Probing a strongly interacting bose mixture with ultralong-range Rydberg molecules*

Recent work has shown that photoexcitation of ultralong range Rydberg molecules (ULRRMs) proivdes an \textit{in situ} probe of spatial correlations in quantum gases. The excitation rate of the ground-state dimer ULRRM is proportional to the nonlocal pair correlation function $g^{(2)}(R)$, with $R$ tunable from roughly $1400-3200$ $a_0$ by changing the principal quantum number, $n$, of the target Rydberg state [1]. At these length scales, the pair correlation function for a weakly interacting gas is largely determined by the thermal de Broglie wavelength and the symmetry of the many-body wavefunction under particle exchange. In the presence of strong interparticle interactions, however, $g^{(2)}(R)$ reflects the shape of the scattering wavefunction at short range, and a node in the wavefunction leads to a zero in the pair-correlation function at a separation around the s-wave scattering length, $a_s$. We present measurements of the excitation rate of ULRRM dimers in a strongly interacting mixture of $^{88}$Sr and $^{84}$Sr ($a_s=1800\,a_0$) and progress in our efforts to observe the effect of strong interactions on the pair correlation function $g^{(2)}(R)$.\\\\$[1]$ J. D. Whalen, et al. Phys. Rev. A \textbf{100}, 011402(R)