Institute for Quantum Electronics, ETH Zürich, 8093 Zürich, Switzerland.
Nature. 2010 Apr 29;464(7293):1301-6. doi: 10.1038/nature09009.
A phase transition describes the sudden change of state of a physical system, such as melting or freezing. Quantum gases provide the opportunity to establish a direct link between experiments and generic models that capture the underlying physics. The Dicke model describes a collective matter-light interaction and has been predicted to show an intriguing quantum phase transition. Here we realize the Dicke quantum phase transition in an open system formed by a Bose-Einstein condensate coupled to an optical cavity, and observe the emergence of a self-organized supersolid phase. The phase transition is driven by infinitely long-range interactions between the condensed atoms, induced by two-photon processes involving the cavity mode and a pump field. We show that the phase transition is described by the Dicke Hamiltonian, including counter-rotating coupling terms, and that the supersolid phase is associated with a spontaneously broken spatial symmetry. The boundary of the phase transition is mapped out in quantitative agreement with the Dicke model. Our results should facilitate studies of quantum gases with long-range interactions and provide access to novel quantum phases.
相变描述了物理系统状态的突然变化，例如熔化或凝固。量子气体提供了在实验和捕捉基本物理的通用模型之间建立直接联系的机会。Dicke 模型描述了集体物质-光相互作用，并已被预测会显示出有趣的量子相变。在这里，我们在由玻色-爱因斯坦凝聚体与光学腔耦合形成的开放系统中实现了 Dicke 量子相变，并观察到自组织超固态相的出现。相变是由凝聚原子之间的无限长程相互作用驱动的，这种相互作用是由涉及腔模和泵浦场的双光子过程引起的。我们表明，相变由 Dicke 哈密顿量描述，包括反向旋转耦合项，并且超固态相与空间对称性的自发破缺有关。相变的边界与 Dicke 模型定量一致。我们的结果应该有助于研究具有长程相互作用的量子气体，并提供进入新的量子相的途径。
