Splitting of singly and doubly quantized composite vortices in two-component Bose-Einstein condensates

We study numerically the dynamical instabilities and splitting of singly and doubly quantized composite vortices in two-component Bose-Einstein condensates harmonically confined to quasi two dimensions. In this system, the vortices become pointlike composite defects that can be classified in terms of an integer pair (kappa(1), kappa(2)) of phase winding numbers. Our simulations based on zero-temperature mean-field theory reveal several vortex splitting behaviors that stem from the multicomponent nature of the system and do not have direct counterparts in single-component condensates. By calculating the Bogoliubov excitations of stationary axisymmetric composite vortices, we find nonreal excitation frequencies (i.e., dynamical instabilities) for the singly quantized (1, 1) and (1, -1) vortices and for all variants of doubly quantized vortices, which we define by the condition max(j=1,2) vertical bar kappa(j)vertical bar= 2. While the short-time predictions of the linear Bogoliubov analysis are confirmed by direct time integration of the Gross-Pitaevskii equations of motion, the time integration also reveals intricate long-time decay behavior not captured by the linearized dynamics. First, the (1, +/- 1) vortex is found to be unstable against splitting into a (1, 0) vortex and a (0, +/- 1) vortex. Second, the (2, 1) vortex exhibits a two-step decay process in which its initial splitting into a (2, 0) vortex and a (0, 1) vortex is followed by the off-axis splitting of the (2, 0) vortex into two (1, 0) vortices. Third, the (2, -2) vortex is observed to split into a (-1, 1) vortex, three (1, 0) vortices, and three (0, -1) vortices. Each of these splitting processes is the dominant decay mechanism of the respective stationary composite vortex for a wide range of intercomponent interaction strengths and relative populations of the two condensate components and should be amenable to experimental detection. Our results contribute to a better understanding of vortex physics, hydrodynamic instabilities, and two-dimensional quantum turbulence in multicomponent superfluids.Peer reviewe