Classical interference is a quantum effect

L. Mandeļ

Although interference of light is commonly regarded as a classical wave phenomenon, interesting fourth‐order interference effects are exhibited by correlated photon pairs, which violate classical probability. The effects manifest themselves in that the visibility is larger than allowed by classical theory, or the interference is independent of the light intensity, in violation of classical theory. In some situations classical optics predicts no interference at all, whereas quantum optics does. The interference technique has been used to measure time intervals between two photons with fsec resolution. Several examples of experiments in which non‐classical interference effects were observed will be described.

J. Anandan

C. S. Unnikrishnan

I present conclusive arguments to show that a recent claim of observation of quantum-like effects of the magnetic vector potential in the classical macrodomain is spurious. The `one dimensional interference patterns' referred to in the paper by R. K. Varma et al (Phys. Lett. A 303 (2002) 114-120) are not due to any quantum-like wave phenomena. The data reported in the paper are not consistent with the interpretation of interference, or with the topology of the Aharonov-Bohm effect. The assertion that they are evidence of A-B like effect in the classical macrodomain is based on inadequate appreciation of basic physical facts regarding classical motion of electrons in magnetic fields, interference phenomena, and the A-B effect.

Chris Philippidis, Christopher Dewdney, Basil J. Hiley

Timothy H. Boyer

Classical electromagnetic lag effects can give rise to quantum interference pattern shifts such as that observed experimentally in the Aharonov-Bohm effect involving electrons passing a solenoid. This paper presents an extensive comparison between interference pattern shifts based upon classical electromagnetic fields, and based upon classical electromagnetic potentials as suggested by Aharonov and Bohm. Stress is placed upon the difference between two types of interference pattern shifts: those involving deflection of the entire interference pattern and those involving a deflection of only the double-slit pattern while leaving the single-slit envelope undisplaced. The first type of shift is produced by a classical deflecting force. The second type of shift can be produced by classical electromagnetic lag effects, and is also the type of shift associated with the Aharonov-Bohm effect. The two types are confused in the literature. A new experiment is proposed which shows the relationship between a classical lag effect, due to electrostatic fields on electrons passing along different paths, and the associated quantum interference pattern shifts. The experiment is analyzed in detail using the WKB approximation in the Schr\"odinger equation and also semiclassical ideas. The classical limit for the situation illustrates the Bohr correspondence principle, showing the relative lag between the electron wave packets becoming a measurable classical lag with a disappearance of the interference pattern as the lag becomes large compared to the wave-packet dimensions. For small shifts, the phase change predicted for the new experiment is identical with the scalar potential effect proposed by Aharonov and Bohm for a slightly different, time-varying experimental arrangement. The theoretical and experimental differences for large phase shifts are noted. The possibility is raised that a new classical electromagnetic lag effect may occur for electrons passing a small solenoid. Using a particular model for energy conservation, the predicted lag effect can be calculated and is associated with a quantum interference pattern shift of the same magnitude as predicted by Aharonov and Bohm based upon the electromagnetic vector potential. Thus the possibility exists that the experiments of Chambers and of M\"ollenstedt and Bayh may not confirm the ideas of Aharonov and Bohm on the vector potential in quantum theory. Several experiments are suggested which allow confirmation that the Aharonov-Bohm effect indeed involves local effects of the classical electromagnetic potential, rather than local electromagnetic fields leading to a new classical lag effect and hence to the observed quantum interference pattern shift.