The Effect of Measurement on Interference in Phase-Space

Vasiliy Makhalov, Andrey Turlapov

For a long periodic chain of Bose condensates prepared in the free space, the subsequent evolution and interference dramatically depend on the difference between the phases of the adjacent and more distant condensates. If the phases are equal, the initial periodic density distribution reappears at later times, which is known as the Talbot effect. For randomly-related phases, we have found that a spatial order also appears in the interference, while the evolution of the fringes differs with the Talbot effect qualitatively. Even a small phase disorder is sufficient for qualitatively altering the interference, though maybe at long evolution times. This effect may be used for measuring the amount of coherence between adjacent condensates and the correlation length along the chain.

Wolfgang P. Schleich, JOHN ARCHIBALD WHEELER

James E Beecham

In the Aharonov–Bohm (AB) effect, electrons form an interference pattern whose bright and dark fringes shift position when the magnetic flux confined within a nearby solenoid is changed, even though the electrons travel only through regions where the magnetic field is zero. Operationally, the experiment compares electron interference patterns obtained under different solenoid current (or enclosed flux) conditions, revealing a measurable phase difference—observed as fringe displacement—between the two electron paths despite the absence of any force acting on the electrons along those paths. Each electron arrives as a dot, but many dots build up the interference pattern. The effect tracks the enclosed flux (current level), with on/off as an illustrative extreme. What is measured is phase difference / fringe displacement, i.e., a relative effect between the two paths. This Aharonov-Bohm effect is famous in modern physics and widely regarded as proof that electromagnetic potentials possess physical reality even in regions where fields vanish. This paper reinterprets the AB effect by reframing it using the SP3 (space-phase) theory.

Gerard J Milburn, Daniel F. Walls

We will determine the effect of dissipation and nonunit quantum efficiency on the oscillations in the photon-number distribution for squeezed states. These oscillations are evidence of interference in phase space and thus our results show the effect of dissipation on such interference effects. Our method, based on the Q function, enables a direct comparison of the quantum and classical phase-space descriptions.

Tilman Pfau