Controlling the expansion of a dipolar BEC of NaCs molecules

Starting from a dipolar BEC of NaCs molecules [1], we observe the BEC expansion in time-of-flight. We find that it substantially deviates from the expansion of a non-dipolar condensate. By changing the microwave fields that shield the molecules, we tune the orientation and magnitude of the effective dipole moment induced in the molecules. We compare the observed expansion to an ab-initio calculation using a variational Gaussian ansatz and to numerical solutions of the extended Gross-Pitaevskii equation. Our models take into account the induced dipole moment and the s-wave scattering length as obtained from coupled channel calculations. We find good agreement between the theory and the experimental results.

[1] “Observation of Bose-Einstein condensation in a gas of dipolar molecules,” Bigagli, N., Yuan, W., Zhang, S., Bulatovic, B., Karman, T., Stevenson, I., Will, S., arXiv:2312.10965 (2023).