The Physics of Ghost Imaging

TL;DR

Ghost imaging is a quantum phenomenon involving nonlocal interference, with two types demonstrated: one using entangled photons and the other using chaotic light, revealing fundamentally different physics.

Contribution

This paper clarifies the nonlocal two-photon interference physics underlying ghost imaging, distinguishing it from classical effects like ghost shadows.

Findings

Type-one ghost imaging relies on entangled photon pairs.

Type-two ghost imaging involves interference of two-photon amplitudes from chaotic light.

Ghost shadow phenomena are classical, unlike true ghost imaging.

Abstract

One of the most surprising consequences of quantum mechanics is the nonlocal multi-particle interference observable in joint-detection of distant particle-detectors. Ghost imaging is one of such phenomena. Two types of ghost imaging have been experimentally demonstrated since 1995. Type-one ghost imaging uses entangled photon pairs as the light source. The nonlocal point-to-point image-forming correlation is the result of a constructive-destructive superposition among a large number of biphoton amplitudes, a nonclassical entity corresponding to different yet indistinguishable alternative ways of producing a joint-detction event between distant photodetectors. Type-two ghost imaging uses chaotic-thermal light. The type-two image-forming correlation is the result of interferences between paired two-photon amplitudes, corresponding to two different yet indistinguishable alternative ways of triggering a join-detection event by two independent photons. A great deal of confusion about ghost imaging comes from "ghost shadow". Similar to x-ray photography, a ghost shadow can be made in coincidences by "blocking-partial blocking-unblocking" of either co-rotating laser beams or classically correlated "speckles". "Ghost shadow" is indeed a classical phenomenon. The physics of ghost imaging, however, is fundamentally different. This article is aimed at exploring the nonlocal two-photon interference nature of ghost imaging.