"From strongly interacting Bose-Fermi mixtures to ultracold dipolar molecules"
Atoms and molecules in the ultracold regime have emerged as promising platforms for quantum simulation and precision measurement. In this talk, I will describe our efforts to realize a paradigmatic quasiparticle in condensed matter physics—the Bose polaron—using an ultracold mixture of bosonic and fermionic atoms. The polaron was proposed by Landau to describe the dynamics of an electron coupled to the phonons of a crystal. We created the polaron by immersing a minority of 40K into a BEC of 23Na, tuned the interspecies interaction by a Feshbach resonance, and measured the polaron’s energy and spectral width as a function of temperature via radiofrequency spectroscopy. At low temperatures and unitary interaction strengths, the polaron enters the “quantum critical” regime, where all energy scales except temperature vanish and the simple quasiparticle picture breaks down.
Going beyond atoms, molecules have far richer internal structures and more tunable interactions, yet coherent control over their degrees of freedom presents an experimental challenge. I will describe progress in creating and controlling an ultracold dipolar gas of 23Na40K. At the single-molecule level, we performed microwave spectroscopy on the lowest rotational manifolds of NaK’s electronic ground state, culminating in a demonstration of a second-scale spin coherence time between two nuclear spin states via Ramsey spectroscopy. Controlling NaK-NaK interactions was the natural further step. Through the technique of microwave dressing, we enhanced the scattering between NaK molecules by three orders of magnitude compared to the background van der Waals scattering, upon inducing dipolar interactions. This approach is general, providing an ideal way to tune interactions in all dipolar molecules.
Zoe is currently a Graduate Research Assistant at Massachusetts Institute of Technology. Her research interests include quantum many-body physics, molecular physics, and quantum information science.