Phase Space Correspondence between Classical Optics and Quantum Mechanics

Abstract

The paper scrutinizes both the similarities and the differences between the classical optics and quantum mechanical theories in phase space, especially between the Wigner distribution functions defined in the respective phase spaces. Classical optics is able to provide an understanding of either the corpuscular or wave aspects of quantum mechanics, reflected in phase space through the classical limit of the quantum Wigner distribution function or the Wigner distribution function in classical optics, respectively. However, classical optics, as any classical theory, cannot mimic the wave-particle duality that is at the heart of quantum mechanics. Moreover, it is never enough underlined that, although the mathematical phase space formalisms in classical optics and quantum mechanics are very similar, the main difference between these theories, evidenced in the results of measurements, is as deep as it can get even in phase space. On the other hand, the phase space treatment allows an unexpected similar treatment of interference phenomena, although quantum and classical superpositions of wavefunctions and fields, respectively, have a completely different behavior. This similarity originates in the bilinear character of the Wigner distribution function in both quantum mechanics and classical optical wave theory. Actually, the phase space treatment of the quantum and classical wave theory is identical from the mathematical point of view, if the Planck constant is replaced by the wavelength of light. Even Wigner distribution functions of particular quantum states, such as the Schrodinger cat state, can be mimicked by classical optical means, but not the true quantum character, which resides in the probability significance of the wavefunction, in comparison to the physical realness of classical wave fields.