Mainz 2017 – scientific programme

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A: Fachverband Atomphysik

A 7: Ultracold atoms and BEC - II (with Q)

A 7.3: Talk

Monday, March 6, 2017, 17:30–17:45, N 1

supersolidity in a Bose-Einstein condensate — •Andrea Morales, Julian Leonard, Philip Zupancic, Tilman Esslinger, and Tobias Donner — 1Institute for Quantum Electronics, ETH Zürich, Switzerland

Supersolidity is a paradoxical state of matter featuring both the crystalline order of a solid and the dissipationless flow typical of a superfluid. The realization of this state of matter requires the breaking of two continuous symmetries, the phase invariance of a superfluid and the translational invariance to form the crystal. Proposed for Helium almost 50 years ago, experimental verification of supersolidity remained elusive. Here we report on the realization of such a supersolid state of matter.

This state is realized by coupling a Bose-Einstein condensate (BEC) to the modes of two crossed optical cavity modes. Self-organization to individual cavities only breaks a discrete spatial symmetry and realizes a *lattice supersolid*. By equally coupling the BEC to both modes we enhance the symmetry of the system to a continuous one and observe simultaneous self-organization to the two cavities. We measure the high ground state degeneracy of the new supersolid state by measuring the crystal position over many realizations through the light fields leaking from the cavities. We also monitor real time fluctuations in the crystal position by the relative change in the light levels.