Spectroscopy of bulk excitations in a supersolid-like Bose-Einstein condensate

The supersolid state -- a state which is simultaneously superfluid and crystalline -- is a new frontier in the study of quantum states of matter. Speculated to exist in a diverse set of systems stretching from superfluid helium to neutron stars, supersolid-like states have recently been demonstrated with ultracold atoms. In our experiment we prepare a Bose-Einstein condensate (BEC) in a Raman-dressed dispersion which produces a roton mode characteristic of a supersolid state. The application of a weak optical lattice explicitly breaks translational symmetry, coupling to the roton mode and inducing strong crystalline order. In this work we explore the various ways that this implementation allows us to probe the low-energy excitation spectrum of such a state and demonstrate the connection between the explicit symmetry breaking and a gap in the excitation spectrum. This controlled environment for producing a gapped supersolid provides a complementary approach to exploring low-energy supersolid excitations in spontaneous supersolids such as the ones demonstrated in dipolar BECs.