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Dissipation-induced structural instability and chiral dynamics in a quantum gas

Chirality by dissipation Quantum many-body systems can display exotic dynamics in the presence of dissipation. Dogra et al. studied such dynamics in a system consisting of an atomic Bose-Einstein condensate located in an optical cavity and exposed to a standing wave of laser light. Light scattering off the atomic cloud and into the cavity resulted in two distinct, spatially patterned collective modes for the atoms. When the researchers then introduced dissipation to couple the two modes, the system followed a directed circular path through phase space, rotating between the modes. Science, this issue p. 1496 Chiral dynamics emerge in an atomic Bose-Einstein condensate in an optical cavity in the presence of dissipation. Dissipative and unitary processes define the evolution of a many-body system. Their interplay gives rise to dynamical phase transitions and can lead to instabilities. In this study, we observe a nonstationary state of chiral nature in a synthetic many-body system with independently controllable unitary and dissipative couplings. Our experiment is based on a spinor Bose gas interacting with an optical resonator. Orthogonal quadratures of the resonator field coherently couple the Bose-Einstein condensate to two different atomic spatial modes, whereas the dispersive effect of the resonator losses mediates a dissipative coupling between these modes. In a regime of dominant dissipative coupling, we observe the chiral evolution and relate it to a positional instability.