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词汇 Coherent states
分类 英语词汇 英语翻译词典
释义

Coherent states

中文百科

相干态

图1：使用零差检波测量的Nd:YAG激光器发射的电场的三种不同的相干态与相之间的函数关系，电场中量子噪音的数量与相完全不相关。量子噪音不随场强度的增高（振幅）而增强，因此变得越来越不足道。在强度非常高的情况下振荡就好像是完全没有噪音的经典波一样。从上向下平均光子数位4.2、25.2和924.5
图2：图1中第二相干态的振荡波包。不论电场的相是多少其分布是宽度不变的高斯分布
图3：图2的相干态的维格纳分布分布的中心是相干态的振幅，而且是从这一点出发完全对称的。图中的波动是由试验误差导致的
图4：测量到-n-光子的可能性，图3相干态的光子数分布。由于泊松分布的需要平均分子数等于分子数分布的方差。方块表示理论值，圆点是试验数据

相干态是量子力学中量子谐振子能够达到的一种特殊的量子状态。量子谐振子的动力学性能和经典力学中的谐振子很相似。1926年埃尔温·薛定谔在解满足对应原理的薛定谔方程时找到的第一个量子力学解就是相干态。在大量物理系统中量子谐振子和相干态存在。比如一个位于二次方位能井中的粒子的振荡运动就是一个相干态。1963年罗伊·格劳伯把相干态引入量子电动力学和玻色子量子场论。

英语百科

Coherent states 相干态

Figure 1: The electric field, measured by optical homodyne detection, as a function of phase for three coherent states emitted by a Nd:YAG laser. The amount of quantum noise in the electric field is completely independent of the phase. As the field strength, i.e. the oscillation amplitude α of the coherent state is increased, the quantum noise or uncertainty is constant at 1/2, and so becomes less and less significant. In the limit of large field the state becomes a good approximation of a noiseless stable classical wave. The average photon numbers of the three states from bottom to top are <n>=4.2, 25.2, 924.5[5]
Figure 2: The oscillating wave packet corresponding to the second coherent state depicted in Figure 1. At each phase of the light field, the distribution is a Gaussian of constant width.
Figure 3: Wigner function of the coherent state depicted in Figure 2. The distribution is centered on state's amplitude α and is symmetric around this point. The ripples are due to experimental errors.
Figure 4: The probability of detecting n photons, the photon number distribution, of the coherent state in Figure 3. As is necessary for a Poissonian distribution the mean photon number is equal to the variance of the photon number distribution. Bars refer to theory, dots to experimental values.

In physics, specifically in quantum mechanics, a coherent state is the specific quantum state of the quantum harmonic oscillator, often described as a state which has dynamics most closely resembling the oscillatory behavior of a classical harmonic oscillator. It was the first example of quantum dynamics when Erwin Schrödinger derived it in 1926, while searching for solutions of the Schrödinger equation that satisfy the correspondence principle. The quantum harmonic oscillator and hence, the coherent states, arise in the quantum theory of a wide range of physical systems. For instance, a coherent state describes the oscillating motion of a particle confined in a quadratic potential well (for an early reference, see e.g. Schiff's textbook).
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