Bose-Einstein condensation of photons in an optical microcavity
Bose-Einstein condensation of photons in an optical microcavity
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DOI：
10.1038/nature09567
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发表时间：
2010-11-25
期刊：
影响因子：
64.8
通讯作者：
Weitz, Martin
中科院分区：
文献类型：
--
作者：
Klaers, Jan;Schmitt, Julian;Weitz, Martin
玻色-爱因斯坦凝聚（BEC）--在低温和高密度下具有整数自旋的粒子（玻色子）的宏观基态积累--已经在几个物理系统中观察到（1-9），包括冷原子气体和固态准粒子。然而，最无所不在的玻色气体，黑体辐射（与腔壁热平衡的辐射）没有显示这种相变。在这样的系统中，光子具有消失的化学势，这意味着当光子气体的温度变化时，它们的数量不守恒（10）;在低温下，光子在腔壁中消失，而不是占据腔基态。理论工作已经考虑了保持光子数的热化过程（BEC的先决条件），包括与热电子气体的康普顿散射（11）或非线性谐振器配置中的光子-光子散射（12，13）。在填充染料的光学微腔中，实验观察到二维光子气体的数量守恒热化（14），该微腔充当“白壁”盒。在这里，我们报告的玻色-爱因斯坦凝聚的光子在这个系统中的观察。腔镜提供了一个限制势和一个非零的有效光子质量，使得系统在形式上等价于一个被囚禁的大质量玻色子的二维气体。通过与染料分子的多次散射，光子热化至染料溶液的温度（室温）。在增加光子密度时，我们观察到以下BEC签名：光子能量具有玻色-爱因斯坦分布，在宽热翼顶部具有大量填充的基态模式;相变发生在预期的光子密度处，并表现出预测的对腔几何形状的依赖性;即使对于空间位移的泵浦点，基态模式也会出现。观察到的效应的前景包括研究极弱相互作用的低维玻色气体（9）和新的相干紫外源（15）。
Bose-Einstein condensation (BEC)-the macroscopic ground-state accumulation of particles with integer spin (bosons) at low temperature and high density-has been observed in several physical systems(1-9), including cold atomic gases and solid-state quasiparticles. However, the most omnipresent Bose gas, blackbody radiation (radiation in thermal equilibrium with the cavity walls) does not show this phase transition. In such systems photons have a vanishing chemical potential, meaning that their number is not conserved when the temperature of the photon gas is varied(10); at low temperatures, photons disappear in the cavity walls instead of occupying the cavity ground state. Theoretical works have considered thermalization processes that conserve photon number (a prerequisite for BEC), involving Compton scattering with a gas of thermal electrons(11) or photon-photon scattering in a nonlinear resonator configuration(12,13). Number-conserving thermalization was experimentally observed(14) for a two-dimensional photon gas in a dye-filled optical microcavity, which acts as a 'white-wall' box. Here we report the observation of a Bose-Einstein condensate of photons in this system. The cavity mirrors provide both a confining potential and a nonvanishing effective photon mass, making the system formally equivalent to a two-dimensional gas of trapped, massive bosons. The photons thermalize to the temperature of the dye solution (room temperature) by multiple scattering with the dye molecules. Upon increasing the photon density, we observe the following BEC signatures: the photon energies have a Bose-Einstein distribution with a massively populated ground-state mode on top of a broad thermal wing; the phase transition occurs at the expected photon density and exhibits the predicted dependence on cavity geometry; and the ground-state mode emerges even for a spatially displaced pump spot. The prospects of the observed effects include studies of extremely weakly interacting low-dimensional Bose gases(9) and new coherent ultraviolet sources(15).