Phase transitions of an ultracold gas in a quasicrystalline potential

Yogesh Sharad Patil, Hil Fung Harry Cheung, Mukund Vengalattore

R. Hanai, T. Kashimura, R. Watanabe +2 more

Dean Johnstone, Patrik Öhberg, Callum W. Duncan

The ground-state properties of an ultracold Bose gas in an eightfold symmetric lattice are studied. Mott-insulator, density wave, and supersolid phases are identified. A density wave phase that spontaneously breaks rotational symmetry appears for strong long-range interactions.

Farokh Mivehvar, Helmut Ritsch, Francesco Piazza

The discovery of quasicrystals with crystallographically forbidden rotational symmetries has changed the notion of the ordering in materials, yet little is known about the dynamical emergence of such exotic forms of order. Here we theoretically study a nonequilibrium cavity-QED setup realizing a zero-temperature quantum phase transition from a homogeneous Bose-Einstein condensate to a quasicrystalline phase via collective superradiant light scattering. Across the superradiant phase transition, collective light scattering creates a dynamical, quasicrystalline optical potential for the atoms. Remarkably, the quasicrystalline potential is "emergent" as its eightfold rotational symmetry is not present in the Hamiltonian of the system, rather appears solely in the low-energy states. For sufficiently strong two-body contact interactions between atoms, a quasicrystalline order is stabilized in the system, while for weakly interacting atoms the condensate is localized in one or few of the deepest minima of the quasicrystalline potential.

W. Vincent Liu

Youssef Kora, Massimo Boninsegni

We study by quantum Monte Carlo simulations the low-temperature phase diagram of dipolar bosons confined to one dimension, with dipole moments aligned along the direction of particle motion. A hard-core repulsive potential of varying range ($\ensuremath{\sigma}$) is added to the dipolar interaction, in order to ensure stability of the system against collapse. In the $\ensuremath{\sigma}\ensuremath{\rightarrow}0$ limit the physics of the system is dominated by the potential energy and the ground state is quasicrystalline; as $\ensuremath{\sigma}$ is increased the attractive part of the interaction weakens and the equilibrium phase evolves from quasicrystalline to a nonsuperfluid liquid. At a critical value ${\ensuremath{\sigma}}_{c}$, the kinetic energy becomes dominant and the system undergoes a quantum phase transition from a self-bound liquid to a gas. In the gaseous phase with $\ensuremath{\sigma}\ensuremath{\rightarrow}{\ensuremath{\sigma}}_{c}$, at low density attractive interactions bring the system into a ``weak'' superfluid regime. However, gas-liquid coexistence also occurs, as a result of which the topologically protected superfluid regime is not approached.