Hanbury Brown and Twiss measurements in curved space

Abstract

Hanbury Brown and Twiss measurements on speckle patterns propagating along curved surfaces improve understanding of spatial coherence. When Hanbury Brown and Twiss (HBT) proposed their technique of intensity correlation measurements1,2,3 to examine the angular size of stars in the visible range, they challenged the common conception of quantum mechanics and kicked off a discussion that led to the establishment of quantum optics4,5,6. In this Letter we revisit this fundamental technique and study its implications in the presence of space curvature. To this end we theoretically and experimentally investigate the evolution of speckle patterns propagating along two-dimensional surfaces of constant positive and negative Gaussian curvature, defying the notion that light always gains spatial coherence during free-space propagation. We also discuss the measurability of the traversed space's curvature utilizing HBT from an inhabitant's point of view. Through their symmetry, surfaces with constant Gaussian curvature act as analogue models for universes possessing non-vanishing cosmological constants.