Arrested relaxation in an isolated molecular ultracold plasma

Abstract

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. These dynamics adiabatically sequester energy in a reservoir of mass transport, starting a process that anneals separating volumes to form an apparent glass of strongly coupled ions and electrons. Short-time electron spectroscopy provides experimental evidence for complete ionization. The long lifetime of this system, particularly its stability with respect to recombination and neutral dissociation, suggests that this transformation affords a robust state of arrested relaxation, far from thermal equilibrium.

Many-body physics with ultracold plasmas: quenched randomness and localization

“…This Rydberg gas density fluctuates, but we have managed to calibrate a measure of the sum of counts in each SFI trace to classify the corresponding initial density of every shot. Coupled rate simulations that describe the kinetics of the avalanche of Rydberg gas to plasma conform well with the observed evolution in electron binding energy as a function of Rydberg gas density estimated in this way [38,40].…”

“…We see these dynamics directly in three-dimensional images of plasma bifurcation [37,38]. Here, the acceleration of opposing plasma volumes disposes kinetic energy initially present in the electron gas.…”

“…On a microsecond timescale, this plasma bifurcates, irreversibly disposing electron energy to a reservoir of mass transport [37]. This evidently quenches the system to form an ultracold, quasi-neutral plasma in a state of arrested relaxation, far from thermal equilibrium [38]. Classical models for plasma rate processes that describe the initial stages of Rydberg gas avalanche and plasma dissipation fail to account for the long lifetime and low electron temperature of this system [34,39,40].…”

Coupled rate-equation hydrodynamic simulation of a Rydberg gas Gaussian ellipsoid: Classical avalanche and evolution to molecular plasma

“…Consequently, the ions and electrons undergo a second-order decay driven by dissociative recombination, which converts electrons into N( 4 S)+O( 3 P). [40]. These characteristics suggest a state of Rydberg gas with an average principal quantum number of n 0 = 80, or a plasma of NO + ions and electrons with a T e ≤ 5 K. This ellipsoid has measured Gaussian dimensions of σ x = 1.0 mm, σ y = 0.55 mm and σ z = 0.70 mm.…”

“…The laser crossed molecular beam illumination volume creates a nonuniform Rydberg gas, distributed as a Gaussian ellipsoid. The consequences of this initial condition appear in its evident effect on the evolution dynamics [40]. In the present paper, we develop a reference framework for coupled rate processes that explicitly reckon with the evolution of the kinetic and hydrodynamic processes over a realistic distribution of ion/electron and Rydberg densities.…”