Investigation of Nonclassical and Nonlocal Effects in Fourth-Order Optical Interference

Jan Peřina, Z. Hradil, Branislav Jurčo

L. Mandeļ

Although we tend to think of optical interference as a classical wave phenomenon, recent experiments have revealed a number of effects that are not describable in classical terms. This is particularly true of interference effects involving the detection of a photon pair. We shall refer to them as fourth order interference, on the grounds that the joint probability density for the detection of one photon at r sub 1 at time t and another r sub 2 at time t is proportional to the fourth order correlation function of the field. This probability is readily measured when two photodetectors are positioned at r sub 1 and r sub 2 and the signals from the two detectors are fed to a coincidence counter that registers 'simultaneous' detections by the two detectors in coincidence. The topics covered include: fourth order interference measurements; the Franson experiment; and experimental test of the de Broglie guided wave theory.

Jeffrey H. Shapiro, Ke-Xun Sun

A theoretical construct is presented for fourth-order interference between the signal and the idler beams of a parametric downconverter. Previous quantum treatments of fourth-order interference have employed correlated single-photon wave packets. The introduced approach, however, relies on Gaussian-state field correlations, which were previously used to characterize quadrature-noise squeezing produced by an optical parametric amplifier and nonclassical twin-beam generation in an optical parametric oscillator. Three principal benefits accrue from the correlation-function formalism. First, the quantum theory of fourth-order interference is unified with that for the other nonclassical effects of χ(2) interactions, i.e., squeezing and twin-beam production. Second, the semiclassical photodetection limit on Gaussian-state fourth-order interference is established; a purely quantum effect can be claimed at fringe visibilities substantially below the 50% level. Finally, both photon-coincidence counting (within the low-photon-flux regime) and intensity interferometry (in the high-photon-flux limit) are easily analyzed within a common framework.

Holger Schmidt

John G. Rarity, P. R. Tapster

We present an experimental demonstration of a fourth-order interference effect first suggested by Franson [Phys. Rev. Lett. 62, 2205 (1989)], where pair photons are directed to two separated Mach-Zehnder interferometers. Apparent nonlocal control of the output ports in which coincident photons are detected can be demonstrated. We show that this effect is present when one of the photons has passed through 170 m of multimode optical fiber. Such a system could form the basis of an interception-proof communication system.

R. Loudon