Controlling open quantum systems: Tools, achievements, limitations
Quantum control is an important prerequisite for quantum devices. A major obstacle is the fact that a quantum system can never completely be isolated from its environment. The interaction with the environment causes decoherence. Optimal control theory is a tool that can be used to identify control strategies in the presence of decoherence. I will show how to adapt optimal control theory to quantum information tasks for open quantum systems and present examples for cold atoms and superconducting qubits. The perspective on decoherence only as the adversary of quantum control is nevertheless too narrow. There exist a number of control tasks, such as cooling and measurement, that can only be achieved by an interplay of control and dissipation. I will show how to utilize optimal control theory to derive efficient cooling strategies for molecular vibrations where the timescales of coherent dynamics and dissipation are very different. Another opportunity for open system control, less obvious than cooling, arises from a coupling to the environment that results in non-Markovian dynamics. I will discuss how non-Markovianity of the open system time evolution can be exploited for control, using a superconducting phase circuit as example.

Dynamics of superfluid ⁶Li gases through a thin barrier
Quantum gases offer a unique toolbox for simulating complicated condensed matter problems. In particular, thanks to the fine control of the interaction strengths and of the trapping potentials, they provide unique opportunities to explore superfluidity phenomena. In our setup, we produce ⁶Li quantum gases across the BEC-BCS crossover. We superimpose on the fermionic superfluids a thin barrier, creating an analogue of a Josephson junction. We report our results on the study of the coherent dynamics in the different interactions regimes.

Noise in quantum simulators: from thermometry to entanglement
Noise and its correlations represent an essential probe of the nature of complex quantum systems. Fluctuations in quantum systems are both of thermal and quantum origin, and telling apart the thermal and quantum components of fluctuations is a formidable challenge. Nonetheless, accomplishing this task would give access to two fundamental aspects: the actual temperature of the quantum degrees of freedom, and their entanglement properties. Cold atoms trapped in light-induced potentials offer a unique opportunity to study noise in complex quantum systems, including the full noise statistics, either in momentum space (via time-of-flight images) or in real space (via in-situ images). In this talk I will first discuss how noise in momentum space can serve as an invaluable tool for thermometry for cold atoms via fluctuation-dissipation relations, generally valid for classical systems. The violation of such relations for quantum systems provides new insight into the structure of quantum fluctuations in momentum space. On the other hand, noise in real space -- in the form of local particle-number fluctuations -- is a direct manifestation of entanglement between a part of an extended quantum system and its complement. I shall discuss the analogies and discrepancies between the scaling laws of entanglement and fluctuations at zero temperature, and how fluctuations can serve as a fundamental entanglement witness at finite temperature.

Thermometry Precision in Strongly Correlated Ultracold Lattice Gases
The precise knowledge of the temperature of an ultracold lattice gas simulating a strongly correlated system is a question of both, fundamental and technological importance. Here, we address such question by combining tools from quantum metrology together with the study of the quantum correlations embedded in the system at finite temperatures. Within this frame we examine the spin-1/2 XY chain, first estimating, by means of the quantum Fisher information, the lowest attainable bound on the temperature precision. We then address the estimation of the temperature of the sample from the analysis of correlations using a quantum non demolishing Faraday spectroscopy method. Finally, we demonstrate that for sufficiently low temperatures the proposed measurements are optimal to estimate accurately the temperature of the sample.

Short-range quantum magnetism with ultracold fermions in optical lattices
In the last years ultracold Fermi gases in optical lattices have emerged as a new playground where traditional condensed matter phases, such as Mott insulators, quantum magnets or in the longer term high temperature superconductors could be explored with a high level of control. In my talk I will present experiments where a two-component repulsively interacting gas, which implements the Fermi-Hubbard model, is cooled to a regime where magnetic spin correlations emerge. In particular, we explore how certain crystal geometries favor short-range magnetic order, and directly probe the nearest-neighbor spin correlations of the gas. In a dimerized lattice, they manifest as an excess number of singlets as compared to triplets, whereas in an anisotropic simple cubic lattice we observe the appearance of antiferromagnetic correlations along one spatial axis. Our results are in good agreement with state-of-the-art numerical simulations and confirm that we achieve temperatures in the lattice below the exchange energy.

Interplay of micromotion and interactions in fractional Floquet Chern insulators
(Egidijus Anisimovas, Giedrius Zlabys, Brandon M. Anderson, Gediminas Juzeliunas, Andre Eckardt)
Floquet engineering is a particular form of quantum engineering based on the observation that the long-time dynamics of a periodically driven quantum system is described in terms of a time-independent effective Hamiltonian. On short time scales (within a driving period or so) one also observes the so-called micromotion which is associated to the periodic time-dependence of the Floquet modes and may be significant when the driving frequency is low. In this talk, I will: (i) present a systematic high-frequency expansion for the effective Hamiltonian and the micromotion operator of periodically driven quantum systems [1], and (ii) illustrate the method using the example of a driven hexagonal tight-binding lattice. In this system, qualitatively new physics (i.e. artificial fluxes and topological band structure) is induced by the second-order term in the high-frequency expansion of effective Hamiltonian. The possiblity to realize the fractional Floquet Chern insulating phases will be discussed paying particular attention to the interplay of micromotion and strong inter-particle interactions. [1] A. Eckardt and E. Anisimovas, arXiv:1502.06477v3 (2015).

Hydrodynamic modes of partially-condensed Bose mixtures
(J. Armaitis, H.T.C. Stoof, and R.A. Duine)
We generalize the Landau-Khalatnikov hydrodynamic theory for superfluid helium to two-component (binary) Bose mixtures at arbitrary temperatures. In particular, we include the spin-drag terms that correspond to viscous coupling between the clouds. Therefore, our theory not only describes the usual collective modes of the individual components, e.g., first and second sound, but also results in new collective modes, where both constituents participate. We study these modes in detail and present their dispersions using thermodynamic quantities obtained within the Popov approximation.

Quantifying tripartite entanglement dynamic of spin-1 bosons in optical superlattices
(Artur Barasiński, Wiesław Leoński)
We discuss a model with ultra-cold atoms confined in optical superlattices. In particular, entanglement dynamics of our system is analyzed. Applying the model involving three spin-1 bosons trapped in a triple-well potential, we have derived analytical formulas describing various types of entanglement between particles. Depending on the interactions strength between particles homogeneous and heterogeneous entanglement dynamics occur. We show that even for heterogeneous interactions case the homogeneous dynamic can be observed. Furthermore, we demonstrate and characterize the processes of the generation of genuine tripartite entangled states and W-like states from the initial product state. By tracing out one of discussed subsystems (bosons) maximally entangled bipartite states have been identified.

Out-of-equilibrium states and quasi-many-body localization in polar lattice gases
(L. Barbiero, C. Menotti, A. Recati, and L. Santos)
The absence of energy dissipation leads to an intriguing out-of-equilibrium dynamics for ultracold polar gases in optical lattices, characterized by the formation of dynamically-bound on-site and inter-site clusters of two or more particles, and by an effective blockade repulsion. These effects combined with the controlled preparation of initial states available in cold gases experiments can be employed to create interesting out-of-equilibrium states. These include quasi-equilibrated effectively repulsive 1D gases for attractive dipolar interactions and dynamically-bound crystals. Furthermore, non-equilibrium polar lattice gases can offer a promising scenario for the study of many-body localization in the absence of quenched disorder. This fascinating out-of-equilibrium dynamics for ultra-cold polar gases in optical lattices may be accessible in on-going experiments.

Scattering properties of strongly interacting Rydberg polaritons
(P.Bienias , S.Choi, O.Firstenberg, M.F.Maghrebi, M.Gullans, M.D.Lukin, A.V.Gorshkov, H. P. Buchler)
Recently, the combination of slow light polaritons with the strong interactions between Rydberg atoms has emerged as a promising system for inducing a strong interaction between photons. Potential applications range from the implementation of phase gates for photons, to single photon sources, as well as the generation of strongly correlated states of photons. In this talk, we present a theoretical framework describing slow-light polaritons interacting via atomic Rydberg states. The method allows us to analytically derive the scattering properties of two polaritons. We identify new parameter regimes where polariton-polariton interactions are repulsive. Furthermore, in the regime of attractive interactions, we identify multiple two-polariton bound states, calculate their dispersion, and study the resulting scattering resonances. Finally, we discuss the implications of our results to the ongoing experiments and to the effective many body theory for strongly interacting Rydberg polaritons.

Stability and spatial coherence of nonresonantly pumped exciton-polariton condensates
(Nataliya Bobrovska, Elena A. Ostrovskaya, and Michał Matuszewski)
We investigate the stability and coherence properties of one-dimensional exciton-polariton condensates under nonresonant pumping. We model the condensate dynamics using the open-dissipative Gross-Pitaevskii equation. In the case of spatially homogeneous pumping, we find that the instability of the steady state leads to significant reduction of the coherence length. We consider two effects that can lead to the stabilization of the steady state, i.e., the polariton energy relaxation and the influence of an inhomogeneous pumping profile. We find that, while the former has little effect on the stability, the latter is very effective in stabilizing the condensate, which results in a large coherence length.

Manipulation of cold atoms using Spatial Light Modulators
(Citlali Cabrera Gutierrez)
Spatial Light Modulators (SLM) have many applications in different domains of physics. I present here an application and a project for the near future to manipulate cold atoms with SLMs. First I present how, by using a SLM, we can create a blue-detuned Laguerre-Gaussian (LG) laser beam to highly collimate the cold atomic beam at the output of a 2D Magneto-Optical Trap. The cold atomic beam is collimated upto a diameter of about 1 mm. Therefore, the divergence is reduced from 40 down to 3 mrad and the atomic density is increased by a factor 200 [1]. The collimation effect has been optimized by adjusting the LG mode order (up to 10) and the laser detuning values (2-120 GHz). The collimated atomic beam could provide a new tool to load a 3D-MOT using lasers with millimeter range diameters and thus sparing the laser power. In a second part, I will present a proposal in which a SLM is used to shape the envelope of optical lattices, to perform novel quantum transport experiments with ultra-cold atoms. Indeed, an inhomogeneous envelope projects the gaps of optical lattices in space. Those spatial gaps have properties that are inaccessible by other means [2]. The SLM offers the possibility to control –almost at will - all the characteristics of those tunnel barriers. In particular they can be used to create atomic cavities, where effects such as the atom blockade could be observed [3]. [1] V. Carrat, C. Cabrera-Gutierrez, M. Jacquey, J. W. Tabosa, B. Viaris de Lesegno and L. Pruvost, Opt. Lett. 39 719-722 (2014). [2] P. Cheiney, F. Damon, G. Condon, B. Georgeot and D. Guery-Odelin, EPL 103, 50006(2013). [3] I. Carusotto, Phys. Rev. A 63, 023610 (2001).

'Light-cone' effect in short- and long-range interacting quantum systems
(G. Carleo, L. Cevolani, F. Becca, M. Fabrizio, S. Sorella, L. Sanchez-Palencia)
In this contribution I will present some recent results on the out-of-equilibrium dynamics of interacting quantum systems [1,2]. We study how (and how fast) correlations can spread in a quantum system abruptely driven out of equilibrium by a quantum quench. This protocol can be experimentally realized with ultra-cold atoms, which allow to address fundamental questions concerning the quasi locality principle in isolated quantum systems with both short- [3,4] and long-range interactions [5]. We focus on the spreading of correlations both in short-range [1] and long-range [2] Bose-Hubbard models, using time-dependent variational Monte Carlo simulations [6]. This method gives access to unprecedented long propagation times and to dimensions higher than one. In both one and two dimensions, we demonstrate the existence of a "light-cone", characterized by the ballistic spreading of correlations with a finite propagation time. In two dimensions the spreading presents interesting interference effects that I will discuss. The remarkable existence of a ballistic behavior even in the presence of extremely long-range interactions originates from a protection of the local modes that we have derived from a microscopic analysis. Further, I will discuss long-range interacting spin systems, where a breaking of locality is observed and fully characterized in terms of a quasi-particle microscopic analysis. [1] G. Carleo, F. Becca, L. Sanchez-Palencia, S. Sorella, and M. Fabrizio, Phys. Rev. A 89, 031602(R) (2014). [2] L. Cevolani, G. Carleo, and L. Sanchez-Palencia, arXiv:1503.01786 (2015). [3] M. Cheneau et al., Nature 481, 484 (2012). [4] T. Langen et al., Nat. Phys. 9, 640 (2013). [5] P. Richerme et al., Nature 511, 198 (2014). [6] G. Carleo, F. Becca, M. Schiro, and M. Fabrizio, (Nature) Sci. Rep. 2, 243 (2012).

Non-local order in a fermion system with correlated hopping.
(Ravindra Chhajlany, Przemyslaw Grzybowski, Julia Stasinska, Omjyoti Dutta, Maciej Lewenstein)
Strong correlated hopping inhibits certain hopping processes in a way akin to the effects of infinite on-site repulsion and leads to extreme correlation effects such as the appearance of projected particles and exotic phases. This makes systems with strong correlated hopping (SCH) an interesting playground for many-body theory. We introduce a one-dimensional fermionic model with non-standard correlated hopping, which in principle can be realized in experiments with ultra-cold gases on optical lattices. We present an exact solution of the model in the case of extreme correlations (X=t, X- correlated hopping, t-bare hopping) based on a so-called real-to-squeezed space mapping, which shows unambiguously that the system is characterized by a non-local order parameter. Away from extreme correlations (X=t) case we present numerical results arguing for the existence of non-local order up to the X=0 limit. Finally we discuss the possibility of interpreting the non-locally ordered state as a critical exotic hole superconductor.

Fast production of metastable Helium Bose-Einstein condensates
(Q. Bouton, R. Chang, L. Hoendervanger, F. Nogrette, A. Aspect, C. Westbrook and D. Clément)
I will report on the construction of a novel experimental apparatus dedicated to the study of momentum-space correlations in ultra cold gases of metastable Helium atoms. The new machine produces large Bose-Einstein condensates (BECs) in a crossed optical dipole trap with an experimental cycle of 8 seconds, much shorter than previously reported with Helium species. This is possible thanks to the implementation of recent techniques developed for other atomic species, in particular the use of gray molasses and that of an hybrid trap (magnetic quadrupole and optical dipole trap) to efficiently load the crossed dipole trap. In the near future, the Helium BECs will be loaded into three-dimensional optical lattices to investigate momentum correlations of lattice bosons. The special properties of metastable Helium (large internal energy and light mass) will allow us to reconstruct the position and correlation between individual atoms after a long time-of-flight, yielding novel information on the quantum depletion phenomenon and the critical region of the Superfluid-to-Mott transition.

Quantum insulation in nanoscale heat devices
(Luis A. Correa)
The direction of the steady-state heat currents across a generic quantum system connected to multiple baths may be engineered so as to realize virtually any thermodynamic cycle (e.g. an absorption chiller, a heat transformer or even a heat engine). In spite of their versatility, such devices are generally unable to operate at large efficiencies due to undesired sources of irreversibility. In particular, we study a minimal model of absorption chiller allowing for heat leaks. These are shown to have a seizable negative impact on both performance and cooling load. However, once the underlying mechanism responsible for the losses is identified, these may be fully suppressed by decoupling the system from the large frequency components of the heat baths. This suggest that the use of reservoir engineering techniques can significantly improve the performance of realistic nanoscale heat devices for potential applications to quantum technologies.

Using driven cold atoms as quantum simulators
(C.E. Creffield, G. Sierra, and F. Sols)
Ultracold atoms held in optical lattice potentials provide a powerful and flexible way to study coherent quantum phenomena. Periodically driving, or "shaking", the lattice can produce an effect termed coherent destruction of tunneling, in which the driving can be used to control the intersite tunneling via quantum interference effects. I will first show how to regulate the amplitude of the tunneling so that it mimics the Riemann zeta function [1], allowing the Riemann zeros to be directly observed in currently accessible cold atom experiments. I will then show how the phase of the tunneling can also be controlled, permitting the simulation of synthetic magnetic fields [2] over the complete range of field strengths, reproducing the "Hofstadter butterfly" band structure. [1] C.E. Creffield and G. Sierra, http://arxiv.org/abs/1411.0459. [2] C.E. Creffield and F. Sols, Phys. Rev. A 90, 023636 (2014).

Variational Approach to Projected Entangled Pair States at Finite Temperature
(Piotr Czarnik and Jacek Dziarmaga)
The projected entangled pair state (PEPS) ansatz can represent a thermal state in a strongly correlated system. We introduce a novel variational algorithm to optimize this tensor network. Since full tensor environment is taken into account, then with increasing bond dimension the optimized PEPS becomes the exact Gibbs state. Our presentation opens with a 1D version for a matrix product state (MPS) and then generalizes to PEPS in 2D. Benchmark results in the quantum Ising model are presented.

Hamiltonian design in atom-light interactions with rubidium ensembles
(M. Dąbrowski, R. Chrapkiewicz and W. Wasilewski)
We present an experimental demonstration of the Hamiltonian manipulation in light-atom interface in Raman-type warm Rb-87 vapor atomic memory. By adjusting the detuning of the driving beam we varied the relative contributions of the Stokes and anti-Stokes scattering to the process of four-wave mixing at the readout stage. Our experimental results agree quantitatively with a simple, plane-wave theoretical model we provide (Opt. Express 22 (21), 26076-26090 (2014)). Measured correlation maps enabled us to resolve between the anti-Stokes and the Stokes scattering and to quantify their contributions. The Stokes contribution yields additional, adjustable gain at the readout stage, albeit with inevitable extra noise. We provide useful framework to trace it and the results can be utilized in the existing atomic memories setups. Furthermore, the shown Hamiltonian manipulation offers a broad range of atom-light interfaces readily applicable in current and future quantum protocols with atomic ensembles.

Strongly Interacting One-Dimensional Bose Systems and Bose Polarons
(A. S. Dehkharghani , A. G. Volosniev, E. J. Lindgren, J. Rotureau, C. Forssen, D. V. Fedorov, A. S. Jensen and N. T. Zinner)
Strongly interacting one-dimensional quantum systems often behave in a manner that is distinctly different from their higher-dimensional counterparts. When a particle attempts to move in a one-dimensional environment it will unavoidably have to interact and 'push' other particles in order to execute a pattern of motion, irrespective of whether the particles are fermions or bosons. A present frontier in both theory and experiment are mixed systems of different species and/or particles with multiple internal degrees of freedom. Here we consider trapped two-component bosons with short-range inter-species interactions much larger than their intra-species interactions and show that they have novel energetic and magnetic properties. In the strongly interacting regime, these systems have energies that are fractions of the basic harmonic oscillator trap quantum and have spatially separated ground states with manifestly ferromagnetic wave functions. Furthermore, we predict excited states that have perfect antiferromagnetic ordering. This holds for both balanced and imbalanced systems, and we show that it is a generic feature as one crosses from few- to many-body systems. In addition we setup a new theoretical framework in one-dimension for describing and calculating the ground state energy for an impurity in a N-boson system. Our theory works for any number of N bosons as majority particles and also adaptive to any external confinement, arbitrary mass ratios and even small but non-zero intra-species interaction strength. The results for 1+8 polaron system show very well agreement with the numerically exact results and thus our theory can provide definite predictions for the experiments in cold atomic gases at zero temperatures.

The applicability of complex field descriptions of ultracold Bose gases
(Piotr Deuar, Joanna Pietraszewicz, Tomasz Świsłocki)
A ``classical fields' description is commonly used to describe quantum Bose gases in conditions when the condensate fraction is far below one, yet the majority of states are still highly occupied. It is unique in being able to describe nonlinear effects and defects in single-realizations of a quantum gas with macroscopic numbers of particles. The approach takes several guises, be it direct replacement of field operators with complex fields, stochastic Gross-Pitaevskii equations (SGPEs), or a truncated Wigner approach that includes initial state vacuum fluctuations. The accuracy of such descriptions, has, however been only vaguely constrained, and it is a matter of debate whether results can only be interpreted as broadly qualitative in nature, or whether quantitative comparison to experiments can be meaningfully made. We report on detailed studies of the region of applicability of c-field descriptions. We find that their breakdown manifests itself most strikingly as the inability to simultaneously properly describe density fluctuations and kinetic energy. We pinpoint the regimes for which less than 10% error in common observables can be counted on. Importantly, a 2D gas never reaches this regime, and is poorly described even as temperature falls to zero. Time permitting, I will also discuss an extended form of the SGPE that allows one to include the effect of quantum fluctuations in a c-field equilibrium ensemble.

Quantum Kibble-Zurek mechanism
(Bartek Gardas, Jacek Dziarmaga, Wojciech H. Zurek)
I will present our brute force DMRG simulations of the dynamical Mott-to-superfluid quantum phase transition in a 1D optical lattice.

Towards sub-micron trapping of cold atoms for magnetic microscopy
(A. Gadge, T. James, J. Ferreras, J. Maclean, Ch. Mellor, M. Fromhold, F. Intravaia, Ch. Koller, F. Orucevic, and P. Kruger)
Cold atoms are extremely sensitive to the potential in which they are trapped. This makes them ideal as magnetic and electric field sensors.To achieve higher resolution, the separation of trapped atoms from the surface needs to be reduced. Minimum trapping distances possible with current magnetic microtraps are limited by various surface effects. In the sub-micron regime most dominant effects leading to loss of trapped atoms are Casimir force and Johnson noise. To enable ultraclose trapping of atoms, we will show possibilities of using different surfaces such as silicon nitride membranes and graphene which have reduced surface effects. In order to achieve higher atom number in the initial trapping stages, we use a novel technique of dual color MOT of Rb87 atoms. We have designed a printed circuit board to transport and precisely position the cloud at any desired position above the sample. We will show theoretical calculations and current experimental progress.

Hybridization of Rydberg electron orbitals by molecule formation
(A. Gaj, A. T. Krupp, P. Ilzhöfer, R. Löw, S. Hofferberth, T. Pfau)
The formation of ultralong-range Rydberg molecules is a result of the attractive interaction between Rydberg electron and polarizable ground state atom in an ultracold gas. In the nondegenerate case the backaction of the polarizable atom on the electronic orbital is minimal. We demonstrate, how controlled degeneracy of the respective electronic orbitals maximizes this backaction and leads to stronger binding energies and lower symmetry of the bound dimers. Consequently, the Rydberg orbitals hybridize due to the molecular bond.

Dressing up for quantum technology
(Barry Garraway and German Sinuco)
We will review the development of atomic dressing for the control of cold atoms. Dressing with radio-frequency and microwave radiation opens new atom trap designs because of the flexibility inherent in the vector coupling of a magnetic dipole moment to EM fields which can be varied in time, frequency, orientation and space. This may in turn result in quantum technology applications to sensing, metrology and interferometry. This talk will introduce the concept of the dressed atom, and present both old and new designs of ring traps [1,2] and race tracks [3] with potential to make new atomic gyroscopes. [1] O.Morizot, Y.Colombe, V.Lorent, H.Perrin, and B.M.Garraway, Phys. Rev. A 74, 023617 (2006). [2] M.Vangeleyn, B.M.Garraway, H.Perrin, A.S.Arnold, J. Phys. B 47, 071001 (2014) . [3] G.Sinuco-Leon, K.Burrows, A.S.Arnold, and B.M.Garraway, Nat. Commun. 5, 5289 (2014).

Static structure factor for an elongated Bose-Einstein condensate
(M. Brewczyk K. Rzazewski)
We investigate phonon population in an elongated Bose-Einstein condensate. It was shown in a recent experiment [1] that in fully 3D condensate the thermal phonons distribution obeys expected Planck law. This is not true in a quasi-1D condensate, because of deep dark solitons which are present in the system. Thermal solitons do occur spontaneously in the 1D-system and affect the density fluctuation, thus changing the phonon distribution. We proof that by calculating the static structure factor in a way suggested in Ref. [1]. [1] R. Schley, A. Berkovitz, S. Rinott, I. Shammass, A. Blumkin, and J. Steinhauer Phys. Rev. Lett. 111, 055301 (2013).

Artificial magnetic fluxes and topological phenomena in spin chains with long-range interactions
(Tobias Grass (ICFO), Christine Muschik (IQOQI), Ravindra Chhajlany (ICFO), Alessio Celi (ICFO), Maciej Lewenstein (ICFO))
In the presence of long-range interactions loops with non-zero magnetic flux can appear even in one-dimensional systems. We propose the realization of such scenario in spin chains of atoms coupled to photonic waveguides, or trapped ions. Magnetic fluxes can be induced via periodic driving. For such system, we calculate Chern numbers and edge spectra, demonstrating the occurrence of topological phases. Varying the magnetic flux, the system exhibits a fractal energy spectrum similar to the Hofstadter butterfly.

Many interacting fermions in a 1D harmonic trap: a quantum chemist's perspective
(Tomasz Grining, Michal Tomza, Michal Lesiuk, Michal Przybytek, Monika Musial, Pietro Massignan, Robert Moszynski, Maciej Lewenstein)
State-of-the-art quantum many-body methods of quantum chemistry have been employed to investigate spin-1/2 fermions, interacting via a two-body contact potential, in a one-dimensional harmonic trap. Benchmark calculations for two to six fermions with the full configuration interaction method (FCI), equivalent to the exact diagonalization approach, and the coupled cluster method (CC) including single, double, triple, and quadruple excitations are presented. The convergence of the total and correlation energies with the size of the single-particle basis set and the level of excitations included in the coupled cluster model is analyzed. Next, the coupled cluster method restricted to single, double, and noniterative triple excitations, CCSD(T), is employed to describe the two-component Fermi gas of ten to sixty atoms in a one-dimensional harmonic trap. The importance of the post-CCSD(T) contributions is analyzed. The method is applied to explain recent experimental results for a few atoms in a trap, such as the separation energy related to the BCS pairing of the electrons and to describe the transition from a few-body to many-body regime, and even to the thermodynamical limit.

Level correlations and chaos in the presence of overlapping Feshbach resonances
(Krzysztof Jachymski, Paul S. Julienne)
Short-range anisotropies in the interaction potentials of lanthanide atoms result in extremely dense sets of Feshbach resonances. The statistics of the resonance spacings in erbium has recently been studied experimentally [1] and showed features characteristic for chaotic systems described by Random Matrix Theory (RMT). Here we study theoretically how the mutual interaction of overlapping resonances influences the resonance spacings. In our analysis we make use of a simple quantum-defect model, which provides analytical formula for the scattering length [2]. We find out that the statistical properties of resonance spacings may resemble chaotic behavior even if the assumptions of RMT are not fulfilled. Our results are in good agreement with experiment. [1] Frish et al., Nature 507, 475-479 (2014) [2] Jachymski and Julienne, Phys. Rev. A 88, 052701 (2013)

Dynamical generation of quantum states for high-precision measurements by two-axis counter-twisting hamiltonian.
(Darek Kajtoch, Emilia Witkowska)
We will review properties of two-axis counter-twisting (TACT) hamiltonian proposed by Kitagawa & Ueda for dynamical generation of spin squeezed states. TACT hamiltonian gives better spin squeezing than widely studied one-axis twisting hamiltonian. Moreover, Heisenberg like scaling with the system size of the quantum Fisher information can be achieved during time evolution. We identify various quantum states and show both Husimi and Wigner function maps at different moments of time. Phase space quantum dynamics localizes near mean-field trajectories. Presence of classical saddle fixed point is responsible for both high squeezing level and complicated dynamics in further moments of time. Additionally, effect of phase noise on the quantum Fisher information and spin squeezing will be discussed.

Losses and oscillations of the Bose-Einstein condensate induced by Rydberg atoms
(Tomasz Karpiuk, Miroslaw Brewczyk, Kazimierz Rzazewski, Anita Gaj, Jonathan B. Balewski, Alexander T. Krupp, Michael Schlagmuller, Robert Low, Sebastian Hofferberth, Tilman Pfau)
In the recent experiment [1] a series of Rydberg atoms in s-state was excited in the Bose-Einstein condensate. Interaction between Rydberg atoms and ground level atoms caused that some amount of ground level atoms was promoted to the thermal cloud. Secondly also a mechanical effect was present showing itself in the form of shape oscillations of the condensate. In the present work we compare experimental results not only for s-states but also for d-states with the theoretical approach introduced in [2]. This approach was based on the assumption that condensate atoms, while interacting with the laser light, perform Rabi oscillations independently. Here we modify this assumption by introducing the mechanism of collective Rabi oscillations and try to answer the question which approach better describes a system of a single Rydberg atom embedded in the Bose-Einstein condensate. [1] J. B. Balewski, A. T. Krupp, A. Gaj, D. Peter, H. P. Buchler, R. Low, S. Hofferberth, and T. Pfau, Nature 502, 664 (2013). [2] T. Karpiuk, M. Brewczyk, K. Rzazewski, A. Gaj, J. B. Balewski, A. T. Krupp, M. Schlagmuller, R. Low, S. Hofferberth, T. Pfau, arXiv:1402.6875

Feshbach resonances without a bound state in a closed channel
(M. M. Krych, T. Wasak, Z. Idziaszek, M. Trippenbach, Y. Avishai, and Y. B. Band)
We use the Numerov's method and the dressed potentials obtained in the adiabatic representation of coupled channels to calculate s-wave Feshbach resonances in a three-dimensional spherically symmetric potential. Analytic expressions for the s-wave scattering length and number of resonances are obtained for a piecewise constant model with a piecewise constant interaction of the open and closed channels near the origin. We show analytically and numerically that, for strong enough coupling strength, Feshbach resonances can exist even when the closed channel does not have a bound state.

Thermal blurring of a coherent Fermi gas
(Hadrien Kurkjian, Yvan Castin and Alice Sinatra)
Coherent gases of ultracold atoms confined in immaterial non-dissipative traps are unique examples of isolated macroscopic quantum systems. The value of their intrinsic coherence time is then a fundamental question. But it is also a practical issue for all the applications which exploit macroscopic coherence, such as interferometry, or quantum engineering where one generates non-trivial entangled states by coherent evolution. Coherence time measurements are presently being performed in cold Bose gases. Experiments on Fermi gases, that up to now focussed on traditional aspects of the $N$-body problem, such as thermodynamic properties, are moving towards correlation and coherence measurements. This turn will open a new research field, including the strong coupling regime : that of fermionic quantum optics. However, a theory predicting the coherence time of a pair-condensed Fermi gas was missing, except in the limiting case of zero temperature. In this paper we present the first microscopic theory bridging this theoretical gap in a general way. Our results hold for other physical systems, such as mesoscopic Josephson Junctions, provided that the environment-induced decoherence is sufficiently reduced.

Theory of dynamic structure factor and drag force in a one-dimensional strongly-interacting Bose gas at finite temperature
(Guillaume Lang, Frank Hekking, Anna Minguzzi)
Generalizing Landau's criterion for superfluidity, Astrakharchik and Pitaevskii (Phys. Rev. A 70, 013608, 2004) proposed to probe this property in degenerate gases by studying the dynamic structure factor. In the framework of linear response theory, given a potential barrier stirred in the fluid at a velocity v, they showed that one can compute the drag force F acting on the barrier from the dynamic structure factor. A signature of superfluidity is that F(v)=0 in a certain range of velocities. Generalizing their work, I study the effect of both thermal and quantum fluctuations on the dynamical response of a one-dimensional strongly-interacting Bose gas in a tight atomic waveguide. Combining the Luttinger liquid theory at arbitrary interactions and the exact Bose-Fermi mapping in the Tonks-Girardeau impenetrable boson limit, I obtain the dynamic structure factor of the strongly-interacting fluid at finite temperature. Then, I determine the drag force felt by a potential barrier moving across the fluid in the experimentally realistic situation of finite barrier width and temperature.

Numerical Simulations with Finite PEPS
(Michael Lubasch, Juan Ignacio Cirac, Mari-Carmen Ba~{n}uls)
Projected Entangled Pair States (PEPS) are a promising ansatz for the study of strongly correlated quantum many-body systems in two dimensions. They are the natural generalization of the very successful Matrix Product States (MPS) in higher dimensions. But while MPS are well established and widely used for the simulation of one-dimensional quantum many-body systems, PEPS algorithms are more complicated and currently considered only by a much smaller community. We will discuss the key algorithmic aspects of finite PEPS and present state-of-the-art simulation results [1, 2]. [1] M. Lubasch, J. I. Cirac, M.-C. Ba~{n}uls, New J. Phys. 16, 033014 (2014). [2] M. Lubasch, J. I. Cirac, M.-C. Ba~{n}uls, Phys. Rev. B 90, 064425 (2014).

Controlling disorder with periodically modulated interactions
(Arkadiusz Kosior, Jan Major, Marcin Płodzień, Jakub Zakrzewski)
We investigate a celebrated problem of one dimensional tight binding model in the presence of disorder leading to Anderson localization from a novel perspective. A binary disorder is assumed to be created by immobile heavy particles for the motion of the lighter, mobile species in the limit of no interaction between mobile particles. Fast periodic modulations of interspecies interactions allow us to produce an effective model with small diagonal and large off-diagonal disorder unexplored in cold atoms experiments. We present an expression for an approximate Anderson localization length and verify the existence of the well known extended resonant mode and analyze the influence of nonzero next-nearest neighbor hopping terms. We point out that periodic modulation of interaction allow disorder to work as a tunable band-pass filter for momenta.

Unusual robust phase coherence in a coupled boson-fermion system
(Maciej Maska)
We consider a coupled boson-fermion model in two dimensions, that describes itinerant fermions hybridizing with localized bosons composed of pairs of tightly bound opposite–spin fermions. We trace out the fermionic degrees of freedom and perform a Monte Carlo simulation for the effective classical Hamiltonian of boson phases. We find that the fermions not only generate an effective long-range temperature-dependent boson-boson coupling that generates a finite phase stiffness, but remarkably the phase stiffness is considerably more robust than that described by the XY model. Our analysis further shows that the fermion-boson hybridization leads to an effective long-range temperature-dependent interaction between the boson phases, with inter-vortex interaction in the effective model that is a power law rather than logarithmic as in the XY model.

Localized states in one-dimensional exciton-polariton condensates
(M. Matuszewski, Y. Xue, M. Kulczykowski, N. Bobrovska)
We investigate the properties of exciton-polariton condensates in a one-dimensional structure, such as a narrow microwire. The dissipative nature of the condensate gives rise to a variety of localized solutions [1]. We predict the existence of analogues of Bekki-Nozaki holes of the complex Ginzburg-Landau equation [2], which are continuations of conservative dark solitons, and bright sinks [3], which have no analogue in the conservative Gross-Pitaevskii model. [1] W. van Saarloos, P.C. Hohenberg, Physica D 56, 303 (1992). [2] Y. Xue and M. Matuszewski, Phys. Rev. Lett. 112, 216401 (2014). [3] M. Kulczykowski, N. Bobrovska and M. Matuszewski,. arXiv:1501.07791.

Measuring Full Correlation Probability Distributions in Ultracold Lattice Gases using a Faraday Interface
(M. Moreno-Cardoner, G. De Chiara)
Light-matter interfaces provide a powerful tool for the detection, control and manipulation at the quantum level. In particular, the Faraday spectroscopy used in cold atomic ensembles provides a non-demolition measurement for atomic correlations. Here, one can experimentally measure the rotation of the light polarization of a laser beam, induced by the strong coupling with the collective magnetic moment of the atoms, and in this way, indirectly measure the atomic correlations that are faithfully imprinted on the light polarization. Moreover, this scheme allows to access any order of the statitstical moments of the total magnetization of the atomic sample, or equivalently, the full probability distribution corresponding to this observable. Here, we analyze for different spin models how this distribution changes accross different types of phase transitions (continuous and discontinuous) and characterize them using critical exponents in the thermodynamic limit. Moreover, we study the non-classical properties of the emerging light after the measurement takes place.

Comparison of two strontium optical lattice clocks
(P. Morzynski, M. Bober, A. Cygan, D. Lisak, P. Maslowski, R. Ciurylo, J. Zachorowski, W. Gawlik, C. Radzewicz, M. Zawada)
We present a system of two independent strontium optical lattice standards probed with a single shared ultra-narrow laser. We report hertz-level spectroscopy of the clock line of strontium atoms confined in 1D lattice and relative stability of 2*10^(-15). The absolute frequency of the clock line is calibrated to the hydrogen maser via the OPTIME fiber network by the use of the Er:fiber optical frequency comb.

Topological Bound States generated by Cold Atoms performing a Quantum Walk
(S. Mugel, A. Celi, P. Massignan, M. Lewenstein and C. Lobo)
We suggest protocols for building a discrete-time quantum walk with ultracold atoms in a one dimensional lattice. The particle’s intrinsic spin is represented by the atom’s Zeeman levels. The spin dependent shift operation is implemented by time evolving the system for a fixed amount of time. Short pulse Raman transitions are used to induce instantaneous spin mixing operations. By changing the system's parameters, we are able to generate well localized zero energy states, which are symmetry protected.

Dynamics and Thermalization of a Fermion Embedded in Two Fermionic Baths
(Michael Mwalaba, Ilya Sinayskiy, Francesco Petruccione)
We consider a system consisting of a spinless electron which is strongly interacting with a finite bath of spinless electrons. This system is weakly interacting with a Markovian bath consisting of an infinite number of spinless electrons. We derive the master equation describing the dissipative dynamics of the system and based on this master equation, the reduced dynamics and thermalization of the electron of interest is studied.

Purification of a BEC through filtering excited Spin states
(B. Naylor, J. Huckans, E. Maréchal, L. Vernac, O. Gorceix and B. Laburthe-Tolra)
We studied the thermodynamic properties of chromium atoms at low magnetic field. Due to the anisotropy of dipolar interactions, magnetization is free and adapts to temperature. We observe that the BEC always forms in the lowest energy Zeeman state [1]. By applying a magnetic field gradient, we introduce a selective loss of atoms in spin-excited states, which provides a specific loss channel for thermal atoms. This new cooling mechanism based on spin filtering results in a purification of the BEC and an increased phase-space density. Contrarily to evaporative cooling where efficiency drops when T<gn, this new cooling mechanism is expected to be efficient even when T<<gn. This cooling mechanism can be generalized to atoms with negligible dipolar interactions such as alkali atoms. In this case, we suggest to use a positive quadratic field to favor BEC in mS=0. Then excited spin states are populated by thermal atoms through contact spin changing collisions and we estimate that in presence of a quadratic field sub-nK temperatures may be obtained. [1] B. Pasquiou, E. Maréchal, L. Vernac, O. Gorceix and B. Laburthe-Tolra, Phys. Rev. Lett. 108 , 045307 (2012).

Quantum simulation with cold atoms and ions.
(Antonio Negretti, Rene Gerritsma, Ulf Bissbort, Daniel Cocks, Zbigniew Idziaszek, Tommaso Calarco, Walter Hoffstetter, and Ferdinand Schmidt-Kaler)
Trapped ultracold atoms and ions in electromagnetic traps have been proven to be among the most successful systems in order to study quantum many-body systems through quantum simulators due to their high degree of control. Up to now, these systems have been studied separately, but in the last few years the technological progress in trapping and cooling has enabled experimental physicists to combine these systems in order to investigate new physics. These experimental achievements open very new research perspectives and challenges both at the experimental and theoretical level. In particular, such hybrid atomic systems allow investigating condensed-matter systems more closely: for instance, an important component of a solid-state system is the charge-phonon coupling, which is mimicked naturally in an atom-ion system. This feature is absent in ultracold atoms trapped in an optical lattice, where there is no back-action of the atoms on the lattice. Here I shall report on recent theoretical investigations concerning the hybrid atom-ion system. In particular, I shall present how such a system can be used in order to simulate solid-state physics and how atom-ion entanglement can be generated. Besides, the effects of experimental issues such as imperfect ground state cooling of the ion and the impact of micromotion are analyzed.

Bell-Paired States Inducing Volume Law for Entanglement Entropy in Fermionic Lattices
(G. Gori, S. Paganelli, A. Sharma, A, Trombettoni, P. Sodano)
We show that a violation of the area law for the EE may emerge in fermionic lattices, for long-range hoppings together with a suitable choice of the topology of the Fermi surface. The EE can be maximized by a ground state composed by Bell-paired states generated with two states belonging respectively only to the subsystem for which we wish to determine the EE and its complement. For translational invariant one-dimensional systems these states are obtained at half-filling occupying, according to the Fermi statistics, all even (or odd) wavevectors, corresponding to a “zigzag” alternate Fermi surface in momentum. We relate this dense occupation in momentum space with its (bounding box) fractal dimension. We give some examples of Hamiltonians designed to create entanglement among different parts of the system for which deviations from the area law may emerge. Finally, we present first numerical results for a tight-binding Hamiltonian with random long-range hoppings.

Dipolar dark solitons
(Krzysztof Pawlowski, Kazimierz Rzazewski)
I will discuss properties of dark solitons in a dipolar gas confined in a quasi one dimensional trap. As one may expect, the dark solitons in dipolar gas interact with themselves. To a good approximation, the movement of a pair of solitons can be thought as movement of two fictitious particles within an effective potential. The first peculiarity of this system is, that this effective potential has a local extrema, thus it supports bound states of solitons. On the other hand collisions between solitons are not elastic. Here colliding solitons can emit phonons, hence they can loose an energy, but at the same time they accelerate. The resulting gray solitons are sufficiently energetic to pass through the shallow inter-solitonic potential practically unperturbed. In the second part of the talk I will discuss spontaneous emergence of the solitons in thermal samples of a dipolar gas.

Two-flavor mixture of a few fermions of different mass in a one-dimensional harmonic trap
(Daniel Pecak, Mariusz Gajda, Tomasz Sowinski)
A system of two species of fermions of different mass confined in a one- dimensional harmonic trap is studied with an exact diagonalization approach. It is shown independently on the number of particles that a mass difference between fermionic species induces a separation in the lighter flavor system. The mechanism of emerging of separated phases is explained phenomenologically and confirmed with the help of a direct inspection of the ground-state of the system. Finally, it is shown that the separation driven by a mass difference, in contrast to the separation induced by a difference of populations, is robust to the interactions with thermal environment. [1] D. Pęcak, M. Gajda, T. Sowiński, ArXiv:1506.03592 (2015).

Laguerre-Gaussian laser modes for atomic physics experiments : atom channeling and information storage
(Laurence Pruvost)
Laguerre-Gaussian laser modes are ring of light having a helical phase. Their phase structure is known to be responsible of an orbital angular momentum (OAM) of light. This quantity is quantified by an integer ℓ and the Laguerre-Gaussian mode basis constitutes a way to encode the information. The two properties - annular intensity and helical phase - are used in the context of atomic physics either to manipulate the atoms or to store quantum information in an atomic ensemble. This talk will present the Laguerre-Gaussian laser modes, their properties and the methods to generate them. Then two examples will be given in atomic physics: (1) Long-distance channeling of cold atoms exiting a 2D magneto-optical trap by a Laguerre-Gaussian laser beam [1]. In this experiment done in Orsay, by using a blue-detuned laser shaped into a Laguerre-Gaussian (LG) mode, we channel atoms exiting a 2–dimensional magneto-optical trap (2D-MOT) over a 30 cm distance. Compared to a freely propagating beam, the atomic flux (about 1010at/s) is conserved whereas the divergence is reduced from 40 to 3 mrad. So, 30 cm far from the 2D-MOT exit, the atomic beam has 1 mm diameter and the atomic density is increased by a factor of 200. Such a LG-channeled-2D-MOT with a high density flux is a promising device for many applications as, for example, loading a 3D-MOT. The device has been studied versus the order of the LG mode (from 2 to 10) and versus the laser-atom frequency detuning (from 2 to 120 GHz). A clever version in which the LG mode frequency is locked to the repumping transition allows us to run the setup with two lasers instead of three. (2) Storage and Non-Collinear Retrieval of Orbital Angular Momentum of Light in Cold Atoms [2]. Using a nonlinear interaction of OAM beams with a cold atomic ensemble via four-wave mixing (FWM) processes it has been demonstrated that OAM can be stored and retrieved, via EIT process, allowing atomic memories. Differently from the previous observations, we demonstrated that the stored OAM beam is retrieved along a non-collinear direction. The experiment in collaboration with Tabosa’s group (Recife) is performed in cold Cs atoms obtained from a MOT, using a delayed FWM configuration with a writing beam W with topological charges ℓ=0,1,2,3. The phase structure is stored into the Zeeman coherence grating induced by the incident writing beams and is restored when a reading beam is switched on. The retrieved beam, monitored by a CCD camera, shows the transfer and conservation of OAM. Recently we have realized OAM storage and addition using CPO (coherent population oscillations). [1] V. Carrat, C. Cabrera-Gutiérrez, M. Jacquey, J. W. Tabosa, B. Viaris de Lesegno, and L. Pruvost, “Long-distance channeling of cold atoms exiting a 2D magneto-optical trap by a Laguerre–Gaussian laser beam”, Opt. Lett. 39, 719-722, 2014. [2] R. A. de Oliveira,L. Pruvost, P. S. Barbosa,W. S. Martins,S. Barreiro, D. Felinto,D. Bloch,J. W. R. Tabosa Off-axis retrieval of orbital angular momentum of light stored in cold atoms, Appl. Phys. B, 117, 1123, 2014

Towards AC-induced optimum control of dynamical localization
(F. Revuelta, R. Chacon, and F. Borondo)
In this work, we show [1] that optimum control of dynamical localization (quantum suppression of classical diusion) in the context of ultracold atoms in periodically shaken optical lattices depends on the impulse transmitted by the external modulation over half-period rather than on the modulation amplitude. This result provides a useful principle for optimally controlling dynamical localization in general periodic systems, which is capable of experimental realization. [1] F. Revuelta, R. Chacon, and F. Borondo, arXiv:1409.4454 [quant-ph].

Tunneling spectroscopy of few interacting Fermi atoms
(M. Rontani and P. D'Amico)
We develop a theory for the tunneling of a single atom or a correlated pair out of a trap containing few interacting cold atoms. In the repulsive regime the quasiparticle wave function, dressed by the interaction with the companion atoms in the trap, replaces the non-interacting orbital at resonance in the tunneling matrix element [1]. The computed tunneling time for two 6Li atoms agree with recent experimental results [2], unveiling the `fermionization' of the wave function and a novel two-body effect [1]. For attractive interactions we add the possibility that two atoms tunnel as a bound pair [3], leading to qualitative agreement with the measured two-atom decay time [4]. Using exact diagonalization [5] to treat up to six fermions with balanced spin population, we find evidence of BCS-like pairing [6]. For moderate interaction strength, we reproduce the even-odd oscillation of the separation energy observed in [4]. For strong interatomic attraction the arrangement of dimers in the trap differs from the homogeneous case as a consequence of Pauli blockade in real space. This work is supported by Marie Curie ITN INDEX and MIUR-PRIN MEMO. [1] M. Rontani, Phys. Rev. Lett. 108, 115302 (2012). [2] G. Zuern et al., Phys. Rev. Lett. 108, 075303 (2012). [3] M. Rontani, Phys. Rev. A 88, 043633 (2013). [4] G. Zuern et al., Phys. Rev. Lett. 111, 175302 (2013). [5] P. D'Amico and M. Rontani, J. Phys. B 47, 065303 (2014). [6] P. D'Amico and M. Rontani, Phys. Rev. A (2015), in press.

Anderson localization and Mott insulator phase in the time domain
(Krzysztof Sacha)
Particles in space periodic potentials constitute standard models for investigation of crystalline phenomena in solid state physics. Time periodicity of periodically driven systems is a close analogue of space periodicity of solid state crystals. Here we show that periodically driven systems are able to reveal non-trivial crystal-like phenomena in the time domain. If a periodically driven single-particle system is subjected to an additional perturbation that fluctuates in time, Anderson localization effects can be observed in the time domain. Switching to many-particle systems we show that depending on how strong particle interactions are, stationary states reveal long-time phase coherence or such a coherence is lost because stationary states are single Fock states where definite numbers of particles occupy periodically evolving localized wave-packets.

Triangular and Honeycomb Lattices of Cold Atoms in Optical Cavities
(Shabnam Safaei, Christian Miniatura and Benoit Gremaud)
In a system consisting of two optical cavities and a cloud of non-interacting cold Bosons, pumped by a laser field in dispersive regime, we examine the possibility of formation of triangular and honeycomb lattices of cold atoms as a result of superradiance and self-organization. We consider a two-dimensional homogenous ensemble of cold atoms inside two optical cavities pumped by a laser field, which is far-detuned from the atomic transition and slightly-detuned from the cavity modes. For laser strengths larger than a critical value, we show that while the atoms scatter the laser field into the cavity modes collectively, superposition of the standing waves of the laser and the cavity fields creates an effective potential for the atoms to self-organize themselves. This effective potential can change from a triangular to honeycomb structure depending on the phase of the cavity fields with respect to the laser. We have monitored the dynamics of this system by numerical simulation of the dynamical equations indicating occurrence of superradiance and self-organization of cold atoms in either triangular or honeycomb lattices with equal consecutive or alternative sites, depending on the phase of the cavity fields. The long-time dynamics proves the stability of triangular lattice as well as honeycomb lattice with equal consecutive sites. It is also shown that, in most of the cases, it is possible to drive the system between different lattice structures by dynamically changing the phase of the cavity fields with respect to the laser.

Lieb-Liniger model: emergence of dark solitons in measurements of particle positions
(Andrzej Syrwid, Krzysztof Sacha)
Lieb-Liniger model describes interacting bosons in 1D space. For repulsive particle interactions there are two types of low lying excitation spectrum. The first is reproduced by the Bogoliubov dispersion relation, the other is supposed to correspond to dark soliton excitations. While there are various evidences that the type II spectrum is indeed related to dark soliton states, it has not been shown that measurements of positions of particles reveal dark soliton density profiles. Here, we employ Bethe ansatz approach and show in numerical simulations that dark solitons emerge in the measurement process if the system is prepared in the type II eigenstates.

Tunneling dynamics of bosonic Josephson junctions assisted by a cavity field
(G. Szirmai, G. Mazzarella, L. Salasnich)
We study the interplay between the dynamics of a Bose-Einstein condensate in a double-well potential and that of an optical cavity mode. The cavity field is superimposed to the double-well potential and affects the atomic tunneling processes. The cavity field is driven by a laser red detuned from the bare cavity resonance; the dynamically changing spatial distribution of the atoms can shift the cavity in and out of resonance. At resonance the photon number is hugely enhanced and the atomic tunneling becomes amplified. The Josephson junction equations are revisited and the phase diagram is calculated. We find new solutions with finite imbalance and at the same time a lack of self-trapping solutions due to the emergence of a new separatrix resulting from enhanced tunneling.

Phase separated orbital-FFLO state in a chain of high-spin ultracold atoms
(Edina Szirmai)
Recent experiments with Yb-187 and Sr-87 isotopes [1-3] provides new possibilities to study high-spin two-orbital systems. Within these experiments part of the atoms are excited to a higher energy metastable electronic state providing an additional internal (orbital) degree of freedom [4]. As a consequence of this orbital degree of freedom, the interaction between the atoms is characterized by four independent couplings. Accordingly, when the system is confined into a one-dimensional chain the scatting lengths can be tuned by changing the transverse confinement, and the system can be driven through four resonances. Using the new available experimental data of the scattering lengths we analyse the phase diagram of the one-dimensional system as the couplings are tuned via transverse confinement, and the population of the two orbital states is changed. We found that three orders compete showing power law decay: a state with dominant density wave fluctuation, another one with spin-density fluctuations, and a third one characterized by exotic Fulde-Ferrell-Larkin-Ovchinnikov-like pairs consisting one atom in its electronic ground state and one in the excited state. We also show that sufficiently close to the resonances the compressibility of the system starts to diverge indicating that the emerging order is unstable and collapses to a phase separated state [5]. [1] F. Scazza et al., Nat. Phys. 10, 779 (2014). [2] G. Cappellini et al., Phys. Rev. Lett. 113, 120402 (2014). [3] X. Zhang et al., Science 345, 1467 (2014). [4] A. V. Gorshkov et al., Nat. Phys. 6, 289 (2010). [5] E. Szirmai, Phys. Rev. B 88, 195432 (2013); in preparation (2015).

The Kibble-Zurek mechanism in F=1 antiferromagnetic Bose-Einstein condensates in a harmonic trap
(Tomasz Swislocki, Jacek Dziarmaga, Emilia Witkowska, Michal Matuszewski)
We consider a phase transition from an antiferromagnetic to a phase separated ground state in a spin-1 Bose-Einstein condensate of ultracold atoms in a uniform system and in a harmonic trap. We demonstrate the occurrence of two scaling laws, for the number of spin domain seeds just after the phase transition, and for the number of spin domains in the final, stable configuration in the uniform system. Only the first scaling can be explained by the standard Kibble-Żurek mechanism. Finally we present results for an antiferromagnetic Bose-Einstein condensate in a harmonic trap.

Controlling magnetic Feshbach resonances in polar open-shell molecules with non-resonant light
(Michał Tomza, Rosario Gonzalez-Ferez, Christiane P. Koch, Robert Moszynski)
Magnetically tunable Feshbach resonances for polar paramagnetic ground-state diatomics are too narrow to allow for magnetoassociation starting from trapped, ultracold atoms [1,2]. We show that nonresonant light can be used to engineer the Feshbach resonances in their position and width [3]. For nonresonant field intensities of the order of 10^9 W/cm^2, we find the width to be increased by 3 orders of magnitude, reaching a few Gauss. This opens the way for producing ultracold molecules with sizable electric and magnetic dipole moments and thus for many-body quantum simulations with such particles. [1] Zuchowski et al., Phys. Rev. Lett. 105, 153201 (2010) [2] Brue and Hutson, Phys. Rev. Lett. 108, 043201 (2012) [3] Tomza et al., Phys. Rev. Lett. 112, 113201 (2014)

Two-Component Fermi Gases with Contact Interaction
(Martin-I. Trappe, Miroslaw Brewczyk, and Kazimierz Rzazewski)
In the light of recent experimental efforts we investigate two-component atomic Fermi gases with repulsive contact interaction. Our objective is the time evolution of two such interacting Fermi gases that collide in confining traps. We prove that the standard way of obtaining approximate ground-state particle densities via the extrema of the Thomas-Fermi equations only yields solutions with equal densities if we demand equal particle numbers for both atomic species. This shortcoming of the Thomas-Fermi equations, connected to the finite support of the Thomas-Fermi solutions, is observed for all dimensions and isotropic potentials that are monotonously increasing with radius. We propose to obtain viable ground state densities from an imaginary-time evolution of a Schr\"odinger-like equation that is calculated from Madelung's hydrodynamic formulation of quantum mechanics. With this approach we can conveniently include gradient corrections to the Thomas-Fermi approximation.

Large-scale simulations with tensor networks
(Miroslav Urbanek, Pavel Soldán)
Simulations based on tensor networks have recently become a popular tool in computational quantum physics. They are especially useful for studying time evolution in one-dimensional lattice models. Not all models are accessible to numerical study, because entanglement can build up quickly in large systems with many particles. This results in high computer memory requirements. In this talk, I will discuss strategies for parallel implementation of tensor network algorithms on distributed-memory architectures. I will present TEBDOL [1], a program using parallel version of the Time-Evolving Block Decimation algorithm to simulate large-scale one-dimensional systems of ultracold atoms in optical lattices. Its good strong- and weak-scaling performance on supercomputer clusters allows us to investigate complex models. The program was recently used in a study of binary mixtures in an optical lattice [2]. [1] M. Urbanek and P. Soldán, Comput. Phys. Commun., submitted (2015). [2] M. Urbanek and P. Soldán, Phys. Rev. A 90, 033610 (2014).

Interferometry with independently prepared Bose-Einstein condensates
(T. Wasak, P. Szankowski, J. Chwedenczuk)
The value of an unknown parameter estmated from a series of experiments is inevitably burdened by the uncertainty. If the system, which is the subject of measurement, consists of classically correlated particles, this uncertainty is bounded by the shot-noise limit. To overcome this limitation, it is necessary to use an entangled state, which is usually prepared in a dedicated procedure. In this talk, it is shown that quantum correlations arising from the indistinguishability of bosons are a sufficient resource for the sub-shot-noise interferometry. To this end, an interferometer is considered, which operates on two independently prepared Bose-Einstein condensates with fluctuating numbers of particles. The sensitivity obtained from the measurement of the number of atoms is compared with the ultimate achievable bound. The main conclusion is that even in presence of major atom number fluctuations, an interferometer operating on two independently prepared condensates can give very high precision.

From dynamics of a single superfluid vortex to quantum turbulence in the unitary Fermi gas: results of time-dependent superfluid density functional theory
(G. Wlazłowski, A. Bulgac, M.M. Forbes, K.J. Roche)
Quantized vortices are a hallmark of superfluids. Their generation, dynamics, evolution, and eventual decay have been studied experimentally for some six decades in liquid He and recently in Bose and Fermi cold atom systems. While life cycle of quantized vortices in Bose systems can be described by simple Gross-Pitaevskii equation, Fermi systems are more demanding where satisfactory description requires inclusion of many mechanisms for superfluid relaxation like various phonon processes or Cooper pair breaking. In this talk I will show that time-dependent superfluid density functional theory (TDDFT) in natural manner incorporates all these necessary ingredients. I will present numerical results for formation and dynamics of a superfluid vortex in the unitary Fermi gas and I will compare them with recent MIT experimental observations. Moreover, I will demonstrate how various vortex configurations, including quantum turbulent state, can be generated by using well established experimental techniques: laser stirring and phase imprinting.

Classical and Quantum simulations of coupled quantum fields
(Fernando Quijandría, Juanjo García-Ripoll, David Zueco)
I will review our recent work on the ground state calculation for (non relativistic) coupled quantum fields based on continuous Matrix Product States (cMPS) [1]. The cMPS is a variational ansatz for the ground state of quantum field theories in one dimension. Our method will be applied to coupled atomic interacting gases. In particular, I will characterize the low-Energy effective theory and discuss the emergence of a global Lorentz Invariant symmetry. I will also report on different phases transitions in the coupled model. The cMPS theory is based on a mapping between the fields and zero-dimensional open systems (ancillas obeying a Lindblad equation). This physical point of view permits a new paradigm on the quantum simulation for fields, complementary to analogic or digital simulations. The idea is, instead the fields, to simulate the ancillas. In the talk, I will propose a quantum simulator of a phase transition in quantum fields within circuit QED architectures. I will finish by tracking the phase transition within the ancilla parameters.