May2012

flat =May 28 - Jun 1, Bin Wang=

Interaction-induced localization of fermionic mobile impurities in a Larkin-Ovchinnikov superfluid
===[|Jian Li], [|Jin An], [|C. S. Ting]=== We theoretically investigate the interplay between the fermionic mobile impurity atoms and a Larkin-Ovchinnikov (LO) superfluid in a two dimensional optical lattice. We find that the impurity atoms get localized and can form pairs when the interaction between the impurity atoms and the LO superfluid is strong enough. These features are due to the phenomena of self-localization whose underlying mechanism is found to be revealed by an effective model. The impurity atoms with finite concentrations can drive the transition from a two-dimensional-checkerboard-like LO state to a quasi-one-dimensional-stripe-like one. Experimental preparations to realize these features are also discussed.

[|Andrew P. Snyder], [|Theja N. De Silva]
We study long-time spin diffusion of harmonically trapped lattice fermions in one dimension. Combining thermodynamic Bethe ansatz approach and local density approximation, we calculate spin current and spin diffusion coefficient driven by the population imbalance. We find spin current is driven by susceptibility effects rather than typical diffusion where magnetization would transport from regions of high magnetization to low. As expected, spin transport is zero through insulating regions and are only present in the metallic regions. In the weak coupling limit, the local spin diffusion coefficient shows maxima at all the insulating regions. Further, we estimate damping rate of diffusion modes in the weak coupling limit within the lower metallic portion of the cloud. The predicted spin current pattern can be probed via currently available experimental techniques.

===3. [|arXiv:1205.6999] (cross-list from quant-ph) [[|pdf], [|ps], [|other]] ===

Dynamics of one-dimensional tight-binding models with arbitrary time-dependent external homogeneous fields
===[|W. H. Hu], [|L. Jin], [|Z. Song]=== The exact propagators of two one-dimensional systems with time-dependent external fields are presented by following the path-integral method. It is shown that the Bloch acceleration theorem can be generalized to the impulse-momentum theorem in quantum version. We demonstrate that an evolved Gaussian wave packet always keeps its shape in an arbitrary time-dependent homogeneous driven field. Moreover, that stopping and accelerating of a wave packet can be achieved by the pulsed field in a diabatic way.

[|Xing-Hai Zhang], [|Su-Peng Kou]
In this paper, we studied a generalized Bose-Hubbard model on a checkerboard lattice with topologically nontrivial flat-band. We used mean-field method to decouple the model Hamiltonian and obtained phase diagram by Landau theory of second-order phase transition. We further calculate the energy gap and the dispersion of quasi-particle or quasi-hole in Mott insulator state and found that in strong interaction limit the quasi-particles or the quasi-holes also have flat bands.

Sum rules, dipole oscillation and spin polarizability of a spin-orbit coupled quantum gas
===[|Yun Li], [|Giovanni Martone], [|Sandro Stringari]=== Using a sum rule approach we investigate the dipole oscillation of a spin-orbit coupled Bose-Einstein condensate confined in a harmonic trap. The crucial role played by the spin polarizability of the gas is pointed out. We show that the lowest dipole frequency exhibits a characteristic jump at the transition between the stripe and spin-polarized phase. Near the second order transition between the spin-polarized and the single minimum phase the lowest frequency is vanishingly small for large condensates, reflecting the divergent behavior of the spin polarizability. We compare our results with recent experimental measurements as well as with the predictions of effective mass approximation.

Atomic Quantum Simulation of Dynamical Gauge Fields coupled to Fermionic Matter: From String Breaking to Evolution after a Quench
===[|D. Banerjee], [|M. Dalmonte], [|M. Müller], [|E. Rico], [|P. Stebler], [|U.-J. Wiese], [|P. Zoller]=== Using a Fermi-Bose mixture of ultra-cold atoms in an optical lattice, we construct a quantum simulator for a U(1) gauge theory coupled to fermionic matter. The construction is based on quantum links which realize continuous gauge symmetry with discrete quantum variables. At low energies, quantum link models with staggered fermions emerge from a Hubbard-type model which can be quantum simulated. This allows us to investigate string breaking as well as the real-time evolution after a quench in gauge theories, which are inaccessible to classical simulation methods.

[|Yajiang Hao], [|Shu Chen]
We investigate the dynamical properties of anyons confined in one-dimensional optical lattice combined with a weak harmonic trap using the exact numerical method based on a generalized Jordan-Wigner transformation. The density profiles, momentum distribution, occupation distribution and occupations of the lowest natural orbital are obtained for different statistical parameters. The density profiles of anyons display the same behaviors irrespective of statistical parameter in the full evolving period. While the behaviors dependent on statistical property are shown in the momentum distributions and occupations of natural orbitals.

Dzyaloshinskii-Moriya Interaction and Spiral Order in Spin-orbit Coupled Optical Lattices
===[|Ming Gong], [|Yinyin Qian], [|V. W. Scarola], [|Chuanwei Zhang]=== We show that the recent experimental realization of spin-orbit coupling in ultracold atomic gases can be used to study different types of spiral order and resulting multiferroic effects. Spin-orbit coupling in optical lattices can give rise to the Dzyaloshinskii-Moriya (DM) spin interaction which is essential for spin spiral order. We derive an effective spin model in the deep Mott insulator region at half filling, and demonstrate that the DM interaction in optical lattices can be made extremely strong with realistic experimental parameters. The rich phase diagrams of the effective spin model for fermion and bosons are obtained via classical Monte Carlo simulations.

Dressed, noise- or disorder- resilient optical lattices
===[|Hannes Pichler], [|Johannes Schachenmayer], [|Jonathan Simon], [|Peter Zoller], [|Andrew J. Daley]=== External noise is inherent in any quantum system, and can have especially strong effects for systems exhibiting sensitive many-body phenomena. We show how a dressed lattice scheme can provide control over certain types of noise for atomic quantum gases in the lowest band of an optical lattice, removing the effects of lattice amplitude noise to first order for particular choices of the dressing field parameters. We investigate the non-equilibrium many-body dynamics for bosons and fermions induced by noise away from this parameter regime, and also show how the same technique can be used to reduce spatial disorder in projected lattice potentials.

[|David Snoke]
The similarities and differences between polariton condensation in microcavities and standard lasing in a semiconductor cavity structure are reviewed. The recent experiments on "photon condensation" are also reviewed.

Topological flat band models with arbitrary Chern numbers
===[|Shuo Yang], [|Zheng-Cheng Gu], [|Kai Sun], [|S. Das Sarma]=== We report the theoretical discovery of a systematic scheme to produce topological flat bands (TFBs) with arbitrary Chern numbers. We find that generically a high Chern number TFB model can be constructed by considering multi-layer Chern number C=1 TFB models with enhanced translational symmetry. A series of models are presented as examples, including a two-band model on a triangular lattice with a Chern number C=3 and an $N$-band square lattice model with $C=N$ for an arbitrary integer $N$. In all these models, the flatness ratio for the TFBs is larger than 30 and increases with increasing Chern number. In the presence of appropriate inter-particle interactions, these models are likely to lead to the formation of novel Abelian and Non-Abelian fractional Chern insulators.

= May 21 - May 25, Johannes Schachenmayer = = = = May 22 =

Superfluid behaviour of a two-dimensional Bose gas [|Rémi Desbuquois], [|Lauriane Chomaz] , [|Tarik Yefsah] , [|Julian Léonard] , [|Jérôme Beugnon] , [|Christof Weitenberg] , [|Jean Dalibard] wo-dimensional (2D) systems play a special role in many-body physics. Because of thermal fluctuations, they cannot undergo a conventional phase transition associated to the breaking of a continuous symmetry. Nevertheless they may exhibit a phase transition to a state with quasi-long range order via the Berezinskii-Kosterlitz-Thouless (BKT) mechanism. A paradigm example is the 2D Bose fluid, such as a liquid helium film, which cannot Bose-condense at non-zero temperature although it becomes superfluid above a critical phase space density. Ultracold atomic gases constitute versatile systems in which the 2D quasi-long range coherence and the microscopic nature of the BKT transition were recently explored. However, a direct observation of superfluidity in terms of frictionless flow is still missing for these systems. Here we probe the superfluidity of a 2D trapped Bose gas with a moving obstacle formed by a micron-sized laser beam. We find a dramatic variation of the response of the fluid, depending on its degree of degeneracy at the obstacle location. In particular we do not observe any significant heating in the central, highly degenerate region if the velocity of the obstacle is below a critical value.
 * 1. [|arXiv:1205.4536] [ [|pdf], [|other] ]  **

Creation of ultracold Sr2 molecules in the electronic ground state [|Simon Stellmer], [|Benjamin Pasquiou] , [|Rudolf Grimm] , [|Florian Schreck] We report on the creation of ultracold 84Sr2 molecules in the electronic ground state. The molecules are formed from atom pairs on sites of an optical lattice using stimulated Raman adiabatic passage (STIRAP). We achieve a transfer efficiency of 30% and obtain 4x10^4 molecules with full control over the external and internal quantum state. STIRAP is performed near the narrow 1S0-3P1 intercombination transition, using a vibrational level of the 0u potential as intermediate state. In preparation of our molecule association scheme, we have determined the binding energies of the last vibrational levels of the 0u, 1u excited-state, and the 1\Sigma_g^+ ground-state potentials. Our work overcomes the previous limitation of STIRAP schemes to systems with Feshbach resonances, thereby establishing a route that is applicable to many systems beyond bi-alkalis.
 * 2. [|arXiv:1205.4505] [ [|pdf], [|other] ]  **

Stationary States of Trapped Spin-Orbit-Coupled Bose-Einstein Condensates [|Emmi Ruokokoski], [|Jukka Huhtamäki] , [|Mikko Möttönen] We investigate the stationary states of spin-1 Bose-Einstein condensates in the presence of Rashba-Dresselhaus-type spin-orbit coupling. Previously this coupling has been predicted to generate exotic ground-state structures. We study numerically the energies of various stationary states as functions of the spin-orbit coupling strength and map the ground states of the condensates. Our results indicate that for strong spin-orbit coupling, the ground state is a square vortex lattice, irrespective of the value of the spin-spin coupling. For weak spin-orbit coupling, the lowest-energy state may host a single vortex. Furthermore, starting from the homogeneous approximation, we analytically derive constraints that explain why certain stationary states do not emerge as ground states. Importantly, we show that the distinct stationary states can be observed experimentally by standard time-of-flight spin-independent absorption imaging.
 * 3. [|arXiv:1205.4601] [ [|pdf], [|ps] , [|other] ]  **

= May 21 =

Dynamical arrest of ultracold lattice fermions [|Bernd Schmidt], [|M. Reza Bakhtiari] , [|Irakli Titvinidze] , [|Ulrich Schneider] , [|Michiel Snoek] , [|Walter Hofstetter] We theoretically investigate the thermodynamics of an interacting inhomogeneous two-component Fermi gas in an optical lattice. Motivated by a recent experiment by L. Hackerm\"uller et al., Science, 327, 1621 (2010), we study the effect of the interplay between thermodynamics and strong correlations on the size of the fermionic cloud. We use dynamical mean-field theory to compute the cloud size, which in the experiment shows an anomalous expansion behavior upon increasing attractive interaction. We confirm this qualitative effect but, assuming adiabaticity, we find quantitative agreement only for weak interactions. For strong interactions we observe significant non-equilibrium effects which we attribute to a dynamical arrest of the particles due to increasing correlations.
 * 1. [|arXiv:1205.4031] [ [|pdf], [|ps] , [|other] ]  **

**2. [|arXiv:1205.4121] [ [|pdf], [|other] ] ** Penrose-Onsager Criterion Validation in a One-Dimensional Polariton Condensate [|F. Manni], [|K. G. Lagoudakis] , [|R. André] , [|M. Wouters] , [|B. Deveaud] We perform quantum tomography on one-dimensional polariton condensates, spontaneously occurring in linear disorder valleys in a CdTe planar microcavity sample. By the use of optical interferometric techniques, we determine the first-order coherence function and the amplitude and phase of the order parameter of the condensate, providing a full reconstruction of the single particle density matrix for the polariton system. The experimental data are used as input to theoretically test the consistency of Penrose-Onsager criterion for Bose-Einstein condensation in the framework of nonequilibrium polariton condensates. The results confirm the pertinence and validity of the criterion for a non equilibrium condensed gas.

**3. [|arXiv:1205.4026] [ [|pdf], [|other] ] ** Mott criticality and pseudogap in Bose-Fermi mixturesWe study the Mott transition of a mixed Bose-Fermi system of ultracold atoms in an optical lattice, where the number of (spinless) fermions and bosons adds up to one atom per lattice, n_F+n_B=1. For weak interactions, a Fermi surface coexists with a Bose-Einstein condensate while for strong interaction the system is incompressible but still characterized by a Fermi surface of composite fermions. At the critical point, the spectral function of the fermions, A(k,w), exhibits a pseudo-gapped behavior, rising as |w| at the Fermi momentum, while in the Mott phase it is fully gapped. Taking into account the interaction between the critical modes leads at very low temperatures either to p-wave pairing or the transition is driven weakly first order. The same mechanism should also be important in antiferromagnetic metals with a small Fermi surface.

**4. [|arXiv:1205.4027] [ [|pdf], [|other] ] ** Quantum charge glasses of itinerant fermions with cavity-mediated long-range interactions [|Markus Mueller], [|Philipp Strack] , [|Subir Sachdev] We study models of itinerant spinless fermions with random long-range interactions. We motivate such models from descriptions of fermionic atoms in multi-mode optical cavities. The solution of an infinite-range model yields a metallic phase which has glassy charge dynamics, and a localized glass phase with suppressed density of states at low energies. We compare these phases to the conventional disordered Fermi liquid, and the insulating electron glass of semiconductors. Prospects for the realization of such glassy phases in cold atom systems are discussed.

= May 14 - May 18, Saubhik Sarkar =

= May 18 =

NONE

= May 17 =

Noisy quantum phase transitions: an intuitive approach [|Emanuele G. Dalla Torre], [|Eugene Demler] , [|Thierry Giamarchi] , [|Ehud Altman] Equilibrium thermal noise is known to destroy any quantum phase transition. What are the effects of non-equilibrium noise? In two recent papers we have considered the specific case of a resistively-shunted Josephson junction driven by $1/f$ charge noise. At equilibrium, this system undergoes a sharp quantum phase transition at a critical value of the shunt resistance. By applying a real-time renormalization group (RG) approach, we found that the noise has three main effects: It shifts the phase transition, renormalizes the resistance, and generates an effective temperature. In this paper we explain how to understand these effects using simpler arguments, based on Kirchhoff laws and time-dependent perturbation theory. We also show how these effects modify physical observables and especially the current-voltage characteristic of the junction. In the appendix we describe two possible realizations of the model with ultracold atoms confined to one dimension.
 * 1. [|arXiv:1205.3496] [ [|pdf], [|other] ]  **

**2. [|arXiv:1205.3511] [ [|pdf], [|other] ] ** Second Josephson excitations beyond mean field as a toy model for thermal pressure: exact quantum dynamics and the quantum phase model [|M. P. Strzys], [|J. R. Anglin] A simple four-mode Bose-Hubbard model with intrinsic time scale separation can be considered as a paradigm for mesoscopic quantum systems in thermal contact. In our previous work we showed that in addition to coherent particle exchange, a novel slow collective excitation can be identified by a series of Holstein-Primakoff transformations. This resonant energy exchange mode is not predicted by linear Bogoliubov theory, and its frequency is sensitive to interactions among Bogoliubov quasi-particles; it may be referred to as a second Josephson oscillation, in analogy to the second sound mode of liquid Helium II. In this paper we will explore this system beyond the Gross-Pitaevskii mean field regime. We directly compare the classical mean field dynamics to the exact full quantum many-particle dynamics and show good agreement over a large range of the system parameters. The second Josephson frequency becomes imaginary for stronger interactions, however, indicating dynamical instability of the symmetric state. By means of a generalized quantum phase model for the full four-mode system, we then show that, in this regime, high-energy Bogoliubov quasiparticles tend to accumulate in one pair of sites, while the actual particles preferentially occupy the opposite pair. We interpret this as a simple model for thermal pressure.

Strong-coupling dynamics of Bose-Einstein condensate in a double-well trap [|V. O. Nesterenko], [|A. N. Novikov] , [|E. Suraud] Dynamics of the repulsive Bose-Einstein condensate (BEC) in a double-well trap is explored within the 3D time-dependent Gross-Pitaevskii equation. The model avoids numerous common approximations (two-mode treatment, time-space factorization, fixed values of the chemical potential and barrier penetrability, etc) and thus provides a realistic description of BEC dynamics, including both weak-coupling (sub-barrier) and strong-coupling (above-barrier) regimes and their crossover. The strong coupling regime is achieved by increasing the number $N$ of BEC atoms and thus the chemical potential. The evolution with $N$ of Josephson oscillations (JO) and Macroscopic Quantum Self-Trapping (MQST) is examined and the crucial impact of the BEC interaction is demonstrated. At weak coupling, the calculations well reproduce the JO/MQST experimental data. At strong coupling, with a significant overlap of the left and right BECs, we observe a remarkable persistence of the Josephson-like dynamics: the JO and MQST converge to a high-frequency JO-like mode where both population imbalance and phase difference oscillate around the zero averages. The results open new avenues for BEC interferometry.
 * 3. [|arXiv:1205.3687] [ [|pdf], [|ps] , [|other] ]  **

= May 16 =

**1. [|arXiv:1205.3483] [ [|pdf], [|other] ] ** Spin-Injection Spectroscopy of a Spin-Orbit Coupled Fermi Gas [|Lawrence W. Cheuk], [|Ariel T. Sommer] , [|Zoran Hadzibabic] , [|Tarik Yefsah] , [|Waseem S. Bakr] , [|Martin W. Zwierlein] The coupling of the spin of electrons to their motional state lies at the heart of recently discovered topological phases of matter. Here we create and detect spin-orbit coupling in an atomic Fermi gas, a highly controllable form of quantum degenerate matter. We reveal the spin-orbit gap via spin-injection spectroscopy, which characterizes the energy-momentum dispersion and spin composition of the quantum states. For energies within the spin-orbit gap, the system acts as a spin diode. To fully inhibit transport, we open an additional spin gap, thereby creating a spin-orbit coupled lattice whose spinful band structure we probe. In the presence of s-wave interactions, such systems should display induced p-wave pairing, topological superfluidity, and Majorana edge states.

**2. [|arXiv:1205.3221] [ [|pdf], [|ps] , [|other] ] ** Degeneracies in trapped two-component Fermi gases [|K. M. Daily], [|D. Rakshit] , [|D. Blume] We report on previously unobserved inter-system degeneracies in two-component equal-mass Fermi gases with interspecies zero-range interactions under isotropic harmonic confinement. Over the past 10 years, two-component Fermi gases consisting of $n_1$ spin-up and $n_2$ spin-down atoms with interspecies zero-range interactions have become a paradigm for modeling condensed matter systems, nuclear matter and neutron matter. We show that the eigen energies of the $(n_1+1,n_2-1)$ system are degenerate with the eigen energies of the $(n_1,n_2)$ system for any s-wave scattering length $a_s$, including infinitely large, positive and negative $a_s$. The existence of the inter-system degeneracies is demonstrated explicitly for few-body systems with $n_1+n_2=4, 5$ and 6. The degeneracies and associated symmetries are explained within a group theoretical framework.

**3. [|arXiv:1205.3303] [ [|pdf], [|ps] , [|other] ] ** Quantum relaxation and finite size effects in the XY chain in a transverse field after global quenches [|B. Blass], [|H. Rieger] , [|F. Iglói] We consider global quenches in the quantum XY chain in a transverse field and study the nonequilibrium relaxation of the magnetization and the correlation function as well as the entanglement entropy in finite systems. For quenches in the ordered phase, the exact results are well described by a semiclassical theory (SCT) in terms of ballistically moving quasiparticles. In the thermodynamic limit the SCT is exact for the entanglement entropy and its modified version following the method of Calabrese, Essler and Fagotti: <span style="background-color: #ffffff; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px; text-decoration: none;">[|arXiv:1204.3911] <span style="background-color: #ffffff; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;"> is exact for the magnetization and the correlation function, too. The stationary correlation function is shown to be described by a generalized Gibbs ensemble.

= May 15 = 1. [|arXiv:1205.3116] [ [|pdf], [|ps] , [|other] ] Magnetic phases of bosons with synthetic spin-orbit coupling in optical lattices [|Zi Cai], [|Xiangfa Zhou] , [|Congjun Wu] <span style="background-color: #ffffff; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;">We investigate magnetic properties in the superfluid and Mott-insulating states of two-component bosons with spin-orbit (SO) coupling in 2D square optical lattices. The spin-independent hopping integral $t$ and SO coupled one $\lambda $are fitted from band structure calculations in the continuum, which exhibit oscillations as increasing SO coupling strength. The magnetic superexchange model is derived in the Mott-insulating state with one-particle per-site, characterized by the Dzyaloshinsky-Moriya (DM) interaction. In the limit of $|\lambda|\ll |t|$, we find a spin spiral Mott state whose pitch value is the same as that in the incommensurate superfluid state, while in the opposite limit $|t| \ll |\lambda|$, the ground state exhibits with a $2\times 2$ in-plane spin pattern.

2. [|arXiv:1205.2813] [ [|pdf], [|other] ] Dipolar Bose-Einstein condensate in a ring or in a shell [|S. K. Adhikari] <span style="background-color: #ffffff; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;">We study properties of a trapped dipolar Bose-Einstein condensate (BEC) in a circular ring or a spherical shell using the mean-?eld Gross-Pitaevskii equation. In the case of the ring-shaped trap we consider different orientations of the ring with respect to the polarization direction of the dipoles. In the presence of long-range anisotropic dipolar and short-range contact interactions, the anisotropic density distribution of the dipolar BEC in both traps is discussed in detail. The stability condition of the dipolar BEC in both traps is illustrated in phase plot of dipolar and contact interactions. We also study and discuss the properties of a vortex dipolar BEC in these traps.

<span style="background-color: #ffffff; display: block; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;"> 3. [|arXiv:1205.2700] [ [|pdf], [|other] ] Spectral functions of the Higgs mode near two-dimensional quantum critical points [|Daniel Podolsky], [|Subir Sachdev] <span style="background-color: #ffffff; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;">We study the Higgs excitation in the Goldstone phase of the relativistic O(N) model in two spatial dimensions at zero temperature. The response functions of the order parameter, and its magnitude-squared, become universal functions of frequency in the vicinity of the quantum critical point described by the Wilson-Fisher fixed point, and we compute them to next-to-leading order in 1/N. The Higgs particle has an infrared singular decay to gapless Goldstone excitations, and its response functions are characterized by a pole in the lower-half of the complex frequency plane. The pole acquires a non-zero real part only at next-to-leading order in 1/N, demonstrating that the Higgs excitation has an oscillatory component even in the scaling limit. Both the real and imaginary parts of the pole position vanish with the correlation length exponent \nu upon approaching the critical point. We present evidence that the spectral density of the O(N)-invariant amplitude-squared of the order parameter has a peak at a non-zero frequency in the scaling limit. We connect our results to recent experimental studies of the superfluid-insulator quantum phase transition of ultracold bosonic atoms in optical lattices.

<span style="background-color: #ffffff; display: block; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;"> 4. [|arXiv:1205.2967] (cross-list from cond-mat.str-el) [ [|pdf], [|ps] , [|other] ] Quantum quenches in one-dimensional gapless systems: Does bosonization work? [|Emanuele Coira], [|Federico Becca] , [|Alberto Parola] <span style="background-color: #ffffff; display: block; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;">We present a comparison between the bosonization results for quantum quenches [M. A. Cazalilla, \prl {\bf 97}, 156403 (2006)] and exact diagonalizations in microscopic models of interacting spinless fermions in a one-dimensional lattice. We show that important features are missed by the bosonization technique, which predicts the persistence of long-wavelength critical properties in the long-time evolution. Instead, numerical analysis provides puzzling evidences: while the momentum distribution appears to be consistent with the presence of a singularity at $k_F$, density-density correlations at small momenta clearly display a thermal-like behavior, namely ${\bar{N}}_q \simeq {\rm const}$ (where the overbar indicates the long-time average). This feature at small momenta is preserved in presence of an interaction term that breaks integrability, together with a rounding of the singularities at finite $q$'s, showing that the bosonization approach is not able to represent the time evolution of generic one-dimensional models after a quantum quench.

<span style="background-color: #ffffff; display: block; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;"> 5. [|arXiv:1205.2859] (cross-list from nlin.PS) [ [|pdf], [|ps] , [|other] ] Matter-wave solitons with the minimum number of particles in two-dimensional quasiperiodic potentials [|Gennadiy Burlak], [|Boris A. Malomed] <span style="background-color: #ffffff; font-family: 'Lucida Grande',helvetica,arial,verdana,sans-serif; font-size: 14px;">We report results of systematic numerical studies of 2D matter-wave soliton families supported by an external potential, in a vicinity of the junction between stable and unstable branches of the families, where the norm of the solution attains a minimum, facilitating the creation of the soliton. The model is based on the Gross-Pitaevskii equation for the self-attractive condensate loaded into a quasiperiodic (QP) optical lattice (OL). The same model applies to spatial optical solitons in QP photonic crystals. Dynamical properties and stability of the solitons are analyzed with respect to variations of the depth and wavenumber of the OL. In particular, it is found that the single-peak solitons are stable or not in exact accordance with the Vakhitov-Kolokolov (VK) criterion, while double-peak solitons, which are found if the OL wavenumber is small enough, are always unstable against splitting.

= May 14 = 1. [|arXiv:1205.2683] [[|pdf], [|other]] The Avalanche Mechanism for Atom Loss near an Atom-Dimer Efimov Resonance [|Christian Langmack], [|D. Hudson Smith], [|Eric Braaten] An Efimov trimer near the atom-dimer threshold can increase the atom loss rate in ultracold trapped atoms through the {\it avalanche mechanism} proposed by Zaccanti et al. A 3-body recombination event creates an energetic atom and dimer, whose subsequent elastic collisions produce additional atoms with sufficient energy to escape from the trapping potential. We use Monte Carlo methods to calculate the average number of atoms lost and the average heat generated by recombination events in both a Bose-Einstein condensate and a thermal gas. We take into account the energy-dependence of the cross sections and the spatial structure of the atom cloud. We confirm that the number of atoms lost can be much larger than the naive value 3 if there is an Efimov trimer near the atom-dimer threshold. This does not produce a narrow loss feature, but it can significantly affect the determination of Efimov parameters.

2. [|arXiv:1205.2553] [[|pdf], [|ps], [|other]] Feshbach resonances in Cesium at Ultra-low Static Magnetic Fields [|D. J. Papoular], [|S. Bize], [|A. Clairon], [|H. Marion], [|S. J. Kokkelmans], [|G. V. Shlyapnikov] We have observed Feshbach resonances for 133Cs atoms in two different hyperfine states at ultra-low static magnetic fields by using an atomic fountain clock. The extreme sensitivity of our setup allows for high signal-to-noise-ratio observations at densities of only 2*10^7 cm^{-3}. We have reproduced these resonances using coupled-channels calculations which are in excellent agreement with our measurements. We justify that these are s-wave resonances involving weakly-bound states of the triplet molecular Hamiltonian, identify the resonant closed channels, and explain the observed multi-peak structure. We also describe a model which precisely accounts for the collisional processes in the fountain and which explains the asymmetric shape of the observed Feshbach resonances in the regime where the kinetic energy dominates over the coupling strength.