Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session Z16: Bosons in Optical Lattices II |
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Sponsoring Units: DAMOP Chair: Trey Porto, National Institute of Standards and Technology, Gaithersburg Room: 317 |
Friday, March 20, 2009 11:15AM - 11:27AM |
Z16.00001: Optical lattice-based addressing and control of long-lived neutral-atom qubits Nathan Lundblad, Trey Porto, Ian Spielman, Radu Chicireanu, William Phillips Many proposed quantum computational platforms are driven by competing needs: isolating the quantum system from the environment to prevent decoherence, and easily and accurately controlling the system with external fields. For example, neutral-atom optical-lattice architectures provide environmental isolation through the use of states that are robust against fluctuating external fields, yet external fields are inherently useful for qubit addressing. Here we demonstrate a technique to address qubits formed from a pair of field-insensitive states by transferring the qubit into a {\em different} pair of field-insensitive states. A spatially inhomogeneous external field allows the addressing of particular ``marked" elements of a qubit register, leaving unmarked qubits unaffected, despite the presence of crosstalk or leakage of the addressing field. We demonstrate this technique in an ensemble of $^{87}$Rb atoms and show that we can robustly perform single-qubit rotations on qubits located at addressed lattice sites. This precise coherent control is an important step forward for lattice-based neutral-atom quantum computation, and is applicable to state transfer and qubit isolation in other architectures using field-insensitive qubits. [Preview Abstract] |
Friday, March 20, 2009 11:27AM - 11:39AM |
Z16.00002: ABSTRACT WITHDRAWN |
Friday, March 20, 2009 11:39AM - 11:51AM |
Z16.00003: Vortices near the Mott phase of a trapped Bose-Einstein condensate Daniel Goldbaum, Erich Mueller We present a theoretical study of vortices within a harmonically trapped Bose-Einstein condensate in a rotating optical lattice. We find that proximity to the Mott insulating state dramatically affects the vortex structures. To illustrate we give examples in which the vortices: (i) all sit at a fixed distance from the center of the trap, forming a ring, or (ii) coalesce at the center of the trap, forming a giant vortex. We model the imaging of these structures by calculating time-of-flight column densities. As in the absence of the optical lattice, the vortices are much more easily observed in a time-of-flight image than \emph{in-situ}. \\ \\ D.~S. Goldbaum and E.~J. Mueller, \emph{Vortices near the Mott phase of a trapped Bose-Einstein condensate}, arXiv:0808.1548. [Preview Abstract] |
Friday, March 20, 2009 11:51AM - 12:03PM |
Z16.00004: Boson Hubbard model with weakly coupled fermions Sumanta Tewari, Roman Lutchyn, Sankar Das Sarma Using an imaginary-time path integral approach, we develop the perturbation theory suited to the boson Hubbard model, and apply it to calculate the effects of a dilute gas of spin- polarized fermions weakly interacting with the bosons. The full theory captures both the static and the dynamic effects of the fermions on the generic superfluid-insulator phase diagram. We find that, in a homogenous system described by a single-band boson Hubbard Hamiltonian, the intrinsic perturbative effect of the fermions is to suppress the Mott insulating lobes and enhance the superfluid phase. [Preview Abstract] |
Friday, March 20, 2009 12:03PM - 12:15PM |
Z16.00005: Boson Hubbard model with weakly coupled fermions: Effects of higher bands and shrinking of the superfluid phase Sankar Das Sarma, Roman Lutchyn, Sumanta Tewari We study Boson Hubbard model with weakly coupled fermions and take into account the effects of the higher boson Bloch bands. For attractive couplings between the bosons and the fermions, mixing of the higer bands results in an effective enhancement of the boson on-site repulsion. The overall shift of the boson Hubbard phase diagram due to the presence of the fermions is thus determined by two competing effects: an effective fermion- mediated interaction between the constituent bosons (which favors the superfluid phase), and the renormalization of the boson-boson interaction due to the virtual boson transitions to the higher Bloch bands (which favors the Mott insulating phase). We find that the latter is typically dominant for the cold-atom experiments, which is consistent with the observed loss of the superfluid coherence in recent experiments. [Preview Abstract] |
Friday, March 20, 2009 12:15PM - 12:27PM |
Z16.00006: Scattering Properties of Bose-Hubbard Hamiltonians with Two and Three Sites Moritz Hiller, Stefan Hunn, Tsampikos Kottos, Doron Cohen, Andreas Buchleitner We consider a probe particle in a tight binding geometry with two leads and a central site that is coupled to a Bose-Hubbard system consisting of two or three wells (dimer/trimer). In the case of the dimer we find that the resonance widths undergo a sequence of bifurcations resulting from the complexity of the underlying classical phase space structure. For the trimer we show that the statistical properties of the scattering matrix are well described by the random matrix theory predictions for chaotic scattering. The origin of this agreement is due to the fact that inelastic scattering from a chaotic system (trimer) is formally equivalent to elastic scattering in a waveguide that has a chaotic mode space. [Preview Abstract] |
Friday, March 20, 2009 12:27PM - 12:39PM |
Z16.00007: Quantum fluctuations and self-organization of a BEC in a multimode optical cavity Sarang Gopalakrishnan, Benjamin Lev, Paul Goldbart An ultracold bosonic gas, trapped in an optical cavity, crystallizes at either the even or the odd antinodes of the cavity mode, if the cavity is pumped transversely with a strong laser beam. Spontaneous symmetry breaking between even and odd antinodes is favored because atoms spaced one wavelength apart coherently emit the light absorbed from the laser, populate the cavity with photons, and thus trap themselves in attractive optical potential wells. For a single-mode cavity, the transition to a crystalline state has been observed [1] and is well described by mean-field theory [2]. However, in multimode cavities, either confocal or concentric, fluctuations are enhanced and change the character of the transition, resulting in a quantal version of the Brazovskii transition in layering systems. We derive a field-theoretic description of the atom- cavity system near the transition, and describe how fluctuations and defects imprint themselves on the correlations of the light leaking out of the cavity. [1] A.T. Black et al, Phys. Rev. Lett. 91, 203001 (2003). [2] J.K. Asboth et al, Phys. Rev. A 72, 053417 (2005). [Preview Abstract] |
Friday, March 20, 2009 12:39PM - 12:51PM |
Z16.00008: Role of Spatial Inhomogeneity in the Experimental Determination of the Two Dimensional Bose-Hubbard Model Critical Point Khan W. Mahmud, Valery G. Rousseau, Marcos Rigol, George G. Batrouni, Richard T. Scalettar Recent experiments at NIST on confined Rb atoms in two dimensions, combined with high precision Quantum Monte Carlo (QMC) values for the homogeneous Bose-Hubbard model critical point, represented important progress toward testing the concept of optical lattice emulator. The experimentally determined critical coupling for the superfluid-Mott transition is in quite good agreement with the QMC results $(U/t)_c = 16.74$ for the homogeneous case. We present an analysis of these results which takes into account the spatial inhomogeneity arising from the confining potential. We perform a detailed QMC calculation of the density profile, local density fluctuations, and condensate fraction along the trajectory followed experimentally. We demonstrate that for the number of atoms, optical lattice depth, curvature of the confining potential, and temperature in the NIST experiment, the critical value for the formation of Mott domains is rather close to that of the homogeneous system. [Preview Abstract] |
Friday, March 20, 2009 12:51PM - 1:03PM |
Z16.00009: Superfluid to Mott-insulator transition of hardcore bosons in a superlattice Itay Hen, Marcos Rigol We present results of analytical and numerical studies of the superfluid to Mott-insulator transition of hardcore bosons in a superlattice potential in arbitrary dimensions. In this study, we use mean-field plus spin-wave corrections and the stochastic series expansion (SSE) algorithm to compute various properties of the system, such as the ground-state energy, the condensate fraction, the superfluid density, and the compressibility. We will show that in some cases the spin-wave approximation is in remarkable agreement with the exact numerical results. [Preview Abstract] |
Friday, March 20, 2009 1:03PM - 1:15PM |
Z16.00010: The single-atom box: bosonic staircase and effects of parity Christoph Bruder, D.V. Averin, T. Bergeman, P.R. Hosur We have developed [1] a theory of a Josephson junction formed by two tunnel-coupled Bose-Einstein condensates in a double-well potential in the regime of strong atom-atom interaction for an arbitrary total number $N$ of bosons in the condensates. The tunnel resonances in the junction are shown to be periodically spaced by the interaction energy, forming a single-atom staircase sensitive to the parity of $N$ even for large $N$. One of the manifestations of the staircase structure is the periodic modulation with the bias energy of the visibility of the interference pattern in lattices of junctions. A different, e.g. fermionic, additional particle in the junction leads to non-trivial modifications of the staircase, that can be experimentally observed in the visibility of the interference pattern. [1] D.V. Averin, T. Bergeman, P.R. Hosur, and C. Bruder, Phys. Rev. A {\bf 78}, 031601(R) (2008). [Preview Abstract] |
Friday, March 20, 2009 1:15PM - 1:27PM |
Z16.00011: Spin field effect transistors with ultracold atoms G. Juzeliunas, J. Ruseckas, Charles W. Clark, J.Y. Vaishnav We propose a method of constructing cold atom analogs of the spintronic device known as the Datta-Das transistor (DDT), which despite its seminal conceptual role in spintronics, has never been successfully realized with electrons. We propose two alternative schemes for an atomic DDT, both of which are based on the experimental setup for tripod stimulated Raman adiabatic passage. Both setups involve atomic beams incident on a series of laser fields mimicking the relativistic spin orbit coupling for electrons that is the operating mechanism of the DDT. [Preview Abstract] |
Friday, March 20, 2009 1:27PM - 1:39PM |
Z16.00012: Vortex quantum dynamics of two dimensional lattice bosons Netanel Lindner, Assa Auerbach, Daniel P. Arovas We study hard core lattice bosons in a magnetic field near half filling\footnote{See: arXiv:0810.2604}. The strong periodic potential scatters the vortices by units of reciprocal lattice momenta, enhancing their mobility and modifying their effective Magnus field. The bare vortex hopping rate on the dual lattice is extracted by exact diagonalizations of square clusters. We deduce quantum melting of the vortex lattice above vortex density of $6.5\times10^{-3}$ per lattice site. The Hall conductivity, which reflects the vortex Magnus dynamics, reverses sign abruptly at half filling. The characteristic temperature scale of the Hall conductivity vanishes at the transition point. We prove that at half filling, each vortex carries a spin half quantum number (`v-spin'). Experimental implications of these results are relevant for diverse systems of current interest, e.g. cold atoms on rotating optical lattices, arrays of Josephson junctions and underdoped cuprate superconductors. [Preview Abstract] |
Friday, March 20, 2009 1:39PM - 1:51PM |
Z16.00013: Mapping out the finite temperature phase diagram of the Bose Hubbard model Qi Zhou, Yasuyuki Kato, Naoki Kawashima, Nandini Trivedi We propose a method to experimentally map out the phase diagram of Bose-Hubbard Model at finite temperatures solely based on the density distribution of trapped bosonic atoms in optical lattices. Based on Quantum Monte Carlo simulations in a trap with 10$^{5}$ bosons, we show that the phase boundary between the superfluid and normal state is directly located from kinks in the compressibility, which are extracted from the density profile itself. The temperature of bosons in the lattice is obtained from the density profile at the edge. Our method uses general aspects of critical fluctuations at a phase transition and can be extended to other systems, even when exact numerical simulations are not available. [Preview Abstract] |
Friday, March 20, 2009 1:51PM - 2:03PM |
Z16.00014: Distributions of entropy and superfluid density of trapped bosons in optical lattices Nandini Trivedi, Yasuyuki Kato, Qi Zhou, Naoki Kawashima Based on a large scale quantum Monte Carlo simulations of the Bose Hubbard model using the worm algorithm[1], we calculate the inhomogeneous distribution of entropy and superfluid density of trapped bosons in optical lattices. We show that most of the entropy is concentrated in the conducting shells. As the lattice is ramped up under adiabatic conditions, we show that the temperature increases and the superfluid regions in the trap can vanish. However, by opening up the trap at fixed lattice height, the system effectively cools, the entropy gets redistributed in the trap and superfluid regions reemerge. [1] Sharp Peaks in the Momentum Distribution of Bosons in Optical Lattices in Normal State Yasuyuki Kato, Qi Zhou, Naoki Kawashima and Nandini Trivedi Nature Physics, 4, 617 (2008) [Preview Abstract] |
Friday, March 20, 2009 2:03PM - 2:15PM |
Z16.00015: Observing the Quantum Spin Hall Effect with Ultracold Atoms J.Y. Vaishnav, Tudor D. Stanescu, Charles W. Clark, Victor Galitski The quantum spin Hall (QSH) state is a topologically nontrivial state of matter proposed to exist in certain 2-D systems with spin-orbit coupling. While the electronic states of a QSH insulator are gapped in the bulk, a QSH insulator is characterized by gapless edge states of different spins which counterpropagate at a given edge; the spin is correlated with the direction of propagation. Recent proposals \footnote{T. D. Stanescu, C. Zhang, V. Galitski, {\it Physical Review Letters} {\bf 99}, 110403 (2007), J. Y. Vaishnav, Charles W. Clark, {\it Physical Review Letters} {\bf 100}, 153002 (2008).} suggest that synthetic spin-orbit couplings can be created for cold atoms moving in spatially varying light fields. Here, we identify an optical lattice setup which generates an effective QSH effect for cold, multilevel atoms. We also discuss methods for experimental detection of the atomic QSH effect. [Preview Abstract] |
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