Hanbury Brown and Twiss correlations in atoms scattered from colliding condensates

Low energy elastic scattering between clouds of Bose condensed atoms leads to the well known $s$-wave halo with atoms emerging in all directions from the collision zone. In this paper we discuss the emergence of Hanbury Brown and Twiss coincidences between atoms scattered in nearly parallel directions. We develop a simple model that explains the observations in terms of an interference involving two pairs of atoms each associated with the elementary $s$-wave scattering process.

Figure 1

(Color online) Diagrammatic representation of two condensates colliding and giving rise to an s-wave halo of scattered particles. Particles are scattered pairwise back-to-back.

Figure 2

(Color online) State of four atoms, scattered pairwise back-to-back. Atoms detected by detectors A and B in an arbitrary pair of directions have partners recoiling in the opposite directions within a certain width imposed by the uncertainty on total and relative momentum of the atoms. The quantum state of the detected pair is obtained by a partial trace over the recoiling momentum components, and the coincidence counting yield in the detectors is just the product of the single detector count signals

Figure 3

(Color online) State of four atoms, with two atoms detected in nearly parallel directions. The detected atoms are not unambiguously identified with their recoiling partners if their momentum distributions are wide enough to overlap. This leads to an interference term in the coincidence counting yield in detectors A and B as expressed by the formal expression (13).