Possible Many-Body Localization in a Long-Lived Finite-Temperature Ultracold Quasineutral Molecular Plasma

We argue that the quenched ultracold plasma presents an experimental platform for studying the quantum many-body physics of disordered systems in the long-time and finite energy-density limits. We consider an experiment that quenches a plasma of nitric oxide to an ultracold system of Rydberg molecules, ions, and electrons that exhibits a long-lived state of arrested relaxation. The qualitative features of this state fail to conform with classical models. Here, we develop a microscopic quantum description for the arrested phase based on an effective many-body spin Hamiltonian that includes both dipole-dipole and van der Waals interactions. This effective model appears to offer a way to envision the essential quantum disordered nonequilibrium physics of this system.

Figure 1

(a) Double-resonant selection of the initial quantum state of the $n_{0}f(2)$ Rydberg gas. (b) Laser-crossed differentially pumped supersonic molecular beam. (c) Selective field ionization spectrum after a 500 ns evolution, showing the signal of weakly bound electrons combined with a residual population of $49f(2)$ Rydberg molecules. After $10\mu \mathrm{s}$, this population sharpens to signal only high-$n$ Rydberg molecules and plasma electrons. (d) Integrated electron signal as a function of evolution time from 0 to $160\mu \mathrm{s}$. Note the onset of the arrested phase before $10\mu \mathrm{s}$. Time scale compressed by a factor of 2 after $80\mu \mathrm{s}$. (e) $x$, $y$-integrated images recorded after a flight time of $400\mu \mathrm{s}$ with $n_0=40$ for initial Rydberg gas peak densities varying from $2\times {10}^{11}$ to $1\times {10}^{12}{\mathrm{cm}}^{-3}$. All of these images exhibit the same peak density: $1\times {10}^7{\mathrm{cm}}^{-3}$.

Figure 2

Schematic representation of ${\mathrm{NO}}^{+}$ core ions, paired with extravalent electrons to form interacting dipoles ${\mathbf{d}}_i$ and ${\mathbf{d}}_j$, separated by ${\mathbf{r}}_{ij}={\mathbf{r}}_i-{\mathbf{r}}_j$.