发表机构
Institut für Angewandte Physik, Universität Bonn; Kirchhoff-Institut für Physik, Universität Heidelberg（波恩大学应用物理研究所; 海德堡大学基尔霍夫物理研究所）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究建立耦合到物质电子激发库的光子自由能模型，分析正则与巨正则系综下光子玻色-爱因斯坦凝聚体的涨落，还提出盒形势中光子气体模型，预测了长程相干的瞬态微凝聚体类岛状涨落模式。
AI 中文摘要
光子是几乎无相互作用的粒子，因此热化的光子集合通常并非来自直接的粒子-粒子相互作用，而是通过与物质接触获得，该物质可构成光子气体的库。我们为填充了物质（例如液体染料）的光学微腔中的光子建立理论模型，目的是利用耦合到物质电子激发库的无相互作用光子的自由能描述来研究涨落性质。首先，我们对凝聚体采用单模描述。当物质库的相对尺寸较小时（对应正则系综区域），凝聚体粒子数涨落很小，推导得到的自由能势呈现常见的墨西哥帽形状，从而发生自发对称性破缺。相反，当库的相对尺寸较大时（对应巨正则系综区域），涨落与平均粒子数一样大。我们表明，由此得到的自由能势呈现碗状形式，在原点处有单个极小值，因此预计会出现不存在自发对称性破缺的基态宏观占据（即玻色-爱因斯坦凝聚）。我们还提供了一个模型，用于处理被困在盒形势中且与库具有空间分布耦合的光子气体，该模型例如预测了具有长程相干性的岛状统计涨落模式，类似于瞬态微凝聚体。
英文摘要
Photons are mutually nearly noninteracting particles, so thermalized photon ensembles are commonly obtained not from direct particle-particle-interactions but rather from contact with matter, which can constitute a reservoir for the photon gas. We develop a theory model for photons in a material-filled (e.g. liquid dye) optical microcavity, with the aim to study the fluctuation properties using a free-energy description for noninteracting photons coupled to a reservoir of material electronic excitations. To begin with, we use a single mode description for the condensate. For a small relative size of the material reservoir, corresponding to the canonical regime, condensate number fluctuations are small, and the derived free energy landscape takes the usual Mexican-hat shaped form such that spontaneous symmetry breaking occurs. In contrast, for a large relative size of the reservoir, corresponding to the grand canonical regime, fluctuations become as large as the average particle number. We show that the resulting free energy landscape acquires a bowl-shaped form, with a single minimum at the origin. Thus, a macroscopic occupation of the ground state (i.e., Bose-Einstein condensation) in the absence of spontaneous symmetry breaking is expected. We also provide a model for the treatment of a photon gas trapped in a box-shaped potential with spatially distributed coupling to a reservoir. The model predicts, for example, a statistically fluctuating pattern of islands with long-range coherence, resembling transient microcondensates.
Comments19 pages, 4 figures
