Measurement of the binding energy of ultracold $^{87}$Rb$^{133}$Cs molecules using an offset-free optical frequency comb

TL;DR

This paper precisely measures the binding energy of ultracold $^{87}$Rb$^{133}$Cs molecules in their ground state using an advanced optical frequency comb, achieving the most accurate dissociation energy to date.

Contribution

It introduces an offset-free optical frequency comb technique combined with STIRAP to measure molecular binding energies with unprecedented accuracy.

Findings

Binding energy of $^{87}$Rb$^{133}$Cs$ in the ground state determined as $h\times114,268,135,237(5)(50)$ kHz.

Achieved 88% transfer efficiency in creating molecules in the ground state.

Resolutions of 5 kHz over 114 THz energy difference, resolving hyperfine structure.

Abstract

We report the binding energy of $^{87}$Rb$^{133}$Cs molecules in their rovibrational ground state measured using an offset-free optical frequency comb based on difference frequency generation technology. We create molecules in the absolute ground state using stimulated Raman adiabatic passage (STIRAP) with a transfer efficiency of 88\%. By measuring the absolute frequencies of our STIRAP lasers, we find the energy-level difference from an initial weakly-bound Feshbach state to the rovibrational ground state with a resolution of 5 kHz over an energy-level difference of more than 114 THz; this lets us discern the hyperfine splitting of the ground state. Combined with theoretical models of the Feshbach state binding energies and ground-state hyperfine structure, we determine a zero-field binding energy of $h\times114\,268\,135\,237(5)(50)$ kHz. To our knowledge, this is the most accurate determination to date of the dissociation energy of a molecule.