Quantum Technologies Conference VII

Manipulating photons, atoms, and molecules

September 20 - 25, 2016
Warszawa, Poland


Invited talks

1. Molte Andersen
      Aarhus University (Denmark)
An interpolatory ansatz captures the physics of one-dimensional confined Fermi systems
(M.E.S. Andersen, A. S. Dehkharghani, A. G. Volosniev, E. J. Lindgren, N. T. Zinner)
Interacting one-dimensional quantum systems play a special role among few- and many-body models as exact solutions can be obtained for the homogenous case using the Bethe ansatz and bosonisation techniques. Unfortunately, these approaches are not applicable when external confinement is present unless some variation of the local density approximation is employed. Recent theoretical advances beyond the Bethe ansatz and bosonisation allow us to predict the behaviour of one-dimensional confined quantum systems with strong short-range interactions, and new experiments with cold atomic Fermi gases have already confirmed these theories. Here we demonstrate that a simple linear combination of the strongly interacting solution with the well-known solution in the limit of vanishing interactions provides a simple and accurate description of the system for all values of the interaction strength. This indicates that one can indeed capture the physics of confined one-dimensional systems by knowledge of the limits using wave functions that are much easier to handle than the output of typical numerical approaches. We demonstrate our scheme for experimentally relevant systems with up to six particles. Moreover, we show that our method works also in the case of mixed systems of particles with different masses. This is an important feature because these systems are known to be non-integrable and thus not solvable by the Bethe ansatz technique.

2. Tomas Andrijauskas
      Vilnius University (Lithuania)
Topological properties of optical flux lattice created with multi-frequency radiation
(Tomas Andrijauskas, Ian B. Spielman, Gediminas Juzeliunas)
Ultracold atomic gases are systems exhibiting various condensed matter phenomena. Possible ways to create artificial magnetic field for ultracold atoms include rotation of an atomic cloud, laser-assisted tunnelling and shaking of optical lattices. We theoretically describe another way of creating a non-staggered magnetic flux for ultra-cold atoms by using a periodic sequence of short laser pulses providing a multi-frequency perturbation. We consider a possibility to create a square flux lattice for ultra-cold atoms characterized by two internal states. The magnetic gradient, which splits the levels in one direction, and the multi-frequency coupling in the perpendicular direction effectively creates a square optical lattice affected by a non-staggered magnetic flux. We explore the band structure of such flux lattice and its topological properties. We show that in the adiabatic regime few of the lowest energy bands contain Chern numbers all equal to one and resemble Landau levels.

3. Egidijus Anisimovas
      Vilnius University (Lithuania)
Micromotion-induced interactions in a Floquet topological system and the stability of fractional Chern insulating states
(Egidijus Anisimovas, Mantas Raciunas, Giedrius Zlabys, Andre Eckardt)
The main focus of this talk is the interplay of particle interactions and micromotion in a periodically driven optical lattice that supports a topologically nontrivial quasienergy band structure and thus may host fractional Chern insulating states. To set the stage, we will first present a simple scheme for the realization of a topological band structure in a driven optical square lattice. The scheme is based on a circular lattice shaking in the presence of a superlattice that lowers the energy on every other site in a checkerboard pattern. The topological band gap, which separates the two bands with Chern numbers plus or minus one, is opened in a way characteristic of Floquet topological insulators, that is, by terms of the effective Hamiltonian that appear in subleading order of a high-frequency expansion. These terms can be interpreted as processes where a particle tunnels several times during one driving period. The interplay of such processes with particle interactions gives rise to new interaction terms of several distinct types. For bosonic atoms with on-site interactions, the additional interaction terms include nearest-neighbor density-density interactions introduced at the cost of weakened on-site repulsion as well as density-assisted tunneling. Using exact diagonalization, we investigate the impact of the individual induced interaction terms on the stability of a bosonic fractional Chern insulator state at half filling of the lowest band.

4. Jogundas Armaitis
      Vilnius university (Lithuania)
Superfluidity and spin superfluidity in spinor Bose gases
(J. Armaitis & R. A. Duine)
We investigate the interplay between superfluidity and spin superfluidity in spinor Bose gases with easy-plane anisotropy. To illustrate that the basic principles governing these two types of superfluidity are the same, we describe the magnetization and particle-density dynamics in a single hydrodynamic framework. In this description spin and mass supercurrents are driven by their respective chemical potential gradients. As an application, we propose an experimentally-accessible stationary state, where the two types of supercurrents counterflow and cancel each other, thus resulting in no mass transport. Furthermore, we propose a straightforward setup to probe spin superfluidity by measuring the in-plane magnetization angle of the whole cloud of atoms. We verify the robustness of these findings by evaluating the four-magnon collision time, and find that the timescale for coherent (superfluid) dynamics is separated from that of the slower incoherent dynamics by one order of magnitude. Comparing the atom and magnon kinetics reveals that while the former can be hydrodynamic, the latter is typically collisionless under most experimental conditions. This implies that, while our zero-temperature hydrodynamic equations are a valid description of spin transport in Bose gases, a hydrodynamic description that treats both mass and spin transport at finite temperatures may not be readily feasible. Reference: arXiv:1603.01996 .

5. Remigiusz Augusiak
      Center for Theoretical Physics PAS (Poland)
Random bosonic states for robust quantum metrology
(M. Oszmaniec, R. Augusiak, C. Gogolin, J. Kołodyński, A. Acín, M. Lewenstein)
We study how useful random states are for quantum metrology, i.e., surpass the classical limits imposed on precision in the canonical phase estimation scenario. First, we prove that random pure states drawn from the Hilbert space of distinguishable particles typically do not lead to super-classical scaling of precision even when allowing for local unitary optimization. Conversely, we show that random states from the symmetric subspace typically achieve the optimal Heisenberg scaling without the need for local unitary optimization. Surprisingly, the Heisenberg scaling is observed for states of arbitrarily low purity and preserved under finite particle losses. Moreover, we prove that for such states a standard photon-counting interferometric measurement suffices to typically achieve the Heisenberg scaling of precision for all possible values of the phase at the same time. Finally, we demonstrate that metrologically useful states can be prepared with short random optical circuits generated from three types of beam-splitters and a non-linear (Kerr-like) transformation.

6. Michal Bialonczyk
      Atomic Optics Department, Marian Smoluchowski Institute of Physics, Jagiellonian University in Kraków (Poland)
Spectral properties of quantum channels - a glimpse from the algebraic point of view
(Michal Bialonczyk)
Spectral properties of a quantum channel are important e.g. in the case when one considers the iterative dynamics of the open quantum system. Every quantum channel is defined by the corresponding set of Kraus operators, from which we can generate an algebra. We show, how one can, using only algebraic properties of the set of Kraus operators deduce the possible form of all the eigenvalues of the modulus one for unital quantum channel. We provide the particular examples for three, four and five - level quantum systems.

7. Iwo Białynicki-Birula
      Centrum Fizyki Teoretycznej PAN ()
Manipulating neutral atoms endowed with magnetic moments
(Iwo Bialynicki-Birula and Tomasz Radożycki)
The motion of a neutral atom endowed with a magnetic moment interacting with the magnetic field is determined from the Ehrenfest-like equations of motion. These equations for the average values of the translational and spin degrees of freedom are derived from the Schroedinger-Pauli wave equation and they form a set of nine coupled nonlinear evolution equations. The numerical and analytic solutions of these equations are obtained for the combination of the rotating magnetic field of a wave carrying orbital angular momentum and a static magnetic field. The running wave traps the atom only in the transverse direction while the standing wave traps the atom also in the direction of the beam.

8. Krzysztof Biedroń
      Uniwersytet Jagielloński (Poland)
Exact diagonalization studies of a shaken lattice with an emergent, nontrivial topology
(Krzysztof Biedroń, Omjyoti Dutta, Jakub Zakrzewski)
In a recent proposal it is suggested that using lattice shaking in a 1D optical lattice allows one to create system, in which defects behave as topologically protected quasiparticles [1]. In my talk I would like to present the results of exact diagonalization calculations which support that claim and provide further insight into the system properties [2]. [1] Anna Przysiężna, Omjyoti Dutta, and Jakub Zakrzewski. "Rice–Mele model with topological solitons in an optical lattice." New Journal of Physics 17.1 (2015): 013018. [2] Krzysztof Biedroń Omjyoti Dutta, and Jakub Zakrzewski. "Topological Rice-Mele model in an emergent lattice: Exact diagonalization approach." Phys. Rev. A 93, 033631 (2016)

9. Denis Boiron
      Institut d`Optique (France)
Atomic Hong-Ou-Mandel experiment
(P. Dussarrat, M. Perrier, R. Lopes, A. Imanaliev, A. Aspect, M. Cheneau, D. Boiron, C. I. Westbrook)
Two-particle interference is a fundamental feature of quantum mechanics. The experiment performed with photons by Hong,Ou and Mandel in 1987 was a simple yet striking effect of such an interference where two indistinguishable photons impinging each on a different port of a beam-splitter always emerge in the same output port. We report an atomic analogue of this experiment using pairs of atoms produced by dynamical instability in an optical lattice and manipulated by two-photon Bragg diffraction to simulate mirror and beam-splitter. Thanks to our single atom and momentum-resolved detector of metastable helium atoms, we were able to demonstrate the quantum nature of the two-particle interference looking at coincidence counts at the two output port of the beam-splitter.

10. Marie Bonneau
      Atominstitut, TU Wien (Austria)
Relaxation of a 1D Bose gas prepared in a vibrational levels superposition
(Marie Bonneau, Sandrine van Frank, Mira Maiwöger, Raisa Trubko, Marine Pigneur, RuGway Wu, Thorsten Schumm, Jörg Schmiedmayer )
Understanding the non-equilibrium dynamics of quantum many-body systems is an open problem, common to systems with very different length, time and energy scales, ranging from cosmology to ultracold gases. We consider here the relaxation dynamics of a 1D Bose gas prepared in a coherent superposition of the first two transverse vibrational levels of the trapping potential. The system is initialized through optimal control of the displacement of the anharmonic transverse potential [1]. This method permits fast preparation of excited motional states with 99% fidelity and is robust towards atom number fluctuations [2]. Experimental characterization of the non-equilibrium evolution was performed. The system evolves towards a steady state, with a characteristic timescale strongly depending on the atom number of the Bose gas. We investigated the contribution to the relaxation of several effects: Local fluctuations of the vibrational levels’ relative population arise during the system initialization, leading to prethermalization through propagation of relative density and relative phase excitations, in a similar fashion as observed for symmetrically split 1D gases [3]. Another source of longitudinal dephasing is the finite longitudinal coherence of the 1D gas, which results in fluctuations of the relative phase due to the asymmetry of the levels’ sound velocities. Additionally, emission of atom pairs from the excited vibrational level [4] triggers many-body dephasing. [1] van Frank et al., Nat. Commun. 5, 4009 (2014). [2] van Frank et al., arXiv:1511.02247 (2015). [3] Gring et al, Science 337, 1318 (2012). [4] Bücker et al., Nat. Phys. 7, 608–611 (2011).

11. Luis A. Correa
      The University of Nottingham (United Kingdom)
High-precision low-temperature quantum thermometry
(Luis A. Correa)
The problem of estimating the temperature T of an equilibrium sample is normally tackled by coupling it weakly to a probe. Once joint thermal equilibrium has been reached, one may estimate the temperature of the sample from the results of measurements performed on the probe. Provided that this is small (in the limit, just an individual quantum system), it is usually assumed that the back-action on the sample is negligible, and that the probe ends up in a Gibbs state at temperature T. This simple picture runs into trouble when the temperature of the sample is low enough: On the one hand, the thermal sensitivity of an equilibrium probe vanishes exponentially as the temperature decreases. On the other hand, at low temperatures, sample and probe may build correlations, which eventually pushes the state of the latter away from equilibrium. In this talk we will discuss in depth the design optimization of nanoscale probes for practical low-temperature thermometry.

12. Charles Creffield
      Universidad Complutense de Madrid (Spain)
Realizing uniform synthetic magnetic fields by periodically shaking an optical lattice
(C.E. Creffield, G. Pieplow, N. Goldman, and F. Sols)
Shaking a lattice system, by modulating the location of its sites periodically in time, is a powerful method to create synthetic magnetic fields in engineered quantum systems, such as cold gases trapped in optical lattices. However, such schemes are typically associated with either space-dependent effective masses (tunneling amplitudes) or non-uniform flux distributions. We investigate this phenomenon by computing the effective Hamiltonians and the Floquet quasienergy spectra associated with a family of shaken lattice systems. This allows us to identify novel shaking schemes which simultaneously provide uniform effective mass and homogeneous magnetic flux, with direct implications for cold-atom experiments and photonics.

13. Piotr Czarnik
      Jagiellonian University (Poland)
Variational Tensor Network Renormalization in Imaginary Time.
(P. Czarnik, M. Rams and J. Dziarmaga)
The Gibbs operator $e^{−eta H}$ for a two-dimensional (2D) lattice system with a Hamiltonian H can be represented by a three-dimensional tensor network, the third dimension being the imaginary time (inverse temperature) $eta$. Coarse-graining the network along $beta$ results in a 2D projected entangled-pair operator (PEPO) with a finite bond dimension D. The coarse-graining is performed by a tree tensor network of isometries. The isometries are optimized variationally --- taking into account full tensor environment --- to maximize the accuracy of the PEPO. The algorithm is applied to the isotropic quantum compass model on an infinite square lattice near a symmetry-breaking phase transition at finite temperature. From the linear susceptibility in the symmetric phase and the order parameter in the symmetry-broken phase the critical temperature is estimated at $T_c=0.0606(4)J$, where J is the isotropic coupling constant between S=1/2 pseudospins. The algorithm is also applied to the two-dimensional Hubbard model on an infinite square lattice. Benchmark results are obtained that are consistent with the best dynamical mean field theory (DCA - dynamical cluster approximation) and power series expansion (NLCE - numerically linked cluster expansion) in the regime of parameters where these more conventional methods yield mutually consistent results. [1] P.Czarnik, J.Dziarmaga; Phys. Rev. B 92, 035152 (2015). [2] P.Czarnik, J.Dziarmaga, A.M.Ole's; Phys. Rev. B 93, 184410 (2016). [3] P.Czarnik, M. Rams, J.Dziarmaga; in preparation.

14. Bryan Dalton
      Swinburne University of Technology (Australia)
Tests for EPR Steering in Systems of Identical Bosons
(B J Dalton and M D Reid)
*In previous work [1-2] quantum entanglement was treated for identical particle systems based on requiring the density operator to comply with the symmetrisation principle (SP) and with super-selection rules (SSR) prohibiting states with coherences between differing total particle numbers. The subsystems are distinguishable modes, the subsystem density operators for separable states also satisfying the SP and SSR for subsystem particle numbers. Spin squeezing in any spin component and a weak correlation test were shown to be new sufficiency tests for two mode entanglement with massive bosons. Other spin squeezing related tests for two-mode entanglement, such as the sum of Sx, Sy spin operator variances being less than half the mean boson number [3] and strong correlation tests also applied. *Quantum states for composite systems are categorised as either separable or entangled, but the states can also be divided differently into Bell local or Bell non-local states. The latter categorisation is based on whether or not the probability P(a,b|A,B,c) for measured outcomes a,b on sub-system observables A,B for state preparation process c, is given by a local hidden variable theory (LHVT) form P(a,b|A,B,c) = Sum-h {p(a|A,c,h) p(b|B,c,h) p(h|c)} (where preparation c results in a probability distribution p(h|c) for hidden variables h, p(aA,c,h) is the probability for measured outcome a on sub-system observable A when the hidden variables are h, with p(b|B,c,h) the analogous observable B probability). Quantum states where P(a,b|A,B,c) is given by a LHVT form are Bell local, if not they are Bell non-local and associated with Bell inequality violation experiments. As well as the separable states, some entangled states are Bell local [4], though all Bell non-local states are entangled. *For the Bell local states there are three cases depending on whether both, one of or neither of the LHVT probabilities p(a|A,c,h) and p(b|B,c,h) are also given by a quantum probability involving sub-system density operators. Cases where one or both are given by a quantum probability are known as local hidden states (LHS) and such states are non-EPR steerable [5-6]. All separable states are LHS, but some LHS are entangled. *We find that spin squeezing in the Sz spin component and a weak correlation test show that the LHS model fails (including for the non-separable case) - hence the quantum state is EPR steerable. Tests via spin squeezing in other spin components are not tests for EPR steering, but the Hillery spin variance test [3] applies. A stronger version of the latter EPR steering test based on [7] and involving as well as is also found to apply. * Refeences. [1] B J Dalton, L Heaney, J Goold, B M Garraway & Th Busch, New J Phys 16, 013026 (2014) [2] B J Dalton, J Goold , B M Garraway & M D Reid, ArXiv Quant-ph, 1506.06906, 1506.06892 (2016) [3] M Hillery & M S Zubairy, Phys Rev Letts 96, 050503 (2006) [4] RF Werner, Phys Rev A 40, 4277 (1989) [5] H W Wiseman, S J Jones & A C Doherty, Phys Rev Letts 98, 140402 (2007), Phys Rev A 76, 052116 (2007) [6] E G Cavalcanti, S J Jones, H W Wiseman & M D Reid, Phys Rev A 80, 032112 (2009) [7] Q Y He, P D Drummond, M K Olsen & M D Reid, Phys Rev A 86, 023626 (2012)

15. Bogdan Damski
      Jagiellonian University (Poland)
Locating quantum critical points through singularities of simple observables
(Bogdan Damski)
Quantum critical points are traditionally associated with non-analyticity of the ground state energy reflecting fundamental differences between phases of a system undergoing a quantum phase transition. We discuss how this non-analyticity is passed onto ground state expectation values of different terms of the Hamiltonian. We illustrate our results in the two-dimensional Bose-Hubbard model that can be realized in cold atomic systems. Using quantum Monte Carlo simulations, we show that one can easily extract the position of the critical point in this model from the on-site atom number fluctuations and nearest-neighbor tunnelling. Our results provide a simple experimentallyrelevant way of locating critical points in numerous systems undergoing a quantum phase transition.

16. Alexandre Dauphin
      ICFO (Spain)
Quantum simulation of a topological Mott insulator with Rydberg atoms in a Lieb lattice
(A. Dauphin, M.Muller and M. A. Martin-Delgado)
Topological insulators have attracted much interest in the last decades. These exotic phases are characterized by a global topological invariant, going beyond the Landau theory of phase transitions, and have robust carrying surface states protected by the topology of the band. Quantum simulation offers new possibilities to simulate such phases. We here focus on quantum simulation of the so-far experimentally unobserved topological Mott insulator, where topology arises dynamically from interactions and this, without any background gauge field. To this end, we study a model of spinless fermions on a Lieb lattice with nearest and next-to-nearest neighbor hopping, discuss the mean field phase diagram. In particular, we characterize the topology of the different phases and show that a quantum anomalous Hall phase can arise from interactions. Finally, we propose a realistic implementation of this model using cold Rydberg dressed atoms in an optical lattice. A. Dauphin, M.Muller and M. A. Martin-Delgado, Phys. Rev. A 93, 043611 (2016)

17. Michał Dąbrowski
      University of Warsaw, Faculty of Physics (Poland)
Enhanced-Rate Generation of Photons using High-Capacity Angularly-Multiplexed Holographic Memory
(Michał Dąbrowski, Radosław Chrapkiewicz, Wojciech Wasilewski)
We experimentally demonstrate [1] an angularly-multiplexed holographic memory capable of intrinsic generation, storage and retrieval of photons, based on off-resonant Raman interaction in warm rubidium-87 vapors. The memory capacity of up to 60 independent atomic spin-wave modes is evidenced by analyzing angular distributions of coincidences between Stokes and time-delayed anti-Stokes photons, observed down to the single spin wave excitation level. We also show how to practically enhance rates of single and multiple photons generation by combining our multimode emissive memory with existing optical switches reconfigurable much faster than the memory several microsecond-lifetime. [1] R. Chrapkiewicz, M. Dąbrowski, and W. Wasilewski, arXiv:1604.06049

18. Maciej Demianowicz
      Politechnika Gdańska (Polska)
Entanglement and nonlocality are inequivalent for any number of particles
(R. Augusiak, M. Demianowicz, J. Tura, A. Acin)
Understanding the relation between nonlocality and entanglement is one of the fundamental problems in quantum physics. In the bipartite case, it is known that the correlations observed for some entangled quantum states can be explained within the framework of local models, thus proving that these resources are inequivalent in this scenario. However, except for a single example of an entangled three-qubit state that has a local model, almost nothing is known about such relation in multipartite systems. We provide a general construction of genuinely multipartite entangled states that do not display genuinely multipartite nonlocality, thus proving that entanglement and nonlocality are inequivalent for any number of particles. The relation between steering and entanglement is also discussed.

19. Piotr Deuar
      IFPAN (Poland)
The behaviour of superfluid defects in condensates during time-of flight expansion
(Piotr Deuar)
Images of superfluid defects in an ultracold atom cloud such as solitons and vortices are usually made after a large expansion of the cloud, but one that has not yet reached the velocity distributed far field. However, they undergo significant distortion and rearrangement during this expansion phase. This can be helpful (they broaden to available resolutions) or harmful (they are distorted or overlap). Such free-flight dynamics has been relatively poorly investigated because of the technical difficulty of simulating large-scale expansions, particularly in three dimensions. This is the "disaster of changing scales". We have developed an algorithm that allows one to sidestep this disaster and obtain exact densities after a large-scale free-flight expansion of the wavefunction. This has allowed us to track the expansion to realistically large expansion ratios of tens or more, and I will present some pertinent observations on the physics and relevant timescales.

20. Tanja Duric
      Jagiellonian University (Poland)
Fibonacci anyon excitations of one-dimensional dipolar lattice bosons
(Tanja Duric, Krzysztof Biedron, Jakub Zakrzewski)
We study a system of dipolar bosons in a one-dimensional optical lattice using exact diagonalization and density matrix renormalization group methods. In particular, we analyze low energy properties of the system at an average filling of 3/2 atoms per lattice site. Contrary to previous calculations, our results demonstrate that super-solid phases are not present in the phase diagram. Instead, decreasing the value of the nearest-neighbor tunneling strength leads to a direct super-fluid to charge-density-wave second-order quantum phase transition. We also identify the region of the parameter space where the system has non-Abelian Fibonacci anyon excitations. When such one-dimensional systems are combined into a two-dimensional network, braiding of Fibonacci anyon excitations has potential application for fault tolerant, universal, topological quantum computation.

21. Anna Francuz
      Jagiellonian University (Polska)
Evidence for Kibble-Zurek scaling hypothesis
(Anna Francuz, Jacek Dziarmaga, Bartłomiej Gardas, Wojciech H. Żurek)
The evolution of a quantum system that is driven across the quantum critical point at a constant rate becomes nonadiabatic due to the critical slowing down. Good description of such dynamical quantum phase transitions is provided by Kibble-Zurek mechanism. It states that the system after the transition is in the excited state, imprinted with characteristic time and length scales depending on the transition rate. This suggests scaling behaviour in both space and time. The evidence for spatial and temporal scaling is provided both by an exact solution of the quantum Ising chain and the recent Chicago experiment with Bose-Einstein condensates.

22. Krzysztof Giergiel
      Jagiellonian University in Krakow (Poland)
Anderson localization in the time domain
(Krzysztof Giergiel and Krzysztof Sacha)
Recently Anderson localization in the time domain has been demonstrated in systems that reveal non-spreading wave-packets dynamics.Here we show that Anderson localization in time is a more general phenomenon and does not require preparation of non-spreading wave-packets. Temporally disordered driving of a quantum system can lead to Anderson localization of a particle along an unperturbed periodic trajectory. Experimentally it can be realized in, e.g., ultra-cold gases, condensed matter systems and Rydberg atoms. We illustrate Anderson localization in time with the help of Rydberg atoms driven by a temporally disordered microwave field. System is investigated numerically and by means of an effective hamiltonian within the secular perturbation theory.

23. Wojciech Gorecki
      Center for Theoretical Physics, Polish Academy of Sciences (Poland)
Two dipolar atoms in a harmonic trap
(Rafał Ołdziejewski, Wojciech Górecki and Kazimierz Rzążewski)
Two identical dipolar atoms moving in a harmonic trap without an external magnetic field are investigated. Using the algebra of angular momentum we reduce the problem to a simple numerics. We show that the internal spin-spin interactions between the atoms couple to the orbital angular momentum causing an analogue of Einstein-de Haas effect. We show a possibility of adiabatically pumping our system from the s-wave to the d-wave relative motion. The effective spin-orbit coupling occurs at anti-crossings of the energy levels.

24. Benoit Gremaud
      Laboratoire Kastler Brossel / Centre for Quantum Technologies (France / Singapore)
Excitation and dynamics in the extended bose-hubbard model
(Benoit Gremaud and George Batrouni)
Using the time evolving block decimation method, we study the excitation spectrum above the ground state of the one dimensional extended Bose Hubbard model in different phases. First, at unit filling, we discuss the properties of the structure factor across the Mott insulating phase, the Haldane insulating phase and the charge density wave phase. In particular, in the Haldane phase, we emphasize the competition between the single particle and two particle excitations, resulting in different values for the neutral and the charge gap. In the supersolid phase appearing by doping the charge density wave phase, we find that the structure factor depicts additional gapless modes at a finite momentum that depends on the density. This feature and the low energy spectrum can be explained by a mapping of the system onto the Heisenberg model for a spin 1/2 chain in a finite magnetic field.

25. Krzysztof Jachymski
      University of Stuttgart (Germany)
Prospects for ultracold atom-ion scattering
(Krzysztof Jachymski, Michał Tomza, Michal Tarana, Thomas Schmid, Christian Veit, Robert Loew, Tilman Pfau)
We propose a new experimental scheme to extend the investigation of ion-atom collisions to the ultracold, quantum regime. Reaching the quantum scattering regime can be made possible by the use of an ion-atom system with a small reduced mass and by employing a specific type of a heteronuclear D-state Rydberg molecule to initialize the scattering event. For the suggested 87Rb+ - 6Li system, we present quantum mechanical calculations of the elastic total and differential scattering cross section which will both be measurable in the proposed experiment. We discuss the possibility of associating weakly bound ultracold molecular ions using Feshbach resonances and photoassociation. These molecules would have remarkable properties such as extremely large dipole moment.

26. Aisling Johnson
      Laboratoire Charles Fabry, Institut d`Optique (France)
Dissipative cooling in one-dimensional Bose Gases: classical field and quantum Monte Carlo studies
(Aisling Johnson, Raphaël Photopoulos, Maximilian Schemmer, Isabelle Bouchoule)
In one-dimensional systems, evaporative cooling is inefficient because of the lack of thermalising collisions. Recently, a dissipative mechanism was proposed and experimentally implemented in one-dimensional Bose gases [1,2]. Based on non-selective atom loss in the gas, it leads to effective temperatures lower than those accessible with usual evaporation, an efficiency inherent to the integrability of the 1D Bose gas. We report on a classical field simulation of this dissipative mechanism. We show that this process leads to a non-equilibrium state where energy is not equally distributed in the Bogoliubov modes, and relate this result to experimental observations. We also developed a linearised quantum Monte Carlo approach (each mode evolving independently) to include quantum fluctuations which add noise and limit the cooling to a non-vanishing asymptotic temperature [1]. As an atom is lost and detected this affects the Wigner function of an individual mode. After averaging ! over quantum trajectories, we recover the results of [1]. Finally, this approach allows to implement a quantum feedback method to cool beyond the quantum fluctuation limit. [1] Grisins et al, PRA, 2016 [2] Rauer et al, PRL, 2016

27. Arkadiusz Kosior
      Jagiellonian University (Poland)
Localization in random fractal lattices
(Arkadiusz Kosior, Krzysztof Sacha)
We investigate the issue of eigenfunction localization in random fractal lattices embedded in two dimensional Euclidean space. In the system of our interest, there is no diagonal disorder - the disorder arises from random connectivity of lattice sites only. By adding/removing links between lattice sites, we change the spectral dimension of a lattice but keep the fractional Hausdorff dimension fixed. From the analysis of energy level statistics obtained via direct diagonalization of finite systems, we observe localization-delocalization transition. In addition, for low spectral dimensions $d_sapprox1.3$, we observe superlocalization resonances and a formation of an energy gap around band center.

28. Mateusz Lacki
      Institute for Theoretical Physics, University of Innsbruck, and Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences (Austria)
A ‘dark state’ optical lattice for cold atoms
(Mateusz Lacki, Mikhail Baranov, Hannes Pichler, and Peter Zoller)
We describe a new way to construct an optical lattice. In the standard setting one uses a a second order process, an AC Stark shift from a far-detuned excited state. The new way is based on different paradigm: a position-dependent dark state generated by a Lambda-type resonant coupling with Raman-type standing wave beams. An atom in the dark state feels an effective potential which is a comb of Dirac-delta like potentials, with distinctively sub-wavelength width. The setup allows for including of the spin-orbit coupling. We present a detailed single-particle description of the model such as band structure, but also discuss in detail losses due to violation of the adiabatic condition and coupling by motion between the dark and bright states and resulting spontaneous emission. Finally, we show the extension to the many-body case where the atoms carry an dipolar moment, which leads to a situation where the inter-atom interaction is modulated in space, and the also-present single particle potential is relatively weaker. This allows of creation of "domain wall molecules" of subwavelength extent and construction of unconventional Hubbard models.

29. Wieslaw Laskowski
      University of Gdansk (Polska)
Local random unitary noise for multipartite quantum states
(Marcin Markiewisz, W. Laskowski, Z. Puchala, A. de Rosier, Karol Zyczkowski)
Quantum Fisher Information (QFI), which was originally developed as a mean to quantify the efficiency of parameter estimation, was further applied to quantify performance of some information processing tasks, like imperfect quantum cloning, adjusting reference frames and quantum search. In this work we apply QFI to the problem of bounding the fidelity of a multipartite quantum state undergoing collective unitary noise. The key idea is that optimizing QFI over different directions corresponding to generators of a unitary group in case of qubits is very simple. We generalize this idea to the case of arbitrary finite dimension, and show, how this new property of QFI allows one to assess the fidelity.

30. Grzegorz Litak
      Lublin University of Technology (Poland)
Instability of a Bose-Einstein condensate on an optical lattice potential by Melnikov approach
(Grzegorz Litak, Krzysztof Urbanowicz)
Particle number density and phase of a Bose-Einstein condensate (BEC) with attractive inter-atomic interaction on the optical lattice are considered. We start from the time dependent Gross-Pitaevskii equation, which governs the dynamics of the BEC system in mean-field theory. We consider a damped BEC loaded into a traveling optical lattice. The damping effect is caused by the incoherent exchange of normal atoms and the finite temperature. Under a deterministic and stochastic perturbation the corresponding solution instability is studied by the Melnikov criterion.

31. Niels Jakob Søe Loft
      Department of Physics and Astronomy, Aarhus University (Denmark)
Engineering spin chains using strongly interacting cold atoms
(Loft, N.J.S. et al.)
Physicists today are able to manipulate cold atoms in optical traps to such a degree of accuracy that a lot of interesting models can be simulated. Specifically, it is possible to realize the Heisenberg spin chain model using cold strongly interacting atoms in a one-dimensional trap. By tuning the geometry of the trap, it is possible to engineer the local exchange coefficients and obtain self-assembled spin chain Hamiltonians. We have developed an efficient computational method that provides the link between the geometry of the confining trap and the spin chain Hamiltonian. We suggest that our method can be used as a powerful theoretical tool for realizing many spin chain models with cold trapped atomic gases.

32. Jan Major
      Uniwersytet Jagiellonski (Polska)
Delocalized modes in 1D optical lattice with randomly distributed generalized N-mers.
(Jan Major)
In one dimensional lattice systems in presence of disorder all states are localized unless the disorder is correlated. We propose analytical method applicable for specific types of correlations, that gives positions of such resonances . As an example, we apply it to randomly distributed generalized N-mers -- systems which are realizable experimentally and can posses several delocalized states with tunable energies.

33. Mohammad Mehboudi
      Física Teòrica: Informació i Fenòmens Quàntics, UAB, Barcelona (Spain)
Parameter estimation and the dynamics of open quantum systems
(Mohammad Mehboudi, Luis. A. Correa, Juan M.R. Parrondo, Anna Sanpera)
Once at thermal equilibrium, we study the estimation of temperature and internal parameters of a quantum system. We explain the roots of the appearance of connections between the precision of estimating such parameters and well-known quantities in thermodynamics such as heat capacity and magnetic susceptibility. Further we quantify how the non-commutative algebra, between different terms of a given Hamiltonian, enhances or worsens the accuracy of parameter estimation. Beyond the thermal equilibrium, we also explore the parameter estimation in models which are perturbed slightly from their equilibrium state, either by changing an internal parameter of the system or by manipulating its environment. We retrieve the same connection, between the precision of parameter estimation and the extit{extended susceptibilities}. We present several examples to make our results more clear.

34. Antonio Negretti
      Zentrum für Optische Quantentechnologien, Universität Hamburg (Germany)
Controlled long-range interactions between Rydberg atoms and ions
(Thomas Secker, Rene Gerritsma, Alexander W. Glaetzle, Antonio Negretti)
We theoretically investigate trapped ions interacting with atoms that are coupled to Rydberg states. The strong polarizabilities of the Rydberg levels increases the interaction strength between atoms and ions by many orders of magnitude, as compared to the case of ground state atoms, and may be mediated over micrometers. We calculate that such interactions can be used to generate entanglement between an atom and the motion or internal state of an ion. Furthermore, the ion could be used as a bus for mediating spin-spin interactions between atomic spins in analogy to much employed techniques in ion trap quantum simulation. The proposed scheme comes with attractive features as it maps the benefits of the trapped ion quantum system onto the atomic one without obviously impeding its intrinsic scalability. No ground state cooling of the ion or atom is required and the setup allows for full dynamical control. Moreover, the scheme is to a large extent immune to the micromotion of the ion. Our findings are of interest for developing hybrid quantum information platforms and for implementing quantum simulations of solid state physics.

35. Michal Oszmaniec
      ICFO (Spain)
Measuring the magnetic-field gradient using the decoherence-free subspaces
(Michal Oszmaniec (ICFO), Sanah Altenburg, Sabine Wolkl, Otfried Ghune (University of Siegen) )
We consider a system of N particles distributed on a line whose internal, spin-like, degrees of freedom interact with a space-varying magnetic field. In this way, probing the time evolution of the system allows to estimate the gradient of the magnetic field. Classically, gradient estimation is based on precise measurements of the magnetic field at two different locations, performed with two independent groups of particles. However, this approach is sensitive to fluctuations of the off-set field determining the level-splitting of the ions and therefore suffers from collective dephasing. In our work, we concentrate on states which are insensitive to these fluctuations, and which form therefore a decoherence-free subspace (DFS). At the same time, states from the DFS allow to measure the gradient directly, without the necessity to estimate the value of the offset field. We use the framework of quantum metrology to assess the maximal accuracy of the precision of gradient estimation. We find that states from the DFS achieve the greatest measurement sensitivity (quantified by quantum Fisher information), and find measurements saturating the quantum Cramer-Rao bound. Our results are valid for arbitrary spacing of particles. The measurement accuracy (characterized by the standard deviation) of the optimal state of the DFS are only twice as big as the accuracy of the optimal state of the full Hilbert space without dephasing. We also discuss the concrete implementation of our scheme with trapped ions.

36. Krzysztof Pawłowski
      Centrum Fizyki Teoretycznej PAN (POLAND)
Classical motion saving quantum entanglement: TACT model
(Dariusz Kajtoch, Krzysztof Pawłowski and Emilia Witkowska)
We analyze a scheme for storage of entanglement quantified by the quantum Fisher information in the two-axis countertwisting model (TACT). A characteristic feature of the TACT Hamiltonian is the existence of the four stable center and two unstable saddle fixed points in the mean-field phase portrait. The entangled state is generated dynamically from an initial spin-coherent state located around an unstable saddle fixed point. At an optimal moment of time the state is shifted to a position around the stable center fixed points by a single rotation, where its dynamics and properties are approximately frozen. We also discuss evolution with noise. In some cases the effect of noise turns out to be relatively weak, which is explained by parity conservation.

37. Daniel Pecak
      Institute of Physics of the Polish Academy of Sciences (Poland)
Spatial separation and its transition in a one-dimensional system of a few fermions
(Daniel Pecak, Tomasz Sowinski)
Properties of the ground-state of a two-component mixture of a few fermions with different mass is studied within an exact diagonalization approach. It is shown that depending on a shape of an external confinement different spatial separations between components, manifested by specific shapes of density profiles, can be obtained in the strong interaction limit. We find that the system studied undergoes a particular transition between orderings when the confinement is changed adiabatically from the uniform box to the harmonic oscillator shape. We study properties of this transition in the framework of the finite-size scaling method adopted to a few-body systems. Our findings generalize previous results on the separation induced by the mass difference between components.

38. Marcin Plodzien
      Eindhoven University of Technology (Netherlands)
Rydberg dressing of a one-dimensional BEC
(Marcin Plodzien)
We study the influence of Rydberg dressed interactions in a one-dimensional Bose-Einstein Condensate. We show that 1D is preferential for observing BEC Rydberg dressing. BEC dressing can by studied by investigation of the collective BEC dynamics after a rapid switch-off of the Rydberg-dressing laser. The results can be interpreted as an effective modification of the s-wave scattering length. We include this modification in an analytical model for the BEC, and compare it to full numerical calculations of the Rydberg dressing under realistic experimental conditions.

39. Marek Rams
      Jagiellonian University (Poland)
Enhancing quantum annealing in disordered spin chains
(Marek M. Rams, Adolfo del Campo, Masoud Mohseni)
Techniques to control or assist adiabatic dynamics are of broad interest in quantum technologies, in particular in the context of quantum simulation and adiabatic quantum computation. When the parameters of the Hamiltonian are driven across a second order phase transition at a finite rate then the system gets excited from its ground state leaving the adiabatic manifold. While a variety of protocols have been proposed to reduce this problem in systems without disorder, the development of techniques to approach adiabatic limits in disordered systems is much more limited. In this work we focus on a disordered spin chain. We show that introducing spatially inhomogeneous protocol allows to drive a such a system almost adiabatically across a quantum phase transition, which is practically unattainable with the standard homogeneous protocol. Subsequently we consider generalization of inhomogeneous protocol to achieve scalability with the size of the system.

40. Katarzyna Roszak
      Wrocław University of Technology (Poland)
Qubit-environment entanglement generation during pure dephasing
(K. Roszak, Ł. Cywiński)
We consider the coupling of a qubit in a pure state to an environment in an arbitrary state, and characterize the possibility of qubit-environment entanglement generation during the evolution of the joint system, that leads to pure dephasing of the qubit. We give a simple necessary and sufficient condition on the initial density matrix of the environment together with the properties of the interaction, for appearance of qubit-environment entanglement. Any entanglement created turns out to be detectable by the Peres-Horodecki criterion [1,2]. Furthermore, we show that for a large family of initial environmental states, the appearance of nonzero entanglement with the environment is necessarily accompanied by a change in the state of the environment (i.e. by the back-action of the qubit) [3]. [1] A. Peres, Phys. Rev. Lett. 77, 1413–1415 (1996). [2] M. Horodecki, P. Horodecki, and R. Horodecki, Phys. Lett. A 223, 1–8 (1996). [3] K. Roszak and Ł. Cywiński, Phys. Rev. A 92, 032310 (2015).

41. Julius Ruseckas
      Institute of Theoretical Physics and Astronomy, Vilnius University (Lithaunia)
Engineering of correlated photon pairs via interaction between Rydberg atoms during the storage of slow light
(J. Ruseckas, I. A. Yu, and G. Juzeliunas)
Atoms excited to high-lying Rydberg states with a principal quantum number n above 50 have recently attracted a significant attention [1]. The strong interaction between the Rydberg atoms has been used in quantum information processing[2], studies of interacting many-body systems[3], as well as non-linear quantum optics for slow light [4,5,6]. Here we propose and analyse a method to create two-photon states in a controllable way using the interaction between Rydberg atoms. The main ingredient of the procedure is storage and retrieval of the slow light into two coherences of an atomic medium under conditions of EIT [7]. Interaction between the atoms during the storage period creates entangled pairs of atoms in a superposition state that is orthogonal to the initially stored state. Restoring the slow light from this new atomic state one can produce a two photon state with the second-order correlation function determined by the atom-atom interactions and the storage time. In addition, measurement of the restored light allows one to probe the atom-atom coupling by optical means, with the sensitivity that can be increased by increasing the storage time. As a realization of this idea we consider a many-body Ramsey-type technique [8,9] which involves π/2 pulses creating a superposition of Rydberg states at the beginning and the end of the storage period. In that case the regenerated correlated photons are created due to the resonance dipole-dipole interaction between the atoms in the Rydberg states. [1] M. Saffman, T. G. Walker, and K. Mølmer, Rev. Mod. Phys. 82, 2313 (2010). [2] E. Urban, T. A. Johnson, T. Henage, L. Isenhower, D. D. Yavuz, T. G. Walker, and M. Saffman, Nat. Phys. 5, 110 (2009). [3] P. Schauss, J. Zeiher, T. Fukuhara, S. Hild, M. Cheneau, T. Macrì, T. Pohl, I. Bloch, and C. Gross, Science 347, 1455 (2015). [4] D. Petrosyan, J. Otterbach, and M. Fleischhauer, Phys. Rev. Lett. 107, 21360 (2011). [5] A. V. Gorshkov, J. Otterbach, M. Fleischhauer, T. Pohl, and M. D. Lukin, Phys. Rev. Lett. 107, 133602 (2011). [6] D. Chang, V. Vuletíc, and M. D. Lukin, Nature Photonics 8, 685 (2014). [7] M.-J. Lee, J. Ruseckas, C.-Y. Lee, V. Kudriašov, K.-F. Chang, H.-W. Cho, G. Juzeliūnas, and I. A. Yu, Nat. 
Commun. 5, 5542 (2014). 
 [8] M. Knap, A. Kantian, T. Giamarchi, I. Bloch, M.  D. 
Lukin, and E. Demler, Phys. Rev. Lett. 111, 147205 
 [9] X. Zhang, M. Bishof, S. L. Bromley, C. V. Kraus, M. S. Safronova, P. Zoller, A. M. Rey, and J. Ye, Science 345, 1467 (2014).

42. Amin Salami Dehkharghani
      Aarhus University (Denmark)
Semi-Analytical Approach to the Impenetrable Particles in One-Dimensional Harmonic Traps and Applications of This Model
(Amin S. Dehkharghani)
We introduce our newly developed semi-analytical approach to the strongly interacting two-component particles in one-dimensional harmonic traps. We go in details on how we use the hard-core properties of the particles in the strongly interacting regime to solve the system analytically. In addition, the use of hyperspherical coordinates and some other transformations will be discussed. We illustrate some results in form of density-plots and energies for different kind of mass-imbalanced particles. At the end, we focus on our another idea of how one can use the information obtained in strongly interacting and non-interacting limit to predict the wave function and its corresponding energy for any system with some finite arbitrary interaction strength. The poster will be based on the two recently submitted articles: http://arxiv.org/abs/1511.01702 http://arxiv.org/abs/1512.08905

43. Laurent Sanchez-Palencia
      CNRS and Univ Paris-Saclay (France)
Mott transition for strongly interacting one-dimensional bosons in a shallow periodic potential
(G. Boéris, L. Gori, M. D. Hoogerland, A. Kumar, E. Lucioni, L. Tanzi, M. Inguscio, T. Giamarchi, C. D’Errico, G. Carleo, G. Modugno, and L. Sanchez-Palencia)
We investigate the superfluid-insulator transition of one-dimensional interacting bosons in both deep and shallow periodic potentials. We compare a theoretical analysis based on quantum Monte Carlo simulations in continuum space and Luttinger liquid approach with experiments on ultracold atoms with tunable interactions and optical lattice depth. Experiments and theory are in excellent agreement. Our study provides a quantitative determination of the critical parameters for the Mott transition and defines the regimes of validity of widely used approximate models, namely, the Bose-Hubbard and sine-Gordon models.

44. Kazuyuki Sekizawa
      Faculty of Physics, Warsaw University of Technology (Poland)
Topological excitations from the perspective of nuclear physicists
(Kazuyuki Sekizawa, Gabriel Wlazłowski, Piotr Magierski)
There are various exciting phenomena in cold atomic gases, related to the dynamics of topological excitations, like vortices and solitons. Surprisingly such phenomena also play an important role in nuclear physics. A prominent example is a phenomenon related to vortices in the neutron star. In nuclear astrophysics, the rotational frequency of a pulsar - a rotating neutron star - is one of the few important observables. Detailed, continuous observations have revealed that the frequency shows a sudden increase, which is called glitch. It has been suggested that the glitch is caused by a catastrophic unpinning of a huge number of vortices of superfluid neutrons from pinning sites, a lattice of nuclei. Obviously, the interaction between a quantum vortex and an obstacle (nucleus) is the key ingredient to understand the glitch. In this talk, I will present recent results of our microscopic simulations based on the time-dependent density functional theory (TDDFT) for the vortex-nucleus interaction. Very recently, using the same theoretical framework, we have found observable effects in collisions of two nuclei with different phases of the order parameter. The effects show strong dependence on the relative phase, which may be attributed to the creation of solitonic excitations - phenomenon which is well known in the field of ultracold atomic gases. I will discuss the observed effects emphasizing differences and similarities between nuclear and atomic systems.

45. Piotr Sierant
      Instytut Fizyki imienia Mariana Smoluchowskiego, Uniwersytet Jagielloński (Poland)
Many-body localization due to random interactions
(Piotr Sierant, Dominique Delande, Jakub Zakrzewski)
Many-body localized (MBL) systems, i.e. systems that do not thermally equilibrate under their own dynamics but rather evolve in such a way that the memory about local features of the initial state is preserved, have recently received a lot of attention. We consider a system of ultracold atoms in one-dimensional optical lattice with disordered on-site interparticle interactions. The MBL is found to occur in the system for sufficient density of atoms as one increases the interactions. The single-particle extended states are eigenstates in the absence of the disorder. Therefore, the observed localization is an inherent effect of the interactions and thus a genuine many-body effect. The localization is inspected by means of eigenvalue statistics as well as by time propagation of appropriately prepared initial states.

46. Giacomo Spagnolli
      LENS - European Laboratory for Non-Linear Spectroscopy (Italia)
Parity symmetry breaking and hysteresis with BECs with tunable interactions in a double-well potential
( Andreas Trenkwalder, Giacomo Spagnolli, Giulia Semeghini, Simon Coop, Manuele Landini, Patricia Castilho, Luca Pezzè, Giovanni Modugno, Massimo Inguscio, Augusto Smerzi, Marco Fattori)
In this work we report the experimental observation of the full phase diagram across a transition where the spatial parity symmetry is broken [1]. Our system consists of an ultra-cold gas of 39 K with tunable interactions trapped in a double-well potential. At a critical value of the interaction strength, we observe a continuous quantum phase transition where the gas localizes in one well or the other, thus breaking the underlying symmetry of the system. Furthermore, we show the robustness of the asymmetric state against controlled energy mismatch between the two wells. This is the result of hysteresis associated with an additional discontinuous quantum phase transition that we fully characterize. Our results pave the way to the study of quantum critical phenomena at finite temperature, the investigation of macroscopic quantum tunneling of the order parameter in the hysteretic regime and the production of quantum entangled states at critical points including Schroedinger cat states with macroscopic atom number. [1] A. Trenkwalder, G. Spagnolli, G. Semeghini, S. Coop, M. Landini, P. Castilho, L. Pezzè, G. Modugno, M. Inguscio, A. Smerzi, M. Fattori, Nature Physics (2016) doi:10.1038/nphys3743

47. Julia Stasinska
      Institute of Physics of PAS (Poland)
1D Bose-Hubbard model with extended correlated hopping
(Julia Stasińska et al.)
Ultracold bosonic atoms in one-dimensional, spin-dependent nonoverlapping optical lattices are described by a nonstandard Bose-Hubbard model with next-nearest-neighbour correlated hopping. We study the phase diagram of such system in particular how the extended correlated hopping term affects the Mott transition.

48. Dominik Suszalski
      Instytut Fizyki UJ (Polska)
Emergent lattices with non-separable real and synthetic dimensions
(D. Suszalski)
Ultracold atoms in optical lattices may serve as quantum simulators due to an unprecedented possibility of controlling the system parameters. Recently, the proposition was made to extend the geometry of optical lattice by an additional synthetic dimension using spin degrees of freedom. In my speech I will present the extension of the known emerging geometries by examples when the synthetic dimension cannot be separated from spatial degrees of freedom. The proposed experimental realisation requires the presence of an additional linear potential and uses Raman prosesses to generate new well controllable tunnelings.

49. Tomasz Swislocki
      Warsaw University of Life Sciences - SGGW (Poland)
Non-adiabatic quantum phase transition in a trapped spinor condensate
(Tomasz Swislocki, Emilia Witkowska and Michal Matuszewski)
We study the effect of an inhomogeneity on an outcome of non-adiabatic quantum phase transition from an antiferromagnetic to a phase-separated state in a spin-1 atomic condensate. Double universality in dynamics has been manifested for uniform system due to conservation of magnetization leading to two scaling laws. The first refers to density of spin domain seeds just after the phase transition and it has been explained by the standard Kibble-Zurek mechanism. The second one describes scaling of spin domains density in final stable configurations induced by the postselection process. Presence of an external trapping potential persists the double universality in the dynamics. However, scaling exponents cannot be simply explained by the local density approximation. In order to clarify scaling laws the additional process of magnetization transfer across the system has to be taken into account.

50. Andrzej Syrwid
      Jagiellonian University in Krakow (Poland)
Dynamics of quantum dark solitons
(Andrzej Syrwid, Mirosław Brewczyk, Mariusz Gajda, Krzysztof Sacha)
Eigenstates of Bose particles with repulsive contact interactions in one-dimensional space with periodic boundary conditions can be found with the help of the Bethe ansatz. The type II excitation spectrum identified by E. H. Lieb, reproduces the dispersion relation of dark solitons in the mean-field approach. The corresponding eigenstates possess translational symmetry which can be broken in measurements of positions of particles. We analyze emergence of single and double solitons in the course of the measurements and investigate dynamics of the system. In the weak interaction limit, the system follows the mean-field prediction for a short period of time. Long time evolution reveals many-body effects that are related to an increasing uncertainty of soliton positions. In the strong interaction regime particles behave like impenetrable bosons. Then, the probability densities in the configuration space become identical to the probabilities of non-interacting fermions but the wave-functions themselves remember the original Bose statistics. Especially, the phase flips that are key signatures of the solitons in the weak interaction limit, are preserved in the time evolution of the strongly interacting bosons.

51. Piotr Szankowski
      Institute of Physics, Polish Academy of Sciences (Poland)
Spectroscopy of cross-correlations of environmental noises with two qubits
(P. Szankowski, M. Trippenbach, L. Cywinski)
A single qubit driven by an appropriate sequence of control pulses can serve as a spectrometer of local noise affecting its energy splitting. We show that by driving and observing two spatially separated qubits, one can reconstruct the spectrum of cross-correlations of noises acting at various locations. When the qubits are driven by the same sequence of pulses, real part of cross-correlation spectrum can be reconstructed, while applying two distinct sequence to the two qubits allows for reconstruction of imaginary part of this spectrum. The latter quantity contains information on either causal correlations between environmental dynamics at distinct locations, or on the occurrence of propagation of noisy signals through the environment. We illustrate the former case by modeling the noise spectroscopy protocol for qubits coupled to correlated two-level systems. While entanglement between the qubits is not necessary, its presence enhances the signal from which the spectroscopic information is reconstructed. This work is supported by funds of Polish National Science Center (NCN) under decision no. DEC-2012/07/B/ST3/03616. [arXiv:1507.03897]

52. Gergely Szirmai
      Wigner Research Centre for Physics (Hungary)
Quanatum Magnetism with four component fermions
(D. Jakab, E. Szirmai, M. Lewenstein, and G. Szirmai)
We investigate magnetic properties of strongly interacting four component spin-3/2 ultracold fermionic atoms in the Mott insulator limit with one particle per site in an optical lattice. In this limit, atomic tunneling is virtual, and only the atomic spins can exchange. We find a competition between symmetry-breaking and liquidlike disordered phases. Particularly interesting are valence bond states with bond centered magnetizations, situated between the ferromagnetic and conventional valence bond phases. In the framework of a mean-field theory, we calculate the phase diagram and identify an experimentally relevant parameter region where a homogeneous SU(4) symmetric Affleck-Kennedy-Lieb-Tasaki–like valence bond state is present.

53. Konrad Szymański
      Uniwersytet Jagielloński (Polska)
Evolution of entanglement in the presence of losses
(Konrad Szymański, Krzysztof Pawłowski)
A system with Ising–like Hamiltonian and one–body losses modelling two bipartite Bose–Einstein condensates has been analyzed for the emergence of entanglement. A study of entanglement entropy and parameters describing nonlocality of correlations has been performed. The results have been compared to these known for the lossless case: they are indicating that effect of losses in interesting time span are relatively small and allow for measurement of EPR entanglement.

54. Jordi Tura Brugués
      ICFO - The Institute of Photonic Sciences (Spain)
Nonlocality in fermionic systems and new optimal Bell inequalities
(J. Tura, G. de las Cuevas, R. Augusiak, M. Lewenstein, A. Acín and J. I. Cirac)
We present a method to show that the ground states of some quadratic Hamiltonians in fermionic operators are nonlocal. The same method can be used from the opposite point of view; namely, as a new method to optimize certain Bell inequalities. The method consists of finding the ground state energy of the Hamiltonian by exact diagonalization, which corresponds to the quantum value of a Bell inequality assigned in a natural way. We also find the classical bound of the Bell inequality using dynamic programming. In the translationally invariant (TI) case, we provide analytically closed expressions of the quantum value and an exponentially faster solution of the classical bound. We apply our method to three examples: a tight TI inequality for 8 parties, a quasi TI uniparametric inequality for any even number of parties and we show that the ground state of a spin glass is nonlocal in some parameter region. This paves the way for the use of ground states of commonly studied Hamiltonians as multipartite resources for quantum information protocols that require nonlocality.

55. Tomasz Wasak
      Faculty of Physics, University of Warsaw (Poland)
Generation of non-classical states of light due to single atom interaction in optical cavity for quantum enhanced metrology
(K. Gietka, T. Wasak, F. Piazza, J. Chwedenczuk, H. Ritsch)
Non-classical states of light are an important resource for many quantum technologies. Among these is the quantum-enhanced metrology promising precision of measurement which is beyond the classical limits. We propose an interferometric setup consisting of a single atom interacting with the field of light in an optical cavity. As a result of this interaction, the atom, together with the light, form a composite entangled quantum system. We show, that the detection of a state of the atom passing through the cavity renders the state of light to be highly non-classical. This, as we argue allows for interferometric sensitvity below the shot noise limit.

56. Emilia Witkowska
      Institute of Physics, Polish Academy of Science (Poland)
Spin squeezing in dipolar spinor condensates
(D. Kajtoch, E. Witkowska)
We present our recent work [1] concerning an effect of dipolar interactions on the level of squeezing in spin-1 Bose-Einstein condensates. The system Hamiltonian is conveniently written in terms of the spin and nematic-tensor operators that constitute the SU(3) Lie algebra under the single mode approximation. We limit our consideration to the SU(2) Lie subalgebra spanned by spin operators. The biaxial nature of dipolar interactions allows for dynamical generation of spin-squeezed states in the system. We will show phase portraits in the reduced mean-field phase space in order to determine positions of unstable fixed points which set convenient initial locations of spin coherent states. We will present numerical results for the spin squeezing parameter showing that it is possible to reach the strongest squeezing set by the two-axis countertwisting model. We will explain scaling with the system size by using Gaussian approach and the frozen spin approximation. [1] D. Kajtoch and E. Witkowska, Phys. Rev. A, 93, 023627 (2016).

57. Gabriel Wlazlowski
      Warsaw University of Technology, Faculty of Physics (Poland)
Temperature evolution of transport coefficients in ultracold fermionic gases
(Gabriel Wlazlowski)
In my talk I will present results for various transport coefficients (viscosities, spin responses) extracted for ultracold fermionic gases. The coefficients are extracted by means of ab initio approach based on finite temperature quantum Monte Carlo calculations and the Kubo linear-response formalism. The temperature evolution of these coefficients will be discussed. Typically the transport coefficients show a smooth and monotonic behavior with temperature when crossing the critical temperature T_c, until the Fermi liquid regime is attained at the temperature T*, where the pseudogap regime disappears. I will also show that the clouds of dilute Fermi gas near unitarity exhibit the unusual attribute: for the sizes realized so far in the laboratory or larger (less than 10^9 atoms), it can sustain quantum turbulence below the critical temperature, but at the same time the classical turbulence is suppressed in the normal phase.