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 14

arXiv:1906.05334 [pdf, other]

Strongly Correlated Quantum Gas Prepared by Direct Laser Cooling

Pablo Solano, Yiheng Duan, Yu-Ting Chen, Alyssa Rudelis, Cheng Chin, Vladan Vuletić

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

We create a one-dimensional strongly correlated quantum gas of 133Cs atoms with attractive interactions by direct laser cooling in 300 ms. After compressing and cooling the optically trapped atoms to the vibrational ground state along two tightly confined directions, the emergence of a non-Gaussian time-of-flight distribution along the third, weakly confined direction reveals that the system enters a quantum degenerate regime. We observe a strong reduction of two- and three-body spatial correlations and infer that the atoms are directly cooled into a highly correlated excited metastable state, known as a super-Tonks-Girardeau gas.

Jun 12

arXiv:1906.05011 (cross-list from quant-ph) [pdf, other]

Many-body topological invariants from randomized measurements

Andreas Elben, Jinlong Yu, Guanyu Zhu, Mohammad Hafezi, Frank Pollmann, Peter Zoller, Benoît Vermersch

Subjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el)

The classification of symmetry-protected topological (SPT) phases in one dimension has been recently achieved, and had a fundamental impact in our understanding of quantum phases in condensed matter physics. In this framework, SPT phases can be identified by many-body topological invariants, which are quantized non-local correlators for the many-body wavefunction. While SPT phases can now be realized in interacting synthethic quantum systems, the direct measurement of quantized many-body topological invariants has remained so far elusive. Here, we propose measurement protocols for many-body topological invariants for all types of protecting symmetries of one-dimensional interacting bosonic systems. Our approach relies on randomized measurements implemented with local random unitaries, and can be applied to any spin system with single-site addressability and readout. Our scheme thus provides a versatile toolbox to experimentally classify interacting SPT phases.

Jun 11

arXiv:1906.04235 [pdf, other]

Phase diagram of Rydberg-dressed Fermi gas in two dimensions

Ahmet Keles, Erhai Zhao, Xiaopeng Li

Comments: 6 pages with 2 figures and references

Subjects: Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el); Superconductivity (cond-mat.supr-con)

Rydberg-dressed ultracold Fermi gas is one of the latest quantum many-body systems where the sign, strength, and range of the interaction can be controlled experimentally. The interaction in momentum space has a negative minimum at qc inversely proportional to the characteristic length-scale in real space, the soft-core radius rc . We show theoretically that single-component (spinless) Rydberg-dressed Fermi gas in two dimensions has a rich phase diagram with novel superfluid and density wave orders due to the interplay of the Fermi momentum pF, interaction range rc , and interaction strength u0. For repulsive bare interactions u0 > 0, the dominant instability is f-wave superfluid for pFrc . 2, and density wave for pFrc & 4. The f-wave pairing in a repulsive Fermi gas is reminiscent of, but differs from, the conventional Kohn-Luttinger mechanism. For attractive bare interactions u0 < 0, the leading instability is p-wave pairing with double degeneracy, which points to a px + ipy topological superfluid. The phase diagram is obtained from functional renormalization group with high momentum resolution. It treats all competing many-body instabilities in the particle-particle and particle-hole channels on equal footing beyond leading order perturbation theory and random-phase approximation

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.