Jun 2016
May 30-Jun 3 Bo Liu, Jun 6-Jun 10 Biao Huang, Jun 13-Jun 17 Haiyuan Zou, Jun 20-Jun 24 Ahmet Kel, Jun 27-July 1 Max
Jun 17 arXiv:1606.05176 [pdf, other] Contact matrix in dilute quantum systems Shao-Liang Zhang, Mingyuan He, Qi Zhou Comments: typos corrected, relevant references added Subjects: Quantum Gases (cond-mat.quant-gas) Contact has been well established as an important quantity to govern dilute quantum systems, in which the pairwise correlation at short distance traces a broad range of thermodynamic properties. So far, studies have been focusing on contact in individual angular momentum channels. Here, we point out that, to have a complete description of the pairwise correlation in a general dilute quantum systems, contact should be defined as a matrix. Whereas the diagonal terms of such matrix include contact of all partial wave scatterings, the off-diagonal terms, which elude previous studies in the literature, characterise the coherence of the asymptotic pairwise wavefunction in the angular momentum space and determine important thermodynamic quantities including the momentum distribution. Contact matrix allows physicists to access unexplored connections between short-range correlations and macroscopic quantum phenomena. As an example, we show the direct connection between contact matrix and order parameters of a superfluid with mixed partial waves. Jun 16 arXiv:1606.04755 [pdf, other] Quantized Vortices and Four-Component Superfluidity of Semiconductor Excitons Romain Anankine, Mussie Beian, Suzanne Dang, Mathieu Alloing, Edmond Cambril, Kamel Merghem, Carmen Gomez Carbonell, Aristide Lemaitre, Francois Dubin Massive bosonic particles realise a rich variety of collective quantum phenomena where their underlying fermionic structure is hardly observed. For example, Bose-Einstein condensation of atomic gases is quantitatively understood by neglecting the atoms fermionic nature. Semiconductor excitons, i.e. Coulomb-bound electron-hole pairs, constitute a class of composite bosons which contrasts with this behaviour. Indeed, Combescot and co-workers have predicted that the excitons underlying fermionic structure governs Bose-Einstein condensation. It leads to a dominantly dark condensate where fermion exchanges between excitons control the occupation of accessible spin states, namely the two pairs of optically bright and dark states. Here we report the long-awaited fingerprints for this dark state of quantum-matter searched since the 1960's. We use time and spatially resolved interferometry to demonstrate quantized vortices which form spontaneously in a superfluid largely made of dark excitons, below a critical temperature of the order of 1 Kelvin. The quantum coherence shown by the superfluid bright-part signals unambiguously that fermion exchanges are responsible for a complex four-component quantum phase transition, in a regime where the deviation from the ideal bosonic case remains small. Thus, our observations mark a new frontier of research where fermion exchanges between composite bosons will unveil hidden facets of quantum-matter. Jun 15 arXiv:1606.04267 [pdf, other] Cluster Bose Metals Tao Ying, Marcello Dalmonte, Peter Zoller, Guido Pupillo Comments: 4 pages, 3 figures Subjects: Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el) Quantum phases of matter are usually characterised by broken symmetries. Identifying physical mechanisms and microscopic Hamiltonians that elude this paradigm is one of the key present challenges in many-body physics. Here, we use quantum Monte-Carlo simulations to show that a Bose metal phase, breaking no symmetries, is realized in simple Hubbard models for bosonic particles on a square lattice complemented by soft-shoulder interactions. The enabling mechanism is provided by cluster formation in the corresponding classical tiling problem. The Bose metal is separated from a superfluid glass by a continuous transition showing non-classical exponents and winding numbers consistent with deconfined quantum criticality. The identification of such cluster mechanism paves the way to the realization of exotic quantum liquids in both natural and synthetic quantum matter that harbors cluster formation. Jun 9, Thursday arXiv:1606.02454 Creating and probing the Sachdev-Ye-Kitaev model with ultracold gases: Towards experimental studies of quantum gravity Ippei Danshita, Masanori Hanada, Masaki Tezuka (Submitted on 8 Jun 2016) We suggest that the holographic principle, combined with recent technological advances in atomic, molecular, and optical physics, can lead to experimental studies of quantum gravity. As a specific example, we consider the Sachdev-Ye-Kitaev (SYK) model, which consists of spin-polarized fermions with an all-to-all random two-body hopping and has been conjectured to be dual to a certain quantum gravitational system. We propose that the SYK model can be engineered by confining ultracold fermionic atoms into optical lattices and coupling two atoms with molecular states via photo-association lasers. Achieving low-temperature states of the SYK model is interpreted as a realization of a stringy black hole, provided that the holographic duality is true. We also show how to measure out-of-time-order correlation functions of the SYK model, which allow for identifying the maximally chaotic property of the black hole. Jun 7, Tuesday arXiv:1606.01717 Observation of two-species vortex lattices in a mixture of mass-imbalance Bose and Fermi superfluids Xing-Can Yao, Hao-Ze Chen, Yu-Ping Wu, Xiang-Pei Liu, Xiao-Qiong Wang, Xiao Jiang, Youjin Deng, Yu-Ao Chen, Jian-Wei Pan (Submitted on 6 Jun 2016) The superfluid mixture of interacting Bose and Fermi species is a remarkable many-body quantum system. Dilute degenerate atomic gases, especially for two species of distinct masses, are excellent candidates for exploring fundamental features of superfluid mixture. However, producing a mass-imbalance Bose-Fermi superfluid mixture, providing an unambiguous visual proof of two-species superfluidity and probing inter-species interaction effects remain challenging. Here, we report the realization of a two-species superfluid of lithium-6 and potassium-41. By rotating the dilute gases, we observe the simultaneous existence of vortex lattices in both species, and thus present a definitive visual evidence for the simultaneous superfluidity of the two species. Pronounced effects of the inter-species interaction are demonstrated through a series of precision measurements on the formation and decay of two-species vortices. Our system provides a new platform for studying novel macroscopic quantum phenomena in vortex matter of interacting species. Jun 3 1. arXiv:1606.00824 [pdf, other] Self-bound dipolar droplet: a localized matter-wave in free space D. Baillie, R. M. Wilson, R. N. Bisset, P. B. Blakie We demonstrate that a dipolar condensate can be prepared into a three-dimensional wavepacket that remains localized when released in free-space. Such self-bound states arise from the interplay of the two-body interactions and quantum fluctuations. We develop a phase diagram for the parameter regimes where these self-bound states are stable, examine their properties, and demonstrate how they can be produced in current experiments. 2. arXiv:1606.00562 (cross-list from quant-ph) [pdf, other] Engineering two-photon states via interaction between Rydberg atoms during the light storage J. Ruseckas, I. A. Yu, G. Juzeliūnas We propose a new method to create two-photon states in a controllable way using interaction between the Rydberg atoms during the storage and retrieval of slow light. A distinctive feature of the suggested procedure is that the slow light is stored into a superposition of two atomic coherences under conditions of electromagnetically induced transparency (EIT). Interaction between the atoms during the storage period creates entangled pairs of atoms in a superposition state that is orthogonal to the initially stored state. Restoring the slow light from this new atomic state one can produce a two photon state with a second-order correlation function determined by the atom-atom interaction and the storage time. Therefore the measurement of the restored light allows one to probe the atom-atom coupling by optical means with a sensitivity that can be increased by extending the storage time. As a realization of this idea we consider a many-body Ramsey-type technique which involves pi/2 pulses creating a superposition of Rydberg states at the beginning and the end of the storage period. In that case the regenerated light is due to the resonance dipole-dipole interaction between the atoms in the Rydberg states. Jun 2 1. arXiv:1606.00015 [pdf, other] Creating topological interfaces and detecting chiral edge modes in a 2D optical lattice N. Goldman, G. Jotzu, M. Messer, F. Görg, R. Desbuquois, T. Esslinge We propose and analyze a general scheme to create chiral topological edge modes within the bulk of two-dimensional engineered quantum systems. Our method is based on the implementation of topological interfaces, designed within the bulk of the system, where topologically-protected edge modes localize and freely propagate in a unidirectional manner. This scheme is illustrated through an optical-lattice realization of the Haldane model for cold atoms, where an additional spatially-varying lattice potential induces distinct topological phases in separated regions of space. We present two realistic experimental configurations, which lead to linear and radial-symmetric topological interfaces, which both allows one to significantly reduce the effects of external confinement on topological edge properties. Furthermore, the versatility of our method opens the possibility of tuning the position, the localization length and the chirality of the edge modes, through simple adjustments of the lattice potentials. In order to demonstrate the unique detectability offered by engineered interfaces, we numerically investigate the time-evolution of wave packets, indicating how topological transport unambiguously manifests itself within the lattice. Finally, we analyze the effects of disorder on the dynamics of chiral and non-chiral states present in the system. Interestingly, engineered disorder is shown to provide a powerful tool for the detection of topological edge modes in cold-atom setups. Jun 1 1. arXiv:1605.09760 [pdf, other] Long-range Ordering of Topological Excitations in a Two-Dimensional Superfluid Far From Equilibrium Hayder Salman, Davide Maestrini We study the relaxation of a 2D ultracold Bose-gas from a nonequilibrium initial state containing vortex excitations in experimentally realizable square and rectangular traps. We show that the subsystem of vortex gas excitations results in the spontaneous emergence of a coherent superfluid flow with a non-zero coarse-grained vorticity field. The streamfunction of this emergent quasi-classical 2D flow is governed by a Boltzmann-Poisson equation. This equation reveals that maximum entropy states of a neutral vortex gas that describe the spectral condensation of energy can be classified into types of flow depending on whether or not the flow spontaneously acquires angular momentum. Numerical simulations of a neutral point vortex model and a Bose gas governed by the 2D Gross-Pitaevskii equation in a square reveal that a large scale monopole flow field with net angular momentum emerges that is consistent with predictions of the Boltzmann-Poisson equation. The results allow us to characterise the spectral energy condensate in a 2D quantum fluid that bears striking similarity with similar flows observed in experiments of 2D classical turbulence. By deforming the square into a rectangular region, the resulting maximum entropy state switches to a dipolar flow field with zero net angular momentum.
