Ole Rømer Colloquium Wednesday 15 August at 15.15 in Fys. Aud. Speaker: Tilman Esslinger, Institute for Quantum Electronics, ETH Zurich, Switzerland Host: Thomas Pohl Title: Supersolid Higgs and Goldstone Modes Abstract: The concept of a supersolid state is paradoxical. It combines the crystallization of a many-body system with dissipationless flow of the atoms it is built of. This phase requires the breaking of two symmetries, the phase invariance of a superfluid and the translational invariance to form the crystal. I will report on a quantum simulation experiment in which we realized a supersolid phase breaking a continuous translational symmetry along one direction. It emerges from two discrete spatial symmetries by symmetrically coupling a Bose-Einstein condensation to the modes of two optical cavities. The collective excitations of the system have the nature of Higgs and Goldstone modes. The amplitudes of the field of the two optical cavities form real and imaginary part of a U(1)-symmetric order parameter. Monitoring the cavity fields in real-time allows us to observe the dynamics of the associated Higgs and Goldstone modes and reveal their amplitude and phase nature. We use a spectroscopic method to measure their frequencies and give a tunable mass to the Goldstone mode at the crossover between continuous and discrete symmetry. Our experiments provide a link between previous spectroscopic measurements and the theoretical concept of Higgs and Goldstone modes. Coffee and cake will be available from 15.05