虚拟全光活塞驱动下光子流体的相变
Phase transitions of photon fluid flows driven by a virtual all-optical piston
摘要：
活塞问题，即静止的均匀气体在运动活塞作用下的动力学问题，是物理学的基本问题，也是冲击波物理学中的一个典型问题。我们从理论上和实验上研究了光子流体的类似问题，结果证明这是强烈影响的色散特性的问题。该实验利用了一个纤维光学设置，其中输入光的频率的全光学控制的准瞬时变化模仿活塞动作。我们发现，流动表现出相变，涉及交叉的制度，其特征在于由2-冲击（推动活塞）2-稀疏波（缩回活塞），与空化状态的出现在临界振幅的跳跃。重要的是，真空点进入2-激波的出现标志着向光子流体所特有的状态的过渡。我们的观察允许广泛的和定量的测试状态的最先进的描述的色散黎曼问题，即惠瑟姆调制理论，适用于通用散焦非线性薛定谔方程。
英文摘要：
The piston problem, i.e. the dynamics in a uniform gas at rest under the action of a moving piston is fundamental problem of physics and a canonical case study in shock wave physics. We investigate theoretically and experimentally the analogous problem for a photon fluid, which turns out to be strongly influenced by the dispersive character of the problem. The experiment makes use of a fiber optics setup where an all-optically controlled quasi instantaneous change of frequency of the input light mimics the piston action. We show that the flow exhibits phase transitions which involve cross-over from regimes characterized by 2-shocks (pushing piston) to 2-rarefaction waves (retracting piston), with the appearance of cavitating states at critical amplitudes of the jump. Importantly, the appearance of vacuum points into the 2-shock marks the transition to a regime which is unique to the photon fluid. Our observations allow for the extensive and quantitative test of the state of the art description of the dispersive Riemann problem, i.e. Whitham modulation theory, applied to the universal defocusing nonlinear Schrödinger equation.
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