Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session P19: Ultracold Atoms: BECs, Interactions and Optical Lattices |
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Sponsoring Units: DAMOP Chair: Adam Kaufman, Harvard University Room: 278-279 |
Wednesday, March 15, 2017 2:30PM - 2:42PM |
P19.00001: Density response function in a non-zero temperature Bose---Einstein Condensates Shohei Watabe Density collective excitation and single particle excitation are interesting in a Bose---Einstein Condensates (BECs). Those are coupled thanks to the BEC and these phonon velocity are common in those two spectrum, which is not seen other system. Furthermore, multi-particle excitations in the density response function have been extensively studied in the context of liquid helium. In this talk, I present the feature of the density response function and spectral function in a non-zero temperature BEC within the random-phase approximation, assuming the ultra-cold quantum gases with a contact interaction not liquid helium including maxon and roton dispersion. [Preview Abstract] |
Wednesday, March 15, 2017 2:42PM - 2:54PM |
P19.00002: Thermodynamics and renormalized quasi-particles in the vicinity of the dilute Bose gas quantum critical point in two dimensions Jan Krieg, Dominik Strassel, Simon Streib, Sebastian Eggert, Peter Kopietz We use the functional renormalization group (FRG) to derive analytical expressions for thermodynamic observables (density, pressure, entropy, and compressibility) as well as for single-particle properties (wavefunction renormalization and effective mass) of interacting bosons in two dimensions as a function of temperature $T$ and chemical potential $\mu$. We focus on the quantum disordered and the quantum critical regime close to the dilute Bose gas quantum critical point. Our approach is based on a truncated vertex expansion of the hierarchy of FRG flow equations and the decoupling of the two-body contact interaction in the particle-particle channel using a suitable Hubbard-Stratonovich transformation. To confirm the validity of our FRG approach, we have also performed quantum Monte Carlo simulations to obtain the magnetization, the susceptibility, and the correlation length of the two-dimensional spin-$1/2$ quantum $XY$ model with coupling $J$ in a regime where its quantum critical behavior is controlled by the dilute Bose gas quantum critical point. We find that our analytical results describe the Monte Carlo data for $\mu \leq 0$ rather accurately up to relatively high temperatures $T \leq 0.1 J$. [Preview Abstract] |
Wednesday, March 15, 2017 2:54PM - 3:06PM |
P19.00003: One Body Density Matrix for Strongly Interacting Spinor Gases in 1D Li Yang, Han Pu We study one dimensional spinor quantum gases from the strong coupling perspective. A family of strong coupling ansatz wavefunctions (physically similar to spin-incoherent Luttinger liquid wavefunctions) can be used to describe the states in this regime. From those wavefunctions, we can interpret the system as a direct product of spin and charge Hilbert spaces, coupled by an effective p-wave interaction. At zero temperature, when the interaction strength approaches infinity, the system fermionizes and the charge degree of freedom is frozen, and the spin degree of freedom is governed by a spin chain Hamiltonian. We found that the one body density matrix of such a strongly interacting 1D spinor gas can be written into a summation of products of charge parts and spin parts. And remarkably, we discover that the charge part is related to the one body density matrix of spinless anyon system via a discrete Fourier transformation. This allows us to obtain a closed form for the one body density matrix of the spinor system. This result allows us to calculate many other important quantities related to the 1D spinor system in a very efficient way, such as the momentum distribution, the Tan relation, and the coupling constants in the spin-chain model. [Preview Abstract] |
Wednesday, March 15, 2017 3:06PM - 3:18PM |
P19.00004: One-dimensional anyons under three-body interactions. Jereson Silva-Valencia, Julian Arcila- Forero, Roberto Franco Anyons are a third class of particles with nontrivial exchange statistics, particles carrying fractional statistics that interpolate between bosons and fermions. In the last years, it has been made some proposals to emulate an anyon gas by confining bosonic atoms in optical lattices [ Nat. Commun. 2, 361 (2011)]. In this work, we studied the ground state of anyons interacting through local three-body terms in one-dimension, motivated by recent experimental and theoretical studies about multi-body interactions in cold atoms setups. We used the density-matrix renormalization group method to find the phase diagram and the von Neumann block entropy to determinate the critical point position. The main quantum phases found are the superfluid and the Mott insulator ones. For the statistical angle $\theta =\pi $/4, the phase diagram shows that the Mott lobes are surrounded by superfluid regions, the Mott lobes increase with the density and the first Mott lobe has two anyons per site. We found that a Mott lobe with one anyon per site, it is possible for larger statistical angles, a fact that it is impossible with bosons. [Preview Abstract] |
Wednesday, March 15, 2017 3:18PM - 3:30PM |
P19.00005: Concept of Contact Matrix in Dilute Quantum Systems He Mingyuan, Zhang Shaoliang, Chan Hon Ming, Zhou Qi The diluteness of ultracold atoms leads to universal thermodynamic relations governed by contact in $s$-wave scattering. In this talk, I will show that the concept of contact can be generalized to an arbitrary partial-wave scattering. Furthermore, to have a complete description of the pairwise correlation in a general dilute quantum system, 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 characterize the coherence of the asymptotic pairwise wavefunction in the angular momentum space. Contact matrix allows physicists to access unexplored connections between short-range correlations and macroscopic quantum phenomena. I will discuss examples of applications of contact matrix in atomic quantum Hall states and superfluids with multiple order parameters. [Preview Abstract] |
Wednesday, March 15, 2017 3:30PM - 3:42PM |
P19.00006: Deep inelastic scattering on ultracold gases Johannes Hofmann, Wilhelm Zwerger I shall discuss the dynamic structure factor of both Bose and Fermi gases with strong short-range interactions, focussing on the deep inelastic regime of large wave vector transfer $q$. Here, the dynamic structure factor is dominated by a resonance at the free-particle energy $\hbar \omega = \varepsilon_{\bf q} = \hbar^2 q^2/2m$ and is described in terms of scaling functions. I will show that the high-momentum structure has a rich scaling behavior characterized by two separate scaling regions: first, for frequencies that differ from the single-particle energy by terms of order ${\cal O}(q)$ (i.e., small deviations compared to the single-particle energy), the dynamic structure factor is described by the impulse approximation (IA) of Hohenberg and Platzman. Second, deviations of order ${\cal O}(q^2)$ (i.e., of the same order or larger than the single-particle energy) are described by the operator product expansion (OPE), with a universal cross-over connecting both regimes. Furthermore, I present an exact expression for the shift of the single-particle peak at large momentum due to interactions, which extends an old result by S. T. Beliaev for the low-density Bose gas to arbitrary values of the scattering length [Preview Abstract] |
Wednesday, March 15, 2017 3:42PM - 3:54PM |
P19.00007: Quantum carpets in a one-dimensional tilted optical lattices Carlos Alberto Parra Murillo, Manuel Humberto Muñoz Arias, Javier Madroñero A unit filling Bose-Hubbard Hamiltonian embedded in a strong Stark field is studied in the off-resonant regime inhibiting single- and many-particle first-order tunneling resonances. We investigate the occurrence of coherent dipole wavelike propagation along an optical lattice by means of an effective Hamiltonian accounting for second-order tunneling processes. It is shown that dipole wave function evolution in the short-time limit is ballistic and that finite-size effects induce dynamical self-interference patterns known as quantum carpets. We also present the effects of the border right after the first reflection, showing that the wave function diffuses normally with the variance changing linearly in time. This work extends the rich physical phenomenology of tilted one-dimensional lattice systems in a scenario of many interacting quantum particles, the so-called many-body Wannier-Stark system. [Preview Abstract] |
Wednesday, March 15, 2017 3:54PM - 4:06PM |
P19.00008: Quantum dimer models emerging in ultracold Mott insulating Bose gases with a large spin Bhuvanesh Sundar, Todd Rutkowski, Michael Lawler, Erich Mueller We propose an experimental protocol to produce quantum dimer models using ultracold bosonic atoms with a large hyperfine spin confined in a deep optical lattice. We propose using an optical Feshbach resonance to engineer spin dependent interactions between bosonic atoms. We show that in the limit of weak lattice tunneling and weak interaction for spin singlets, this system maps to a rich quantum dimer model. For the parameters in our proposal, we find several interesting phases in different lattice geometries: columnar phase on a square lattice, $\sqrt{12}\times\sqrt{12}$ phase on a triangular lattice, and a theoretically unknown phase on a cubic lattice. We give protocols to measure correlations in the ground state using photoassociation and quantum gas microscopy. Experimentally implementing our proposal would allow us to explore models that have a long history in condensed matter physics, and experimentally resolve theoretically unknown phase diagrams in three dimensional lattices. [Preview Abstract] |
Wednesday, March 15, 2017 4:06PM - 4:18PM |
P19.00009: Tunneling frustration induced peculiar supersolid phases in the extended Bose-Hubbard model Lixin He, Shao-Jun Dong, Wenyuan Liu, Xiang-Fa Zhou, Guang-Can Guo, Zheng-Wei Zhou, Yong-Jian Han By using a state of art tensor network state method, we study the ground-state phase diagram of an extended Bose-Hubbard model on square lattice with frustrated next-nearest neighboring tunneling. In the hardcore limit, tunneling frustration stabilizes a peculiar half supersolid (HSS) phase with a SS sublattice and an empty-occupied sublattice away from half filling. A new phase separation regime composes of the HSS and superfluid phases is also identified. In the softcore case, the model show very rich phase diagrams above half filling, including three different types of supersolid phases depending on the interaction parameters. The considered model provides a promising route to realize the stable SS state especially in below half filling region, which can be implemented experimentally with dipolar atoms or molecules. [Preview Abstract] |
Wednesday, March 15, 2017 4:18PM - 4:30PM |
P19.00010: Phonon-mediated repulsion, sharp transitions and (quasi)self-trapping in the extended Peierls-Hubbard model John Sous, Monodeep Chakraborty, Roman Krems, Mona Berciu We study two identical fermions, or two hard-core bosons, in an infinite chain and coupled to phonons by interactions that modulate their hopping as described by the Peierls/Su-Schrieffer- Heeger (SSH) model. We show that exchange of phonons generates effective nearest-neighbor repulsion between particles and also gives rise to interactions that move the pair as a whole. The two-polaron phase diagram exhibits two sharp transitions, leading to light dimers at strong coupling and the flattening of the dimer dispersion at some critical values of the parameters. This dimer (quasi)self-trapping occurs at coupling strengths where single polarons are mobile. This illustrates that, depending on the strength of the phonon-mediated interactions, the coupling to phonons may completely suppress or strongly enhance quantum transport of correlated particles. [Preview Abstract] |
Wednesday, March 15, 2017 4:30PM - 4:42PM |
P19.00011: Artificial gauge-fields in the Bose-Hubbard model on the triangular lattice Shijie Hu, Xue Feng Zhang, Francisco dos Santos, Axel Pelster, Sebastian Eggert Shaking the triangular optical lattice with an extra potential at a resonant frequency can provide different artificial gauge-fields (e.g. complex phases of the tunneling matrix elements between two neighbor lattice sites) along three inequivalent axes. We systematically study the phase diagram of the artificially gauged Bose-Hubbard model on the triangular lattice by using large-scale two-dimensional density-matrix renormalization group (DMRG) method, infinite-DMRG method and also the process-chain algorithm of the strong-coupling expansion. The numerical results self-consistently point out that the artificial gauge-field strongly affect the type of the transitions from the Mott-insulating phase to the superfluid phase. Especially, the transition becomes discontinuous at high-symmetry points because of breaking a topological discrete symmetry. Other properties of criticality are discussed. [Preview Abstract] |
Wednesday, March 15, 2017 4:42PM - 4:54PM |
P19.00012: Laughlin state of hard core bosons on a two-leg ladder Karyn Le Hur, Alexandru Petrescu, Marie Piraud, Ian McCulloch, Guillaume Roux We study hard core bosons on a two leg ladder lattice in uniform magnetic field. At densities which are incommensurate with flux, the ground state is a Meissner state, or a vortex state, depending on the strength of the flux. When the density is commensurate with the flux, analytical arguments predict the existence of a central charge 1 state which is the precursor of the two--dimensional Laughlin state at $\nu \quad =$ 1/2 [1]. We revisit the phase diagram versus density and flux in order to delimit a region where this state is the ground state, by using a combination of bosonization and numerics (density matrix renormalization group and exact diagonalization). We obtain the phase diagram from the properties of local bond current operators and central charge. We use bipartite charge fluctuations to deduce the edge Luttinger liquid describing the edge when the system is in the Laughlin state. The properties studied with local observables are then confirmed by exponential decays in certain correlation functions. Our findings are consistent with a calculation of the many body ground state transverse conductivity in a thin torus geometry for parameters corresponding to the Laughlin state. [1] Alexandru Petrescu and Karyn Le Hur, Phys. Rev. B 91, 054520 (2015) [Preview Abstract] |
Wednesday, March 15, 2017 4:54PM - 5:06PM |
P19.00013: Trapping Centers at the Superfluid–Mott-insulator Criticality: Transition between Charge-quantized States Kun Chen, Yuan Huang, Youjin Deng, Boris Svistunov Under the conditions of superfluid--Mott-insulator criticality in two dimensions, the trapping centers---{\it i.e.,} local potential wells and bumps---are generically characterized by an integer charge corresponding to the number of trapped particles (if positive) or holes (if negative). Varying the strength of the center leads to a transition between two competing ground states with charges differing by $\pm 1$. The hallmark of the transition scenario is a splitting of the number density distortion, $\delta n(r)$, into a half-integer core and a large halo carrying the complementary charge of $\pm 1/2$. The sign of the halo changes across the transition and the radius of the halo, $r_0$, diverges on the approach to the critical strength of the center, $V=V_c$, by the law $r_0 \propto |V-V_c|^{-\tilde{\nu}}$, with $\tilde{\nu}\approx 2.33(5)$. [Preview Abstract] |
Wednesday, March 15, 2017 5:06PM - 5:18PM |
P19.00014: Correlated noise in cold-atom quantum simulation Scott Taylor, Chris Hooley We point out that, when a Hubbard model is simulated by an optical-lattice system with noise in the laser controller, there is generically a correlation between the fluctuations of the hopping amplitude, J, and those of the on-site repulsion, U. We analyse a toy model of such correlated noise. We also show, in a more realistic model, that such correlations lead to a non-trivial ramp-time-independent value of the fidelity in the case of strong noise. [Preview Abstract] |
Wednesday, March 15, 2017 5:18PM - 5:30PM |
P19.00015: Bath Induced Interactions in the Spin-Boson Model in One Dimension Matthew Butcher, Jedediah Pixley, Andriy Nevidomskyy The spin-boson model and its various incarnations have been widely studied for their rich physics and potential for controlling entangled quantum states. In this context, we consider a one-dimensional lattice of Ising spins in a transverse field, coupled to a dissipative bosonic bath with an Ohmic density of states. The separation dependence of two coupled spins has been studied [1], but for more spins the full range of effective interactions have not been included. To study the effects of these induced interactions, we employ a quantum-to-classical mapping [2] to derive the action of the corresponding classical Ising model in two dimensions, which includes time-retarded and long-range spatial interaction terms between all spins. We investigate the correlation functions and critical properties in the classical Monte Carlo simulations, using parallel tempering and efficient update algorithms to mitigate the difficulties of dealing with a highly frustrated spin system. We also investigate the finite size effects.\vspace{3mm} \\ References:\\ {[1]} D. P. S. McCutcheon, A. Nazir, S. Bose, A. J. Fisher, Phys. Rev. B, \textbf{81}, 235321 (2010).\\ {[2]} S. Sachdev, \textit{Quantum Phase Transitions} (Cambridge University Press, Cambridge, England, 1999). [Preview Abstract] |
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