子密度改变光学势的运动晶格系统。这将为晶格激发发挥重要作用的凝聚态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.