Tunable Interactions in a Long-lived BEC of Dipolar Molecules*

Applications of ultracold dipolar molecules require a collisionally stable, quantum degenerate sample with widely tunable interactions. We demonstrate that dressing the molecules with both sigma+ and pi-microwave fields simultaneously [1, 2] suppresses collisional losses to below the detection limit and enables flexible tuning of the strength of dipolar interactions. We observe lifetimes of the dipolar BEC of up to 2 seconds. Detailed measurements of the loss rates reveal a wide stability window in which the dipole moment can be tuned while the losses remain strongly suppressed. Using the dipolar interactions induced by microwave dressing, we observe electrostriction of a dipolar BEC for the first time, opening the door to studying collective interaction effects in this new dipolar quantum liquid.