Narrow-line photoassociation spectroscopy and mass-scaling of bosonic strontium

Abstract

Using new experimental measurements of photoassociation resonances near the ${}^1{\mathrm{S}}_0\to {}^3{\mathrm{P}}_1$ intercombination transition in ${}^{84}$Sr and ${}^{86}$Sr, we present an updated study into the mass-scaling behavior of bosonic strontium dimers. A previous mass-scaling model [Borkowski et al., Phys. Rev. A 90, 032713 (2014)] was able to incorporate a large number of photoassociation resonances for ${}^{88}$Sr, but at the time only a handful of resonances close to the dissociation limit were known for ${}^{84}$Sr and ${}^{86}$Sr. In this work, we perform a more thorough measurement of ${}^{84}$Sr and ${}^{86}$Sr bound states, identifying multiple new resonances at deeper binding energies out to $E/h=-5$ GHz. We also identify several previously measured resonances that cannot be experimentally reproduced and provide alternative binding energies instead. With this improved spectrum, we develop a mass-scaled model that reproduces the observed binding energies of ${}^{86}$Sr and ${}^{88}$Sr to within 1 MHz. In order to accurately reproduce the deeper bound states, our model includes a second $1_u$ channel and more faithfully reproduces the depth of the potential. As determined by the previous mass-scaling study, ${}^{84}$Sr $0_u^{+}$ levels are strongly perturbed by the avoided crossing between the ${}^1{\mathrm{S}}_0+{}^3{\mathrm{P}}_1$ $0_u^{+}$ ${(}^3{\Pi }_u)$ and ${}^1{\mathrm{S}}_0+{}^1{\mathrm{D}}_2$ $0_u^{+}$ ${(}^1{\Sigma }_u^{+})$ potential curves and therefore are not included in this mass-scaled model, but are accurately reproduced using an isotope-specific model with slightly different quantum defect parameters. In addition, the optical lengths of the ${}^{84}$Sr $0_u^{+},\nu =-2$ to $\nu =-5$ states are measured and compared to numerical estimates to characterize their use as optical Feshbach resonances.

Corrected typo in metadata 9 pages, 3 figures