Figure 1: The Wigner quasiprobability distribution for a) the vacuum b) An n = 1 Fock state (e.g. a single photon) c) An n = 5 Fock state.
1. P(x, p)是实数
2. x 和p的概率分布由边缘决定:
如果系统是纯态,则
. 如果系统是纯态,则
通常密度矩阵ρ̂的秩为1
3. P(x, p)有以下的反射对称性:
时间对称性:
空间对称性:
4. P(x, p)是伽利莱协变:
不是劳伦兹协变性
5. 如果没有外力作用,在相位空间中每个点的运动方程符合经典力学:
事实上如果外力是谐波也满足
6. 状态重叠的计算公式:
7. 期望值运算子被认为是维格那变换的相空间平均:
8. 为了使P(x, p)代表物理(正)密度矩阵:
9. 利用柯西- Schwarz不等式,对于纯的状态,它被限制为有界,
维格纳演进方程
Figure 2: Wigner function for the simple harmonic oscillator ground state, displaced from the origin of phase space (i.e., a coherent state). (Click to animate.) Note the rigid rotation, identical to classical motion: this is a special feature of the SHO. From the general pedagogy web-site.[6]
Figure 7: A contour plot of the Wigner–Ville distribution for a chirped pulse of light. The plot makes it obvious that the frequency is a linear function of time.
^E.P. Wigner, "On the quantum correction for thermodynamic equilibrium", Phys. Rev.40 (June 1932) 749–759. doi:10.1103/PhysRev.40.749
^H. Weyl, Z. Phys.46, 1 (1927). doi:10.1007/BF02055756; H. Weyl, Gruppentheorie und Quantenmechanik (Leipzig: Hirzel) (1928); H. Weyl, The Theory of Groups and Quantum Mechanics (Dover, New York, 1931).
^H.J. Groenewold, "On the Principles of elementary quantum mechanics",Physica,12 (1946) 405–460. doi:10.1016/S0031-8914(46)80059-4
^J.E. Moyal, "Quantum mechanics as a statistical theory", Proceedings of the Cambridge Philosophical Society, 45, 99–124 (1949). doi:10.1017/S0305004100000487
^Specifically, since this convolution is invertible, in fact, no information has been sacrificed, and the full quantum entropy has not increased, yet. However, if this resulting Husimi distribution is then used as a plain measure in a phase-space integral evaluation of expectation values without the requisite star product of the Husimi representation, then, at that stage, quantum information has been forfeited and the distribution is a semi-classical one, effectively. That is, depending on its usage in evaluating expectation values, the very same distribution may serve as a quantum or a classical distribution function.
^葛哲学, and 陈仲生. "Matlab 时频分析技术及其应用." 人民邮电出版社, pp10-15 (2006).
延伸阅读
M. Levanda and V Fleurov, "Wigner quasi-distribution function for charged particles in classical electromagnetic fields", Annals of Physics, 292, 199–231 (2001). arXiv:cond-mat/0105137