Lifetimes of ultra-long-range strontium Rydberg molecules

The lifetimes of the lower-lying vibrational states of ultra-long-range strontium Rydberg molecules comprising one ground-state $5s^2$ ${}^1{S}_0$ atom and one Rydberg atom in the $5s38s{}^3{S}_1$ state are reported. The molecules are created in an ultracold gas held in an optical dipole trap and their numbers determined using field ionization, the product electrons being detected by a microchannel plate. The measurements show that, in marked contrast to earlier measurements involving rubidium Rydberg molecules, the lifetimes of the low-lying molecular vibrational states are very similar to those of the parent Rydberg atoms. This results because the strong $p$-wave resonance in low-energy electron-rubidium scattering, which strongly influences the rubidium molecular lifetimes, is not present for strontium. The absence of this resonance offers advantages for experiments involving strontium Rydberg atoms as impurities in quantum gases and for testing of theories of molecular formation and decay.

Figure 1

Schematic of the timing sequence used to determine lifetimes.

Figure 2

Measured Rydberg excitation spectrum (the parent 38 ${}^3{S}_1$ feature is attenuated by a factor of 10). Calculated positions and relative excitation strengths for the $\nu =0$, 1, and 2 molecular vibrational states are indicated by vertical bars. The small additional feature at a binding energy of 8 MHz is attributed to trimer formation (see text).

Figure 3

Calculated molecular potential (black) and calculated wave functions for the $\nu =0$ (red line), 1 (green line), and 2 (blue line) molecular vibrational states.

Figure 4

SFI spectra measured for the parent 38 ${}^3{S}_1$ Rydberg state and for the $\nu =0$, 1, and 2 molecular states with a delay time $t_D=0$. Spectra are normalized to the same total area.

Figure 5

Evolution of the SFI spectrum for (a) the parent 38 ${}^3{S}_1$ Rydberg state and (b) the $\nu =0$ molecular vibrational state as a function of delay time. Values of the various delay times used are as indicated. Arrows indicate the $n$ values of ${}^3\mathrm{P}$ states populated by BBR-induced transitions.

Figure 6

Evolution of the population of 38 ${}^3{S}_1$ Rydberg atoms and of the molecular $\nu =0$, 1, and 2 vibrational states as a function of the time delay $t_D$. Data sets are each normalized to 1 at $t_D=0$.

Figure 7

Measured decay rates ${\gamma }_{\mathrm{TOT}}$ as a function of the average trap density. Straight-line fits to the data are included.