Photoassociative Spectroscopy of a Halo Molecule in $^{86}$Sr

TL;DR

This study measures the binding energy of a halo molecule in $^{86}$Sr, providing precise scattering length data and demonstrating potential for optical manipulation of atom interactions and Efimov state exploration.

Contribution

First measurement of a halo state in $^{86}$Sr, refining scattering length with high accuracy and highlighting optical control possibilities.

Findings

Measured binding energy of -83.00 kHz for the halo molecule.

Determined scattering length as 810.6 a_0 with high precision.

Indicated potential for optical manipulation and Efimov physics in $^{86}$Sr.

Abstract

We present two-photon photoassociation to the least-bound vibrational level of the X$^1\Sigma_g^+$ electronic ground state of the $^{86}$Sr$_2$ dimer and measure a binding energy of $E_b=-83.00(7)(20)$\,kHz. Because of the very small binding energy, this is a halo state corresponding to the scattering resonance for two $^{86}$Sr atoms at low temperature. The measured binding energy, combined with universal theory for a very weakly bound state on a potential that asymptotes to a van der Waals form, is used to determine an $s$-wave scattering length $a=810.6(12)$\,$a_0$, which is consistent with, but substantially more accurate than the previously determined $a=798(12)\,a_0$ found from mass-scaling and precision spectroscopy of other Sr isotopes. For the intermediate state, we use a bound level on the metastable $^1S_0-{^3P_1}$ potential. Large sensitivity of the dimer binding energy to light near-resonant with the bound-bound transition to the intermediate state suggests that $^{86}$Sr has great promise for manipulating atom interactions optically and probing naturally occurring Efimov states.