Soliton "molecules": robust clusters of light bullets

This paper considers the propagation of two-colour (fundamental wave and second harmonic) light bullets "molecules" in a bulk dispersive medium with competing quadratic and cubic (Kerr) self-defocusing nonlinearities. This study also investigates the circular light-bullet necklaces, constructed as superposition of N fundamental spatio-temporal solitons with different phases such that the overall phase jump around the core is a multiple of 2π. Although this work demonstrates the key concepts for the example of light waves, this study is crucially important for other fields such as the physics of hybrid atom-molecular Bose-Einstein condensates.