title: Bose-Glass phases of ultracold atoms due to cavity backaction.
abstract: We determine the quantum ground-state properties of ultracold bosonic atoms interacting with the mode of a high-finesse resonator. The atoms are confined by an external optical lattice, whose period is incommensurate with the cavity mode wavelength, and are driven by a transverse laser, which is resonant with the cavity mode. While for pointlike atoms photon scattering into the cavity is suppressed, for sufficiently strong lasers quantum fluctuations can support the buildup of an intracavity field, which in turn amplifies quantum fluctuations. The dynamics is described by a Bose-Hubbard model where the coefficients due to the cavity field depend on the atomic density at all lattice sites. Quantum Monte Carlo simulations and mean-field calculations show that, for large parameter regions, cavity backaction forces the atoms into clusters with a checkerboard density distribution. Here, the ground state lacks superfluidity and possesses finite compressibility, typical of a Bose glass. This system constitutes a novel setting where quantum fluctuations give rise to effects usually associated with disorder.
authors.affiliation: Theoretische Physik, Universität des Saarlandes, D-66123 Saarbrücken, Germany and Departament de Física, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Spain.
authors.forename: Hessam
authors.initials: H
authors.lastname: Habibian
authors.affiliation: Theoretische Physik, Universität des Saarlandes, D-66123 Saarbrücken, Germany.
authors.forename: André
authors.initials: A
authors.lastname: Winter
authors.affiliation: Departament de Física, Universitat Autònoma de Barcelona, E-08193 Bellaterra, Spain.
authors.forename: Simone
authors.initials: S
authors.lastname: Paganelli
authors.affiliation: Theoretische Physik, Universität des Saarlandes, D-66123 Saarbrücken, Germany.
authors.forename: Heiko
authors.initials: H
authors.lastname: Rieger
authors.affiliation: Theoretische Physik, Universität des Saarlandes, D-66123 Saarbrücken, Germany.
authors.forename: Giovanna
authors.initials: G
authors.lastname: Morigi