**July 20 2015**

**20.-22.07.2015: Visit of Nishant Dogra**

Nishant Dogra (Quantum Optics Group, ETH Zurich) is visiting us and will give a talk in our Ctrl-q seminar on Wednesday 22.07.2015 at 9.00 o'clock in E.04 about "Bose-Hubbard model with cavity-mediated long-range interactions: theory and experiment".

Abstract:

The Bose-Hubbard model has been a paramount example of quantum simulation of many-body

systems. It is realized by loading a quantum gas in a 3D optical lattice. This system undergoes a

quantum phase transition from a superfluid to a Mott-insulator phase due to the competition

between the kinetic energy and the short-range interactions. We study the effect of long-range

interactions on this system generated by strongly coupling the quantum gas to a high finesse cavity

and pumping it with a transverse laser field. This system can be mapped to an extended BoseHubbard

model. In the limit where the static lattices are commensurate with the cavity generated

dynamical lattice, we calculate the phase diagram of this system using a mean-field method. We find

that the cavity-mediated long-range interactions give rise to additional phases: charge density wave

and supersolid phase. We also calculate the excitation spectrum of these phases using a slave-Boson

approach and relate it to the nature of the transition between them. We also show the recent

experimental progress in observing the charge density wave and mapping the phase diagram of such

a system as a function of short-range and cavity-mediated long-range interactions.