It is well known that totally incoherent light cannot exhibit first-order interference with photons that are uncorrelated,
i.e., the normalized first-order correlation function is g(1)(0) = 0, whereas the second-order correlation
function is g(2)(0) = 1. Less familiar is the fact that both chaotic and coherent sources can exhibit first-order interference,
so that merely using the term "interference" is ambiguous. If fact, some previous QIQC presentations
have centered around whether or not two-photon correlations are actually a form of two-photon interference.1
Another area of ambiguity concerns the detection of quantum state coherence using interference.2 In an attempt
to disambiguate the concept of interference, we examine associated photon states using chaotic sources and the
Hanbury Brown and Twiss (HBT) detection of bunched photons. The unambiguous determination of coherent
quantum states has important applications for:
(1) Atomic Bose-Einstein condensate (BEC) determined using scattered laser interference3
(2) Exciton-Polariton BEC determined using emitted photon interference4
(3) Coherent light states.
(4) Characterizing photon statistics.
(5) Characterization of extended sources.
In this paper, we present imaging results for topics 3-5. The difficulties of HBT data acquisition are generally
underappreciated. An advantage of our approach is super-linear speedup through the development of a new
imaging device consisting of a 2-dimensional array of single-photon avalanche detectors.5, 6 A 4 × 4 array
enables 120 HBT coincidence experiments to be run in parallel to generate the 2-dimensional distribution of
g(2)(x) spatial correlations, thus making plausible the term "g2 camera" for this quantum imaging device.