Arxiv Selection Jun 2019

Jun 1-Jun 7 Sayan Choudhury, Jun 8-Jun 14 Zehan Li, Jun 15- Jun 21 Jiansong Pan, Jun 22- Jun 28 Ahmet Keles

Jun 10

arXiv:1906.02791 [pdf]

Supersolid symmetry breaking from compressional oscillations in a dipolar quantum gas

L. Tanzi, S. M. Roccuzzo, E. Lucioni, F. Famà, A. Fioretti, C. Gabbanini, G. Modugno, A. Recati, S. Stringari

The existence of a paradoxical supersolid phase of matter, possessing the apparently incompatible properties of crystalline order and superfluidity, was predicted 50 years ago1-3 . Solid helium was the natural candidate, but there supersolidity has not been observed yet, despite numerous attempts4-7 . Ultracold quantum gases have recently shown the appearance of the periodic order typical of a crystal, due to various types of controllable interactions8-12 . A crucial feature of a Ddimensional supersolid is the occurrence of up to D+1 gapless excitations reflecting the Goldstone modes associated with the spontaneous breaking of two continuous symmetries: the breaking of phase invariance, corresponding to the locking of the phase of the atomic wave functions at the origin of superfluid phenomena, and the breaking of translational invariance due to the lattice structure of the system. The occurrence of such modes has been the object of intense theoretical investigations1,13-17, but their experimental observation is still missing. Here we demonstrate the supersolid symmetry breaking through the appearance of two distinct compressional oscillation modes in a harmonically trapped dipolar Bose-Einstein condensate, reflecting the gapless Goldstone excitations of the homogeneous system. We observe that the two modes have different natures, with the higher frequency mode associated with an oscillation of the periodicity of the emergent lattice and the lower one characterizing the superfluid oscillations. Our work paves the way to explore the two quantum phase transitions between the superfluid, supersolid and solid-like configurations that can be accessed by tuning a single interaction parameter.

Jun 9

arXiv:1906.03185 [pdf, other]

Homogeneous Floquet time crystal protected by gauge invariance

Angelo Russomanno, Simone Notarnicola, Federica Maria Surace, Rosario Fazio, Marcello Dalmonte, Markus Heyl

Comments: 6 pages and 4 figures + 3 pages and 3 figures of Supplementary Information

Subjects: Quantum Gases (cond-mat.quant-gas); Quantum Physics (quant-ph)

We show that homogeneous lattice gauge theories can realize nonequilibrium quantum phases with long-range spatiotemporal order protected by gauge invariance instead of disorder. We study a kicked Z2-Higgs gauge theory and find that it breaks the discrete temporal symmetry by a period doubling. In a limit solvable by Jordan-Wigner analysis we extensively study the time-crystal properties for large systems and further find that the spatiotemporal order is robust under the addition of a solvability-breaking perturbation preserving the Z2 gauge symmetry. The protecting mechanism for the nonequilibrium order relies on the Hilbert space structure of lattice gauge theories, so that our results can be directly extended to other models with discrete gauge symmetries.