Aug+2017

= Aug 1-Aug 10 Biao Huang, Aug 11-Aug 20 Haiyuan Zou, Aug 21-Aug 30 Zehan Li =

= Aug 18 = [|arXiv:1708.05014] (cross-list from quant-ph) [ [|pdf], [|other] ] Boundary time crystals [|F. Iemini], [|A. Russomanno] , [|J. Keeling] , [|M. Schirò] , [|M. Dalmonte] , [|R. Fazio]   Comments: 5 + 6 pages, 4 + 5 figures  Subjects: Quantum Physics (quant-ph) ; Other Condensed Matter (cond-mat.other); Statistical Mechanics (cond-mat.stat-mech) In this work we introduce {\it boundary time-crystals}. Here {\it continuous} time-translation symmetry breaking occurs at the boundary (or generically in a macroscopic portion) of a many-body quantum system. After introducing their definition and properties, we analyse in details a solvable model. We provide examples of other systems where boundary time crystalline phases can occur. The existence of the boundary time crystals is intimately connected to the emergence of time-periodic steady state in the thermodynamic limit of a many-body open quantum system. Connection to quantum synchronisation will be also discussed.

= Aug 17 = [|arXiv:1708.04626] [ [|pdf], [|other] ] Fermionic spinon theory of square lattice spin liquids near the Néel state [|Alex Thomson], [|Subir Sachdev]   Comments: 32 pages, 5 figures, 12 tables  Subjects: Strongly Correlated Electrons (cond-mat.str-el) Quantum fluctuations of the N\'eel state of the square lattice antiferromagnet are usually described by a ℂℙ 1  theory of bosonic spinons coupled to a U(1) gauge field, and with a global SU(2) spin rotation symmetry. Such a theory also has a confining phase with valence bond solid (VBS) order, and upon including spin-singlet charge 2 Higgs fields, deconfined phases with ℤ 2  topological order possibly intertwined with discrete broken global symmetries. We present dual theories of the same phases starting from a mean-field theory of fermionic spinons moving in π  -flux in each square lattice plaquette. Fluctuations about this π  -flux state are described by 2+1 dimensional quantum chromodynamics (QCD  3  ) with a SU(2) gauge group and  N f = 2  flavors of massless Dirac fermions. It has recently been argued by Wang et al. ( [|arXiv:1703.02426] ) that this QCD 3  theory describes the N\'eel-VBS quantum phase transition. We introduce adjoint Higgs fields in QCD 3 , and obtain fermionic dual descriptions of the phases with  ℤ 2  topological order obtained earlier using the bosonic  ℂℙ 1  theory. We also present a fermionic spinon derivation of the monopole Berry phases in the U(1) gauge theory of the VBS state. The global phase diagram of these phases contains multi-critical points, and our results imply new boson-fermion dualities between critical gauge theories of these points.

= Aug 15 = [|arXiv:1708.03810] [ [|pdf], [|other] ] Localized magnetic moments with tunable spin exchange in a gas of ultracold fermions [|Luis Riegger], [|Nelson Darkwah Oppong] , [|Moritz Höfer] , [|Diogo Rio Fernandes] , [|Immanuel Bloch] , [|Simon Fölling]   Subjects: Quantum Gases (cond-mat.quant-gas) We report on the experimental realization of a state-dependent lattice for a two-orbital fermionic quantum gas with strong interorbital spin exchange. In our state-dependent lattice, the ground and metastable excited electronic states of 173  Yb take the roles of itinerant and localized magnetic moments, respectively, with a spin-exchange interaction analog to that in the well-known Kondo Hamiltonian. The exchange interaction arises from the difference in the on-site interaction of the nuclear spin singlet- and triplet configurations. In addition, we find that the resulting spin coupling can be tuned resonantly by varying the on-site confinement. We attribute this to a resonant coupling to center-of-mass excited bound states of the spin-singlet scattering channel.

= Aug 14 = [|arXiv:1708.03348] [ [|pdf], [|other] ] Realization of "Time Crystal" Lagrangians and Emergent Sisyphus Dynamics [|Alfred D. Shapere], [|Frank Wilczek]   Comments: 5 pages, 5 figures  Subjects: Statistical Mechanics (cond-mat.stat-mech) ; Pattern Formation and Solitons (nlin.PS); Quantum Physics (quant-ph) We demonstrate how non-convex "time crystal" Lagrangians arise in the effective description of conventional, realizable physical systems. Such embeddings allow for the resolution of dynamical singularities that arise in the reduced description. Sisyphus dynamics, featuring intervals of forward motion interrupted by quick resets, is a generic consequence. Near the would-be singularity of the time crystal, we find striking microstructure.

= Aug 11 = [|arXiv:1708.02980] [ [|pdf], [|other] ] Chiral Liquid Phase of Simple Quantum Magnets [|Zhentao Wang], [|Adrian E. Feiguin] , [|Wei Zhu] , [|Oleg A. Starykh] , [|Andrey V. Chubukov] , [|Cristian D. Batista]   Comments: 19 pages, 14 figures  Subjects: Strongly Correlated Electrons (cond-mat.str-el) We study a T = 0  quantum phase transition between a quantum paramagnetic state and a magnetically ordered state for a spin  S = 1  XXZ Heisenberg antiferromagnet on a two-dimensional triangular lattice. The transition is induced by an easy plane single-ion anisotropy D. At the mean-field level, the system undergoes a direct transition at a critical D = D c  between a paramagnetic state at  D > D c  and an ordered state with broken  U ( 1 )  symmetry at  D < D c. We show that beyond mean-field the phase diagram is very different and includes an intermediate, partially ordered chiral liquid phase. Specifically, we find that inside the paramagnetic phase the Ising ( J z  ) component of the Heisenberg exchange binds magnons into a two-particle bound state with zero total momentum and spin. This bound state condenses at D > D c , before single particle excitations become unstable, and gives rise to a chiral liquid phase, which spontaneously breaks spatial inversion symmetry, but leaves the spin-rotational  U ( 1 )  and time-reversal symmetries intact. This chiral liquid phase is characterized by a finite vector chirality without long range dipolar magnetic order. In our analytical treatment, the chiral phase appears for arbitrary small J z  because the magnon-magnon attraction becomes singular near the single-magnon condensation transition. This phase exists in a finite range of D  and transforms into the magnetically ordered state at some  D < D c. We corroborate our analytic treatment with numerical density matrix renormalization group calculations.

Aug 8 [|arXiv:1708.02404] [[|pdf], [|ps], [|other]] Entanglement prethermalization in the Tomonaga-Luttinger model [|Eriko Kaminishi], [|Takashi Mori], [|Tatsuhiko N Ikeda], [|Masahito Ueda] Comments: 9 pages  Subjects: Statistical Mechanics (cond-mat.stat-mech) ; Quantum Gases (cond-mat.quant-gas) Prethermalization refers to the relaxation to a quasi-stationary state before reaching thermal equilibrium. Recently, it is found that not only local conserved quantities but also entanglement plays a key role in a special type of prethermalization, called entanglement prethermalization. Here, we show that in the Tomonaga-Luttinger model the entanglement prethermalization can also be explained by the conventional prethermalization of two independent subsystems without entanglement. Moreover, it is argued that prethermalization in the Tomonaga-Luttinger model is essentially different from entanglement prethermalization in the Lieb-Liniger model because of the different types of energy degeneracies.

Aug 7 [|arXiv:1708.02229] [[|pdf], [|other]] Observation of metastability in an open quantum system with long-range interactions [|Lorenz Hruby], [|Nishant Dogra], [|Manuele Landini], [|Tobias Donner], [|Tilman Esslinger] Comments: 7 + 5 pages, 5 + 4 figures  Subjects: Quantum Gases (cond-mat.quant-gas) We study metastability of a Mott-insulator and a charge density wave in an extended Bose-Hubbard model with global-range interactions. The model is realized by loading a degenerate 87  Rb Bose gas into a three-dimensional optical lattice. The global-range interactions are mediated by photons dispersively scattered from a lattice beam - off the quantum gas - into an optical cavity mode. Initializing the system in a Mott insulating state, we rapidly increase the strength of global-range interactions to different final values. We observe that the system falls into either of two possible final states, which is one signature of metastability. This is achieved by monitoring the photon flux leaking from the cavity, which is determined by the atomic density modulation. We associate a state possessing a small density modulation (low photon flux) with a Mott insulator, and a state possessing a large density modulation (high photon flux) with a charge density wave. In additional experiments, we slowly increase the strength of global-range interactions and subsequently decrease it again, and observe a hysteresis loop between the two states, which is a second signature of metastability. Furthermore, based on an analysis of an extended Bose-Hubbard model in the zero tunneling limit, we confirm that the observed metastability can arise from strong and competing short- and global-range interactions. The transition between the two observed states requires a local redistribution of a large number of particles. The analysis of the observed temporal dynamics of the transition suggests that a collective tunneling process is triggered.

[|arXiv:1708.02112] [[|pdf], [|other]] Synthetic dimensions in ultracold molecules: quantum strings and membranes [|Bhuvanesh Sundar], [|Bryce Gadway], [|Kaden R. A. Hazzard] Comments: 10 pages, 6 figures  Subjects: Quantum Gases (cond-mat.quant-gas) We show that rotational states of ultracold molecules can be used as synthetic dimensions extending to many -- potentially hundreds of -- synthetic lattice sites. Microwaves coupling rotational states drive synthetic inter-site tunnelings with fully controllable magnitudes and phases. When molecules are frozen in a periodic real space array with uniform synthetic tunnelings, the system undergoes a spontaneous dimensional reduction beyond a critical value of the dipole interaction. In this state, the system collapses to a narrow strip in the synthetic direction, resulting in a quantum string (for a 1D chain of molecules) or a membrane (for a 2D array). At large interactions, an emergent strongly interacting condensate lives on the string or membrane. In a 2D array of molecules, we also find evidence of a metastable non-Abelian Ising anyon phase. We show that all these phases can be detected using local measurements of rotational state populations.