Nov 2013

Nov 25-Nov 29, Zhenyu Zhou | Nov 28 | Nov 27 | Nov 26 | Nov 25 | Nov 18-Nov 22, Li-Jun Lang | Nov 22 | Nov 21 | Nov 20 | Nov 19 | Nov 18 | Nov 25-Nov 29 Zhenyu Zhou | Nov 4-Nov 8, Jinlong Yu | Nov 8 | Nov 7 | Nov 6 | Nov 5 | Nov 4

Nov 25-Nov 29, Zhenyu Zhou

Nov 28
1. arXiv:1311.6925 (cross-list from quant-ph) [pdf, other]
Curved quantum waveguides: Nonadiabatic couplings and gauge theoretical structure
J. Stockhofe, P. Schmelcher
Subjects: Quantum Physics (quant-ph); Quantum Gases (cond-mat.quant-gas)

We investigate the quantum mechanics of a single particle constrained to move along an arbitrary smooth reference curve by a confinement that is allowed to vary along the waveguide. The Schr\"odinger equation is evaluated in the adapted coordinate frame and a transverse mode decomposition is performed, taking into account both curvature and torsion effects and the possibility of a cross-section potential that changes along the curve in an arbitrary way. We discuss the adiabatic structure of the problem, and examine nonadiabatic couplings that arise due to the curved geometry, the varying transverse profile and their interplay. The exact multi-mode matrix Hamiltonian is taken as the natural starting point for few-mode approximations. Such approximative equations are provided, and it is worked out how these recover known results for twisting waveguides and can be applied to other types of waveguide designs. The quantum waveguide Hamiltonian is recast into a form that clearly illustrates how it generalizes the Born-Oppenheimer Hamiltonian encountered in molecular physics. In analogy to the latter, we explore the local gauge structure inherent to the quantum waveguide problem and suggest the usefulness of diabatic states, giving an explicit construction of the adiabatic-to-diabatic basis transformation.

Nov 27
1. arXiv:1311.6634 [pdf, other]
Observation of grand-canonical number statistics in a photon Bose-Einstein condensate
Julian Schmitt, Tobias Damm, David Dung, Frank Vewinger, Jan Klaers, Martin Weitz
Subjects: Quantum Gases (cond-mat.quant-gas)

We report measurements of particle number correlations and fluctuations of a photon Bose-Einstein condensate in a dye microcavity using a Hanbury Brown-Twiss experiment. The photon gas is coupled to a reservoir of molecular excitations, which serve both as heat bath and particle reservoir to realize grand-canonical conditions. For large reservoirs, we observe strong number fluctuations of order of the total particle number extending deep into the condensed phase. Our results demonstrate that Bose-Einstein condensation under grand-canonical ensemble conditions does not imply second-order coherence.

2. arXiv:1311.6708 (cross-list from nlin.PS) [pdf, ps, other]
Non-autonomous bright-dark solitons and Rabi oscillations in multi-component Bose-Einstein condensates
T. Kanna, R. Babu Mareeswaran, F. Tsitoura, H. E. Nistazakis, D. J. Frantzeskakis
Journal-ref: J. Phys. A: Math. Theor. 46 (2013) 475201 (26pp)
Subjects: Pattern Formation and Solitons (nlin.PS); Quantum Gases (cond-mat.quant-gas)

We study the dynamics of non-autonomous bright-dark matter-wave solitons in two- and three- component Bose-Einstein condensates. Our setting includes a time-dependent parabolic potential and scattering length, as well as Rabi coupling of the separate hyperfine states. By means of a similarity transformation, we transform the non-autonomous coupled Gross-Pitaevskii equations into the completely integrable Manakov model with defocusing nonlinearity, and construct the explicit form of the non-autonomous soliton solutions. The propagation characteristics for the one-soliton state, and collision scenarios for multiple soliton states are discussed in detail for two types of time-dependent nonlinearities: a kink-like one and a periodically modulated one, with appropriate time-dependence of the trapping potential. We find that in the two-component condensates the nature of soliton propagation is determined predominantly by the nature of the nonlinearity, as well as the temporal modulation of the harmonic potential; switching in this setting is essentially due to Rabi coupling. We also perform direct numerical simulation of the non-autonomous two-component coupled Gross-Pitaevskii equations to corroborate our analytical predictions. More interestingly, in the case of the three-component condensates, we find that the solitons can lead to collision-induced energy switching (energy-sharing collision), that can be profitably used to control Rabi switching or vice-versa. An interesting possibility of reversal of the nature of the constituent soliton, i.e., bright (dark) into dark (bright) due to Rabi coupling is demonstrated in the three-component setting.

Nov 26
1. arXiv:1311.6177 [pdf, other]
The Raman dressed spin-1 spin-orbit coupled quantum gas
Zhihao Lan, Patrik Ohberg
Subjects: Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph); Quantum Physics (quant-ph)

The recently realized spin-orbit coupled quantum gases (Y.-J Lin {\it et al}., Nature 471, 83-86 (2011); P. Wang {\it et al}., PRL 109, 095301 (2012); L. W. Cheuk {\it et al}., PRL 109, 095302 (2012)) mark a breakthrough in the cold atom community. In these experiments, two hyperfine states are selected from a hyperfine manifold to mimic a pseudospin-1/2 spin-orbit coupled system by the method of Raman dressing, which is applicable to both bosonic and fermionic gases. In this work, we show that the method used in these experiments can be generalized to create any large pseudospin spin-orbit coupled gas if more hyperfine states are coupled equally by the Raman lasers. As an example, we study in detail a quantum gas with three hyperfine states coupled by the Raman lasers, and show when the state-dependent energy shifts of the three states are comparable, triple-degenerate minima will appear at the bottom of the band dispersions, thus realizing a spin-1 spin-orbit coupled quantum gas. A novel feature of this three minima regime is that there can be two different kinds of stripe phases with different wavelengths, which has an interesting connection to the ferromagnetic and polar phases of spin-1 spinor BECs without spin-orbit coupling.

2. arXiv:1311.6289 (cross-list from hep-ph) [pdf, ps, other]
Universal physics of three bosons with isospin
Tetsuo Hyodo, Tetsuo Hatsuda, Yusuke Nishida
Subjects: High Energy Physics - Phenomenology (hep-ph); Quantum Gases (cond-mat.quant-gas); High Energy Physics - Lattice (hep-lat); Nuclear Theory (nucl-th)

We show that there exist two types of universal phenomena for three-boson systems with isospin degrees of freedom. In the isospin symmetric limit, there is only one universal three-boson bound state with the total isospin one, whose binding energy is proportional to that of the two-boson bound state. With large isospin symmetry breaking, the standard Efimov states of three identical bosons appear at low energies. Both phenomena can be realized by three pions with the pion mass appropriately tuned in lattice QCD simulations, or by spin-one bosons in cold atom experiments. Implication to the in-medium softening of multi-pion states is also discussed.

Nov 25

Spin Waves and Dielectric Softening of Polar Molecule Condenstates
Ryan M. Wilson, Brandon M. Peden, Charles W. Clark, Seth T. Rittenhouse
Subjects: Quantum Gases (cond-mat.quant-gas)


We consider an oblate Bose-Einstein condensate of heteronuclear polar molecules in a weak applied electric field. This system supports a rich quasiparticle spectrum that plays a critical role in determining its bulk dielectric properties. In particular, in sufficiently weak fields the system undergoes a polarization wave rotonization, leading to the development of textured electronic structure and a dielectric instability that is characteristic of the onset of a negative static dielectric function.

Nov 18-Nov 22, Li-Jun Lang
Nov 22
1. arXiv:1311.5539 [pdf, other]
Universal symmetry-protected topological invariants for symmetry-protected topological states
Ling-Yan Hung, Xiao-Gang Wen
Subjects: Strongly Correlated Electrons (cond-mat.str-el); High Energy Physics - Theory (hep-th)

Symmetry-protected topological (SPT) states are short-range entangled states with a symmetry G. They belong to a new class of quantum states of matter which are classified by the group cohomology Hd+1(G,R/Z) in d-dimensional space. In this paper, we propose a class of symmetry- protected topological invariants that may allow us to fully characterize SPT states with a symmetry group G (ie allow us to measure the cocycles in Hd+1(G,R/Z) that characterize the SPT states). We give an explicit and detailed construction of symmetry-protected topological invariants for 2+1D SPT states. Such a construction can be directly generalized to other dimensions.

2. arXiv:1311.5393 [pdf, other]
Bose-Einstein Condensation and Many-Body Localization of Rotational Excitations of Polar Molecules
M. P. Kwasigroch, N. R. Cooper
Subjects: Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph); Quantum Physics (quant-ph)
We study theoretically the collective dynamics of rotational excitations of polar molecules loaded into an optical lattice in two dimensions. These excitations behave as hard-core bosons with a relativistic energy dispersion arising from the dipolar coupling between molecules. This has interesting consequences for the collective many-body phases. The rotational excitations can form a Bose-Einstein condensate at non-zero temperature, manifesting itself as a divergent T2 coherence time of the rotational transition even in the presence of inhomogeneous broadening. The dynamical evolution of a dense gas of rotational excitations shows regimes of non-ergodicity, characteristic of many-body localization and localization protected quantum order.



Nov 21
1. arXiv:1311.5174 [pdf, other]
Direct Observation of Fragmentation in a Disordered, Strongly Interacting Fermi Gas
Sebastian Krinner, David Stadler, Jakob Meineke, Jean-Philippe Brantut, Tilman Esslinger
Subjects: Quantum Gases (cond-mat.quant-gas)

Describing the behaviour of strongly interacting particles in the presence of disorder is among the most challenging problems in quantum many-body physics. The controlled setting of cold atom experiments provides a new avenue to address these challenges [1], complementing studies in solid state physics, where a number of puzzling findings have emerged in experiments using superconducting thin films [2,3]. Here we investigate a strongly interacting thin film of an atomic Fermi gas subject to a random potential. We use high-resolution in-situ imaging [4-7] to resolve the atomic density at the length scale of a single impurity, which would require scanning probe techniques in solid state physics [8]. This allows us to directly observe the fragmentation of the density profile and to extract its percolation properties. Transport measurements in a two-terminal configuration indicate that the fragmentation process is accompanied by a breakdown of superfluidity. Our results suggest that percolation of paired atoms is responsible for the loss of superfluidity, and that disorder is able to increase the binding energy of pairs.

2. arXiv:1311.5146 [pdf, other]
Observation of a Strong Atom-Dimer Attraction in a Mass-Imbalanced Fermi-Fermi Mixture
Michael Jag, Matteo Zaccanti, Marko Cetina, Rianne S. Lous, Florian Schreck, Rudolf Grimm, Dmitry S. Petrov, Jesper Levinsen
Subjects: Quantum Gases (cond-mat.quant-gas)
We investigate a mixture of ultracold fermionic 40K atoms and weakly bound 6Li40K dimers on the repulsive side of a heteronuclear atomic Feshbach resonance. By radio-frequency spectroscopy we demonstrate that the normally repulsive atom-dimer interaction is turned into a strong attraction. The phenomenon can be understood as a three-body effect in which two heavy 40K fermions exchange the light 6Li atom, leading to attraction in odd partial-wave channels (mainly p-wave). Our observations show that mass imbalance in a fermionic system can profoundly change the character of interactions as compared to the well-established mass-balanced case.




Nov 20
1. arXiv:1311.4693 [pdf, ps, other]
Hydrodynamic theory of motion of quantized vortex rings in trapped superfluid gases
Lev P. Pitaevskii
Subjects: Quantum Gases (cond-mat.quant-gas)

I study vortex ring oscillations in a superfluid, trapped in an elongated trap, under the conditions of the Local Density Approximation. On the basis of the Hamiltonian formalism I develop a hydrodynamic theory, which is valid for an arbitrary superfluid and depends only on the equation of state. The problem is reduced to an ordinary differential equation for the ring radius. The cases of the dilute BEC and the Fermi gas at unitarity are investigated in detail. Simple analytical equations for the periods of small oscillations are obtained and the equations of non-linear dynamics are solved in quadratures. The results agree with available numerical calculations. Experimental possibilities to check the predictions are discussed.

2. arXiv:1311.4652 [pdf, other]
Direct Detection of Cooper Pair Momentum in Fulde-Ferrell Superconductors
Wei Chen, Ming Gong, R. Shen, D. Y. Xing
Subjects: Superconductivity (cond-mat.supr-con); Mesoscale and Nanoscale Physics (cond-mat.mes-hall)
Finite momentum pairing for Cooper pair in inhomogeneous superconductors represents the most fascinating conceptual extension of the celebrated Bardeen-Cooper-Schrieffer theory of superconductivity. In the past five decades, great endeavors have been paid trying to unveil this novel phase; unfortunately, only indirect evidences related to the possible finite momentum pairing have been reported. In this Letter, we propose an Andreev interferometer based on a branched Y-junction to directly detect the Cooper pair momentum in the Fulde-Ferrell (FF) superconductor, which provides the most convincing evidence for finite momentum pairing. In this device, the subgap conductance is a unique function of the phase difference of the two channels induced by the phase modulation of the FF superconductor without any intervention of other uncontrollable phases during the multiply Andreev scatterings in the Y-junction. This interferometer may have intriguing applications in the identification of the possible finite momentum pairing in non-centrosymmetric superconductors.




Nov 19
1. arXiv:1311.4134 [pdf, other]
Quantum pumping induced by disorder in one dimension
Huaiming Guo
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Strongly Correlated Electrons (cond-mat.str-el)

The topological property in one dimension (1D) is protected by symmetry. Based on a concrete model, we show that since a 1D topological model usually contain two of the three Pauli matrix, the left one automatically become the protecting symmetry. We study the effect of disorder preserving or breaking the symmetry and show the nature of symmetry protecting in the 1D topological phase. Based on the 1D topological model, a stable quantum pumping can be constructed, which is topologically nontrivial and can be characterized by the Chern number. By calculating the instantaneous local current we show that an integer charge is pumped across a periodic chain in a cyclic process. Also on an open chain, an edge state can be transferred to the other edge by the quantum pumping. Furthermore we find that not only the quantum pumping is stable to on-site disorder, but also can be induced by it. These results may be realized experimentally using quasicrystals.

2. arXiv:1311.4113 [pdf, ps, other]
Quantum Anomalous Hall Effect in Magnetically Doped InAs/GaSb Quantum Wells
Qingze Wang, Xin Liu, Hai-Jun Zhang, Nitin Samarth, Shou-Cheng Zhang, Chao-Xing Liu
Subjects: Mesoscale and Nanoscale Physics (cond-mat.mes-hall); Materials Science (cond-mat.mtrl-sci)
The quantum anomalous Hall effect has recently been observed experimentally in thin films of Cr doped (Bi,Sb)2Te3 at a low temperature (∼ 30mK). In this work, we propose realizing the quantum anomalous Hall effect in more conventional diluted magnetic semiconductors with doped InAs/GaSb type II quantum wells. Based on a four band model, we find an enhancement of the Curie temperature of ferromagnetism due to band edge singularities in the inverted regime of InAs/GaSb quantum wells. Below the Curie temperature, the quantum anomalous Hall effect is confirmed by the direct calculation of Hall conductance. The parameter regime for the quantum anomalous Hall phase is identified based on the eight-band Kane model. The high sample quality and strong exchange coupling make magnetically doped InAs/GaSb quantum wells good candidates for realizing the quantum anomalous Hall insulator at a high temperature.


Nov 18
1. arXiv:1311.3820 [pdf, ps, other]
Propagation of collective modes in non-overlapping dipolar Bose-Einstein condensates
A. Gallemi, M. Guilleumas, R. Mayol, M. Pi
Subjects: Quantum Gases (cond-mat.quant-gas)

We investigate long-range effects of the dipolar interaction in Bose-Einstein condensates by solving the time-dependent 3D Gross-Pitaevskii equation. We study the propagation of excitations between non-overlapping condensates when a collective mode is excited in one of the condensates. We obtain the frequency shifts due to the long-range character of the dipolar coupling for the bilayer and also the trilayer system when the dipolar mode is excited in one condensate. The propagation of the monopolar and quadrupolar modes are also investigated. The coupled-pendulum model is proposed to qualitatively explain the long range effects of the dipolar coupling.

2. arXiv:1311.3892 [pdf, other]
Route to observing topological edge modes in ultracold fermions
Junjun Xu, Qiang Gu, Erich J. Mueller
Subjects: Quantum Gases (cond-mat.quant-gas)

We show how to exploit the rich hyperfine structure of fermionic alkali atoms to produce a quasi-1D topological superfluid while avoiding excessive heating from off-resonant scattering. We model interacting fermions where four hyperfine states are coupled by a variety of optical and microwave fields. We calculate the local density of states in a trap, finding regimes with zero energy topological edge modes. Heating rates in this system are significantly suppressed compared to simple Raman-induced spin-orbit coupling approaches.

Nov 25-Nov 29 Zhenyu Zhou

Nov 4-Nov 8, Jinlong Yu

Nov 8
1. arXiv:1311.1783 [pdf, other]
Effective three-body interactions via photon-assisted tunneling in an optical lattice
Andrew J. Daley, Jonathan Simon
We present a simple, experimentally realizable method to make coherent three-body interactions dominate the physics of an ultracold lattice gas. Our scheme employs either lattice modulation or laser-induced tunneling to reduce or turn off two-body interactions in a rotating frame, promoting three-body interactions arising from multi-orbital physics to leading-order processes. This approach provides a route to strongly-correlated phases of lattice gases that are beyond the reach of previously proposed dissipative three-body interactions. In particular, we study the mean-field phase diagram for spinless bosons with three- and two- body interactions, and provide a roadmap to dimer states of varying character in 1D. This new toolset should be immediately applicable in state-of-the-art cold atom experiments.

2. arXiv:1311.1662 (cross-list from cond-mat.mes-hall) [pdf, ps, other]
Photoluminescence of high-density exciton-polariton condensates
Natsuko Ishida, Tim Byrnes, Tomoyuki Horikiri, Franco Nori, Yoshihisa Yamamoto
We examine the photoluminescence of highly-excited exciton-polariton condensates in semiconductor microcavities. Under strong pumping, exciton-polariton condensates have been observed to undergo a lasing transition where strong coupling between the excitons and photons is lost. We discuss an alternative high-density scenario, where the strong coupling is maintained. We find that the photoluminescence smoothly transitions between the lower polariton energy to the cavity photon energy. An intuitive understanding of the change in spectral characteristics is given, as well as differences to the photoluminescence characteristics of the lasing case.

3. arXiv:1311.1604 [pdf, ps, other]
Two-species hardcore bosons on the triangular lattice: a quantum Monte Carlo study
Jian-Ping Lv, Qing-Hu Chen, Youjin Deng
Using worm-type quantum Monte Carlo simulations, we investigate bosonic mixtures on the triangular lattice of two species of bosons, which interact via nearest-neighbour intraspecies (V) and onsite interspecies (U) repulsions. For the case of symmetric hopping amplitude (tA/V=tB/V) and U/V=1, we determine a rich ground-state phase diagram that contains double solid, double superfluid (2SF), supersolid (SS), solid-superfluid (Solid-SF) and counterflow supersolid (CSS) states. The SS, Solid-SF and CSS states exhibit spontaneous symmetry breaking among the three sublattices of the triangular lattice and between the two species, which leads to nonzero crystalline density wave order in each species. We furthermore show that the CSS and the SS states are present for tA/V≠tB/V, and the latter even survives up to tA/V→∞ or tB/V→∞ limit. The effects induced by the variation of U/V and by the imbalance of particle numbers of the two species are also explored.

Nov 7
1. arXiv:1311.1290 [pdf, ps, other]
Magic polarization for optical trapping of atoms without Stark-induced dephasing
Huidong Kim, Hyok Sang Han, D. Cho
We demonstrate that the differential ac-Stark shift of a ground-state hyperfine transition in an optical trap can be eliminated by using properly polarized trapping light. We use the vector polarizability of an alkali-metal atom to produce a polarization-dependent ac-Stark shift that resembles a Zeeman shift. We study a transition from the |2S1/2,F=2,mF=-2> to the |2S1/2,F=1,mF=-1> state of 7Li to observe 0.59+-0.02 Hz linewidth with interrogation time of 2 s and 0.82+-0.06 s coherence time of a superposition state. Implications of the narrow linewidth and the long coherence time for precision spectroscopy and quantum information processing using atoms in an optical lattice are discussed.

Nov 6
1. arXiv:1311.1011 [pdf, ps, other]
A surface-patterned chip as a strong source of ultra-cold atoms for quantum technologies
C. C. Nshii, M. Vangeleyn, J. P. Cotter, P. F. Griffin, E. A. Hinds, C. N. Ironside, P. See, A. G. Sinclair, E. Riis, A. S. Arnold
Laser cooled atoms are central to modern precision measurements. They are also increasingly important as an enabling technology for experimental cavity quantum electrodynamics, quantum information processing and matter wave interferometry. Although significant progress has been made in miniaturising atomic metrological devices, these are limited in accuracy by their use of hot atomic ensembles and buffer gases. Advances have also been made in producing portable apparatus that benefit from the advantages of atoms in the microKelvin regime. However, simplifying atomic cooling and loading using microfabrication technology has proved difficult. In this letter we address this problem, realising an atom chip that enables the integration of laser cooling and trapping into a compact apparatus. Our source delivers ten thousand times more atoms than previous magneto-optical traps with microfabricated optics and, for the first time, can reach sub-Doppler temperatures. Moreover, the same chip design offers a simple way to form stable optical lattices. These features, combined with the simplicity of fabrication and the ease of operation, make these new traps a key advance in the development of cold-atom technology for high-accuracy, portable measurement devices.

2. arXiv:1311.1118 [pdf, ps, other]
Quench Dynamics of the Anisotropic Heisenberg Model
Wenshuo Liu, Natan Andrei
We develop an analytic approach for the study of the quench dynamics of the anisotropic Heisenberg model (XXZ model) on the infinite line. We present the exact time-dependent wavefunctions after a quench in an integral form for any initial state and for any anisotropy Δ by means of a generalized Yudson contour representation. We calculate the evolution of several observables from two particular initial states: starting with a local N\`eel state we calculate the time evolution of the antiferromagnetic order parameter--staggered magnetization; starting with a state with consecutive flipped spins we calculate the propagation of magnons and bound state excitations, and the induced spin currents. We also show how the "string" solution of Bethe Ansatz equations emerge naturally from the contour approach. We confront our results with experiments and numerical methods where possible.

3. arXiv:1311.1028 [pdf, ps, other]
Breakdown of scale invariance in a quasi-two-dimensional Bose gas due to the presence of the third dimension
Karina Merloti (LPL), Romain Dubessy (LPL), Laurent Longchambon (LPL), Maxim Olshanii (LPL), Hélène Perrin (LPL)
In this Letter, we describe how the presence of the third "hidden" dimension may break the scale invariance in a two-dimensional Bose gas in a pancake trap. From the two-dimensional perspective, the possibility of a weak spilling of the atomic density beyond the ground state of the confinement alters the two-dimensional chemical potential; in turn, this correction no longer supports scale invariance. We compare experimental data with numerical and analytic perturbative results and find a fair agreement.

4. arXiv:1310.5580 [pdf, ps, other]
How many is different? Answer from ideal Bose gas
Jeong-Hyuck Park
How many H2O molecules are needed to form water? While the precise answer is not known, it is clear that the answer should be a finite number rather than infinity. We revisit with care the ideal Bose gas confined in a cubic box which is discussed in most statistical physics textbooks. We show that the isobar of the ideal gas zigzags on the temperature-volume plane featuring a `boiling-like' discrete phase transition, provided the number of particles is equal to or greater than a particular value: 7616. This demonstrates for the first time how a finite system can feature a mathematical singularity and realize the notion of `Emergence', without resorting to the thermodynamic limit.

5. arXiv:1311.0876 [pdf, other]
Two-dimensional superfluidity in driven systems requires strong anisotropy
Ehud Altman, John Toner, Lukas M. Sieberer, Sebastian Diehl, Leiming Chen
We show that driven two-dimensional Bose systems cannot exhibit algebraic superfluid order unless the underlying microscopic system is strongly anisotropic. Our result implies, in particular, that recent apparent evidence for Bose condensation of exciton-polaritons in semiconductor quantum wells must be an intermediate scale crossover phenomenon, while the true long distance correlations fall off exponentially. We obtain these results through a mapping of the long-wavelength condensate dynamics onto the anisotropic Kardar-Parisi-Zhang equation.

Nov 5
1. arXiv:1311.0769 [pdf, ps, other]
Bosonic thermoelectric transport and breakdown of universality
A. Rancon, Cheng Chin, K. Levin
In this paper we compare Bose transport in normal phase atomic gases with its counterpart in Fermi gases, illustrating the non-universality of two dimensional bosonic transport associated with different dissipation mechanisms. Near the superfluid transition temperature T_c, a striking similarity between the fermionic and bosonic transport emerges because super-conducting(fluid) fluctuation transport for Fermi gases is dominated by the bosonic, Cooper pair component. As in fluctuation theory, one finds that the Seebeck coefficient changes sign at T_c and the Lorenz number approaches zero atT_c. Our findings appear semi-quantitatively consistent with recent Bose gas experiments.

2. arXiv:1311.0441 [pdf, ps, other]
Magneto--optical matter wave Bragg diffraction
Yueyang Zhai, Peng Zhang, Xuzong Chen, Guangjiong Dong, Xiaoji Zhou
We have performed a principle-proof-experiment of a magneto-optical diffraction (MOD) technique that requires no energy level splitting by homogeneous magnetic field and a circularly polarized optical lattice, avoiding system errors in an interferometer based on the MOD. The principle for this new MOD is that asynchronized switching of quadrupole trap and Ioffe trap in a quadrupole-Ioffe-configuration trap can generate a residual magnetic force to drive a Bose-Einstein condensate (BEC) to move. We have observed asymmetric atomic diffraction resulting from the asymmetric distribution of the Bloch eigenstates involved in the diffraction process when the condensate is driven by such a force, and matter-wave self-imaging due to coherent population oscillation of the dominantly occupied Bloch eigenstates. We have classified the mechanisms that lead to symmetric or asymmetric diffraction, and found that our experiment presents a magnetic alternative to a moving optical lattice, with a great potential to achieve a very large momentum transfer (>110ℏk) to a BEC using well-developed magnetic trapping techniques.

3. arXiv:1311.0543 [pdf, other]
Optical Lattice Emulators: Bose and Fermi Hubbard Models
Eric Duchon, Yen Lee Loh, Nandini Trivedi
This chapter is a pedagogical review of the Hubbard model for bosons with repulsion and for fermions with attraction and repulsion primarily using two methods, one chosen for its simplicity and insights (mean field theory) and the other chosen for its accuracy and reliability (quantum Monte Marlo methods). From a comparison of the two methods we glean valuable information into the effects of fluctuations that dominate quantum phase transitions. The chapter includes an in-depth comparison with experiments. We conclude with a discussion of future developments where the technical methods expounded on here, mean field theory and quantum Monte Carlo, could be useful.

4. arXiv:1311.0429 (cross-list from quant-ph) [pdf, other]
Evaporative cooling of reactive polar molecules confined in a two-dimensional geometry
Bihui Zhu, Goulven Quéméner, Ana M. Rey, Murray J. Holland
Recent experimental developments in the loading of ultracold KRb molecules into quasi-two-dimensional traps, combined with the ability to tune the ratio between elastic and loss (inelastic/reactive) collisions through application of an external electric field, are opening the door to achieving efficient evaporative cooling of reactive polar molecules. In this paper, we use Monte Carlo simulations and semianalytic models to study theoretically the experimental parameter regimes in which evaporative cooling is feasible under current trapping conditions. We investigate the effect of the anisotropic character of dipole-dipole collisions and reduced dimensionality on evaporative cooling. We also present an analysis of the experimentally relevant anti-evaporation effects that are induced by chemical reactions that take place when more than one axial vibrational state is populated.

Nov 4
1. arXiv:1311.0250 [pdf, other]
Design of a millimetre-scale magnetic surface trap for cold atoms
Dimitris Trypogeorgos, Stephen D. Albright, Daniel Beesley, Christopher J. Foot
We study a novel millimetre-scale magnetic trap for ultracold atoms, in which the current carrying conductors can be situated outside the vacuum region, a few mm away from the atoms. This design generates a magnetic field gradient in excess of \SI{1000}{G/cm} at a distance of \SI{2}{mm} from the conductors. We perform electromagnetic and thermo-mechanical characterisation using Finite Element Methods (FEM). The predicted behaviour has been verified by electrical and thermal measurements on a prototype, but has not been implemented on an apparatus with cold atoms. Operating this trap at the highest gradient allows for rapid evaporative cooling comparable to that achieved by atom chips.

2. arXiv:1311.0073 [pdf, other]
The effect of optical lattice heating on the momentum distribution of a 1D Bose gas
Jean-Félix Riou, Laura A. Zundel, Aaron Reinhard, David S. Weiss
We theoretically study how excitations due to spontaneous emission and trap fluctuations combine with elastic collisions to change the momentum distribution of a trapped non-degenerate one-dimensional (1D) Bose gas. Using calculated collisional relaxation rates, we first present a semi-analytical model for the momentum distribution evolution to get insight into the main processes responsible for the system dynamics. We then present a Monte-Carlo simulation that includes features that cannot be handled analytically, and compare its results to experimental data. These calculations provide a baseline for how integrable 1D Bose gases evolve due to heating processes in the absence of diffractive collisions that might thermalize the gases.

3. arXiv:1311.0179 [pdf, other]
Inhomogeneous phases in one-dimensional mass- and spin-imbalanced Fermi gases
Dietrich Roscher, Jens Braun, Joaquín E. Drut
We compute the phase diagram of strongly interacting fermions in one dimension at finite temperature, with mass and spin imbalance. By including the possibility of the existence of a spatially inhomogeneous ground state, we find regions where spatially varying superfluid phases are favored over homogeneous phases. We obtain estimates for critical values of the temperature, mass and spin imbalance, above which these phases disappear. Finally, we show that an intriguing relation exists between the general structure of the phase diagram and the binding energies of the underlying two-body bound-state problem.