Ultracold Atoms Meet Quantum Gravity Boris V. Svistunov, University of Massachusetts Amherst, PHY Little is known precisely about overdamped dynamics in the quantum critical region near zero-temperature. We used Monte Carlo methods to compute universal conductivity of the two-dimensional XY universality class realized at the superfluid-to-Mott insulator point and determined precisely the quantum critical plateau value,  The finite frequency data for  (i  n ) (see figure) were compared to predictions of the holographic gauge/gravity duality theory. We find that it can be made compatible with the data if temperature the black brane horizon is considered as a free parameter; i.e., different from the temperature of the conformal field theory. The requirements for measuring the universal conductivity in a cold gas experiment are also determined by our calculation. Phys. Rev. Lett. 110, (2013); Editors suggestion QUANTUM CRITICAL

Book: “Superfluid States of Matter” Boris V. Svistunov, University of Massachusetts Amherst, PHY The book Superfluid States of Matter by B. Svistunov, E. Babaev, and N. Prokof’ev has been completed and submitted to Taylor and Francis. (To be published in February 2015.) Features Discusses superfluidity and superconductivity in quantum liquids and gases. Takes a simple, modern approach to the subject based on the emergent constant of motion. Gives the basics in state-of-the-art first principle numeric approaches. Separates superfluid properties from quantum properties, allowing for an understanding of all key aspects based on classical-field models.

“Compactified Supersolid Phase of Helium-4” Boris V. Svistunov, University of Massachusetts Amherst, PHY Macroscopic samples of Helium-4 form superfluid, a fluid flowing without friction, at low pressures and they freeze into a crystal at high pressures. As our first principle numerical simulations show, this changes if Helium-4 is confined to small pores of several nanometers wide: solid layers follow the geometrical profile of the pore wall and this results in new phases --- a compactified solid (CS) and a compactified supersolid (CSS). Both phases contain a topological structural defect in their ground state: Frank’s disclination, so far only known to exist in liquid crystals. This disclination possesses a superfluid core in the CSS, which freezes and becomes insulating in the CS at high pressures. The upper picture shows a typical configuration of CSS (on the left) and of the CS (on the right) as viewed along the pore axis. The disordered region in CSS is the superfluid core of the disclination. The lower graph represents superfluid density of the CSS vs applied chemical potential (pressure) obtained in the simulations. L. Pollet and A.B. Kuklov Phys. Rev. Lett. 113, (2013)