Bound solitons in the ac-driven, damped nonlinear Schrödinger equation

We demonstrate analytically that the effective potential of interaction between widely separated solitons in a damped, ac-driven nonlinear Schrödinger equation is oscillatory at large distances. We show numerically that two solitons in the system attract each other if the initial distance between them is smaller than a certain critical value; consequently, they will either form an oscillatory bound state with a finite lifetime, collapse to a stable single soliton state, or decay to the rotating background. If the initial separation is greater than the critical value, they separate to form a stable bound state at a second critical distance. The critical distances are in good agreement with the analytical prediction.