Quantum disordered dynamics in the arrested relaxation of a molecular ultracold plasma

Spontaneous avalanche to plasma splits the core of an ellipsoidal Rydberg gas of nitric oxide. Ambipolar expansion first quenches the electron temperature of this core plasma. Then, long-range, resonant charge transfer from ballistic ions to frozen Rydberg molecules in the wings of the ellipsoid quenches the centre-of-mass ion/Rydberg molecule velocity distribution. This sequence of steps gives rise to a remarkable mechanics of self-assembly, in which the kinetic energy of initially formed hot electrons and ions drives an observed separation of plasma volumes. After 300 ns, electron collisional transport processes stop, and the distribution of electron binding energies relaxes to a narrow band just below the ionization threshold. The long lifetime of this system with respect to recombination and neutral dissociation, suggests that this transformation affords a robust state of arrested relaxation, far from thermal equilibrium. We argue that this state of the quenched ultracold plasma offers an experimental platform for studying quantum many-body physics of disordered systems in the long-time and finite energy-density limits.