In a combined theory and experimental work, we study the elementary excitations of trapped dipolar quantum gases crossing from regular superfluid to supersolid. Our work is now published in PRL and summarized in the Synopsis by Sophia Chen.
Theoretically, we show that, when entering the supersolid phase, two distinct excitation branches appear, respectively associated with dominant crystal and superfluid excitations. We show that their respective crystal and superfluid characters, expected in infinite systems, persist in the laboratory systems. Experimentally, we excite the supersolid state by a sudden reduction of the trap confinement. In the normal superfluid, this excitation scheme is affecting a single compressional mode whereas multiple modes in the supersolid regime are populated. Here, the multiple modes separate in energy and form two branches, in agreement with theoretical predictions. These spectral measurements lay the foundations for future studies of superfluidity in supersolid dipolar gases.