LAUSR

Emission of matter wave jets has been recently observed in a Bose-Einstein condensate confined by a cylindrical box potential, induced by a periodically modulated inter-particle interaction (Nature {\bf 551}, 356 (2017)). In this letter we apply the time-dependent Bogoliubov theory to study the correlation effect observed in this highly non-equilibrium phenomenon. Without any fitting parameter, our theoretical calculations on the angular density correlations are in excellent quantitative agreement with the experimental measurements. We interpret the angular density correlation of the jets as the Hanbury-Brown-Twiss effect between the excited quasi-particles with different angular momenta, and our theory explains the puzzling observation of the asymmetric density correlations between the jets with the same and opposite momenta. Our theory can also identify the main factors that control the height and width of the peaks in the density correlation function, which can be directly verified in future experiments.