Phase coherence and dynamical crystallization in attractive 1D Bose gases

Unveiling non-equilibrium instability dynamics of a many-body system is a current frontier across diverse fields. Low-dimensional quantum gases offer a versatile platform for studying microscopic details of instability-induced dynamics. An intriguing example is modulation instability (MI), which emerges when the interaction is quenched from repulsive to attractive. It is commonly known that MI amplifies initial density fluctuations, resulting in the formation of solitonic excitations observed in one-dimensional (1D) and two-dimensional (2D) quantum gases. In this talk, we present the first observation of multi-mode breather excitations resulting from the nonlinear stage of MI seeded by quantum and thermal fluctuations. We prepare two parallel quasi-1D gases in an integrability-preserving box potential. By performing both in-situ and interferometric imaging of two quenched samples, we directly measure density and phase modulations along the samples. Unlike phase-incoherent solitonic excitations, we observe a form of dynamical crystallization in which periodic density modulations recur dynamically in a time-evolution intertwined with reduction and recovery of global phase coherence. At longer times, we show that a dephased 1D gas can regain phase coherence after the interaction is ramped back to repulsion without significant atom losses. Those series of observations open a pathway to investigate very rich MI-induced dynamics, ranging from breathers to phase transition across zero scattering length.