Transverse momentum transport and collective-mode localization in dipolar tube arrays

Abstract

We study transverse transport of longitudinal momentum in an array of one-dimensional Bose gases coupled by dipolar interactions without particle tunneling. Within zero-temperature Bogoliubov theory, we characterize this transport using the inter-tube momentum correlator and its squared magnitude, termed amplitude and intensity. In a uniform array, pairs of Bogoliubov quasiparticles propagate ballistically across the tubes, while their dephasing produces a $t^{-3}$ decay of the long-wavelength amplitude. Tube-to-tube density imbalance acts as quenched disorder and localizes the transverse collective modes. At fixed longitudinal momentum, this arrests the growth of the intensity profile, whose time-averaged spatial decay measures the localization length. Equal-time correlations are much less sensitive to disorder and primarily reflect the interaction range: in the uniform array they decay with tube separation as $r^{-7}$ for dipolar coupling, compared with exponential decay for nearest-neighbor coupling. Finally, sufficiently strong inter-tube repulsion destabilizes the longitudinally uniform state toward density modulations staggered between neighboring tubes, at a threshold independent of density imbalance.