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1
Content available remote Counterpropagating Matter Waves in Optical Lattices
100%
Prvanović S. , Jović D. , Jovanović R. , Strinić A. , Belić M.
Acta Physica Polonica A
|
2009
|
tom 116
|
nr 4
507-509
EN
An investigation of Bose-Einstein condensate in two-dimensional optical lattice potentials, formed by laser beams, is carried out. We are interested in the dynamics of Bose-Einstein condensate in a square optical lattice, where the periodic potential can lead to the stabilization of an otherwise unstable Bose-Einstein condensate. The behavior of Bose-Einstein condensate in optical lattices is described by the nonlinear Gross-Pitaevskii equation, which we treat numerically. By applying the Petviashvili iteration method, we demonstrate the existence of solitonic solutions in the case of counterpropagating matter waves, and analyze their stability.
2
Content available remote Electromagnetically Induced Transparency in a Double Well Atomic Josephson Junction
63%
Weatherall J. , Search C.
Acta Physica Polonica A
|
2009
|
tom 116
|
nr 4
455-459
EN
Electromagnetically induced transparency is an important tool for controlling light propagation and nonlinear wave mixing in atomic gases with potential applications ranging from quantum computing to table top tests of general relativity. Here we consider electromagnetically induced transparency in an atomic Bose-Einstein condensate trapped in a double well potential. One well is prepared as in standard electromagnetically induced transparency with a weak probe laser and control laser in a Λp configuration while tunneling between the wells provides a coherent coupling between identical electronic states in the two wells leading to the formation of spatially delocalized inter-well dressed states. The macroscopic inter-well coherence of the Bose-Einstein condensate wave function qualitatively modifies the normal electromagnetically induced transparency linear susceptibility and leads to the formation of additional absorption resonances and larger dispersion than electromagnetically induced transparency. We show that these new resonances can be interpreted in terms of the inter-well dressed states and the formation of a novel type of dark state involving the control laser and the inter-well tunneling.
3
Content available remote Modulation Instability of Two-Dimensional Dipolar Bose-Einstein Condensate in a Deep Optical Lattice
63%
Wöllert A. , Gligorić G. , Škorić M. , Maluckov A. , Raičević N. , Daničić A. , Hadžievski L.
Acta Physica Polonica A
|
2009
|
tom 116
|
nr 4
519-521
EN
We study the stability of the continuous waves in the pancake shaped dipolar Bose-Einstein condensate trapped in the strong optical lattice potential with the coexisting local (the short-range s-wave) interaction and nonlocal (the dipole-dipole) interactions between the condensate atoms. The system is modeled by two two-dimensional discrete models derived from the Gross-Pitaevskii equation accounting the dipole-dipole interactions: discrete nonlinear Schrödinger equation with cubic nonlinearity and nonpolynomial Schrödinger equation. The corresponding dispersion relations are calculated analytically and the regions of the modulation instability in the parametric space are summarized into the stability diagrams.
4
Content available remote Self-Maintaining Defect/Energetic Droplets from Two Interacting Bose-Einstein Condensates
63%
Dzhunushaliev V.
Acta Physica Polonica A
|
2013
|
tom 124
|
nr 4
629-635
EN
We consider two interacting Bose-Einstein condensates with different kinds of the potential energy of interaction of the condensates: (a) the standard potential, (b) the potential has a positive three-body and a negative two-body scattering terms, and (c) the potential has a positive four-body and a negative three-body scattering terms for the first Bose-Einstein condensate and a positive three-body and a negative two-body scattering terms for the second Bose-Einstein condensate. It is shown that in these cases there exist stationary regular spherically symmetric solutions. Physically such solution is either a defect or an energetic droplet created by the condensates. The defect is a cavity filled with one Bose-Einstein condensate on the background of another Bose-Einstein condensate. The droplet is an object with zero energy density at the infinity. For (a) and (b) cases the obtained objects are supported by a constant external trapping potential and for (c) case the droplet is a self-maintaining object without any external potential. The possibility of construction of an elementary logic qubit device on the basis of this droplet is discussed.
5
Content available remote Bose-Hubbard Model in the Rotating Frame of Reference
51%
Polak T. , Kopeć T.
Acta Physica Polonica A
|
2010
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tom 118
|
nr 2
279-282
EN
Following a novel experimental arrangement which can rotate a two-dimensional optical lattice at frequencies up to several kilohertz we discuss the ground state of the two-dimensional Bose-Hubbard Hamiltonian, relevant for rotating gaseous Bose-Einstein condensates, by employing U(1) quantum rotor approach and the topologically constrained path integral. Ultracold atoms in such a rotating lattice can be used for the direct quantum simulation of strongly correlated systems under large effective magnetic fields. We derive an effective quantum action for the Bose-Hubbard model, which enables a non-perturbative treatment of the zero-temperature phase transition in the rotating frame. We calculate the ground-state phase diagram, analytically deriving maximum repulsive energy for several rational values of the frustration rotation parameter f = 0, 1/2, 1/3, 1/4, and 1/6 for the square and triangular lattice. Performed calculations revealed strong non-monotonical dependence of the critical ratio of the kinetic energy to the repulsive on-site energy, that separates the global coherent from the insulating state, on topology of the lattice.
6
Content available remote Neutral Bosonic Condensates in Layered 2D Structures under Artificial Magnetic Field
51%
Polak T. , Zaleski T.
|
EN
We show that the properties of the ideal Bose gas in three-dimensional optical lattice can be closely mimicked by finite two dimensional systems with only ten of layers. The match between critical properties strongly depends on the anisotropy of the hopping amplitudes in and between layers which we fully control. The theory we provided can be directly used in the experiments and results in less challenging requirements of the setups. We also present the phase diagram with its non-monotonic dependence of the ratio of tunneling to on-site repulsion when artificial magnetic field is applied to the system.
7
Content available remote Conductivity of Strongly Correlated Bosons in the Simple Cubic Lattice - Magnetic Field and Hopping Anisotropy Effects
51%
Sajna A. , Polak T. , Micnas R.
Acta Physica Polonica A
|
2015
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tom 127
|
nr 2
448-450
EN
We investigate optical conductivity in three dimensional system of bosons under strong magnetic field. In particular, we consider Bose Hubbard model in the strongly correlated limit, where Mott insulator phase emerges. For chosen rational number of magnetic flux per cell we show that response of the system gains complex peaks behavior on the order of frequency corresponding to on-site boson repulsive interaction. Moreover, when anisotropy in hopping energy for the direction parallel to magnetic field is tuned up, the non-monotonous behavior of the optical conductivity could appear. The obtained results can be experimentally probed in the system of ultracold atoms loaded on an optical lattice.
8
Content available remote Quantum Rotor Approach to the Mott-Insulator Transition in the Bose-Hubbard Model
51%
Polak T. , Kopeć T.
Acta Physica Polonica A
|
2008
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tom 114
|
nr 1
29-34
EN
We present the novel approach to the Bose-Hubbard model using the U(1) quantum rotor description. We formulate a problem in the phase only action using an effective action formalism and obtain analytical formulae for the critical lines. We show that the nontrivial U(1) phase field configurations have an impact on the phase diagrams. The topological character of the quantum field is governed by terms of the integer charges -- winding numbers n. The comparison of the presented results with recently obtained quantum Monte Carlo numerical calculations suggests that the competition between quantum effects in strongly interacting boson systems is correctly captured by our model.
9
Content available remote Extracting Information from Non Adiabatic Dynamics: Excited Symmetric States of the Bose-Hubbard Model
51%
Łącki M. , Delande D. , Zakrzewski J.
Acta Physica Polonica A
|
2011
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tom 120
|
nr 6A
A-178-A-184
EN
Using Fourier transform on a time series generated by unitary evolution, we extract many-body eigenstates of the Bose-Hubbard model corresponding to low energy excitations, which are generated when the insulator-superfluid phase transition is realised in a typical experiment. The analysis is conducted in a symmetric external potential both without and with a disorder. A simple classification of excitations in the absence disorder is provided. The evolution is performed assuming the presence of the parity symmetry in the system rendering many-body quantum states either symmetric or antisymmetric. Using symmetry-breaking technique, those states are decomposed into elementary one-particle processes.
10
Content available remote Lost of Bosonic Coherence Due to the Fermionic Presence Under the Synthetic Magnetic Field
51%
Polak T.
|
|
nr 4
759-763
EN
We have studied effects of inter-species interaction of the bosons in a Bose-Fermi mixture over a large regime of particle numbers under the synthetic magnetic field. Analytically derived formulas for the density of states for several values of the magnetic fields f=1/2,1/3,1/4,1/6,1/8 and 3/8 allows us to calculate, with a very good accuracy, the effective interaction between bosons. The presence of the Hofstadter butterfly spectrum and fermionic species induces alternating sign potential between neutral bosonic atoms. Consequently bosons can attract or repulse each other whether sign of it strongly depends on the strength of the magnetic field applied to the sample.
11
Content available remote Effect of Structural Potential on Magnetic Vortex Solitons in Spatially 1D-Extended Josephson Junction
51%
Al-Khawaja S.
Acta Physica Polonica A
|
2013
|
tom 124
|
nr 1
35-40
EN
Soliton evolution in spatially extended Josephson junction is studied for three types of ad hoc structural potentials describing tunnelling magnetic flux vortices; symmetric, ratchet and double-well. Setting from the inline geometry of the junction, the soliton dynamics could be modelled by the perturbed sine-Gordon equation. Numerical solutions of the latter equation yielded the soliton waves of the fluxon phase, for boundary conditions imposed on the system upon variation of the dispersion parameter α. It has been found that a change in the soliton waveform and intensity occurs as α goes higher, in dependence on the functional of the potential and its symmetry properties. For ratchet and double-well potential at α=0.5, a time-dependent forcing has been found to endorse the balance between dispersion and nonlinearity, jointly with enhancing the stability of the soliton wave. The McLoughlin-Scott perturbation theory has been adopted to show that the system conserves energy due to the delicate balance between nonlinearity and dispersion, so that the soliton keeps robust as it temporally evolves.
12
Content available remote Phase Transitions in Optical Lattices at Finite Temperatures
51%
Polak T. , Kopeć T.
Acta Physica Polonica A
|
2009
|
tom 115
|
nr 1
418-420
EN
We discuss the finite-temperature phase diagram in three-dimensional Bose-Hubbard model relevant for the Bose-Einstein condensates in optical lattices, by employing U(1) quantum rotor approach and the topologically constrained path integral, that includes a summation over U(1) topological charge. The effective action formalism allows us to formulate a problem in the phase only action and obtain analytical formulae for the critical lines beyond mean-field theory.
13
Content available remote Quantum Bright Soliton in a Disorder Potential
51%
Sacha K. , Delande D. , Zakrzewski J.
Acta Physica Polonica A
|
2009
|
tom 116
|
nr 5
772-778
EN
At very low temperature, a quasi-one-dimensional ensemble of atoms with attractive interactions tend to form a bright soliton. When exposed to a sufficiently weak external potential, the shape of the soliton is not modified, but its external motion is affected. We develop in detail the Bogoliubov approach for the problem, treating, in a non-perturbative way, the motion of the center of mass of the soliton. Quantization of this motion allows us to discuss its long time properties. In particular, in the presence of a disordered potential, the quantum motion of the center of mass of a bright soliton may exhibit Anderson localization, on a localization length which may be much larger than the soliton size and could be observed experimentally.
14
Content available remote On Bright and Dark Breathers in Lattices with Saturable Nonlinearity
51%
Maluckov A. , Stepić M. , Hadžievski L.
Acta Physica Polonica A
|
2007
|
tom 112
|
nr 5
903-908
EN
The moving bright and dark localized modes in one-dimensional optical lattices with saturable nonlinearity are considered with respect to the grand canonical free energy concept and linear stability analysis of the eigenvalue spectra.
15
Content available remote Role of Bandwidths and Energy Gap in Formation of Ground State of Ultra-Cold Bosons in Artificial Magnetic Fields
51%
Patucha K. , Grygiel B. , Zaleski T.
Acta Physica Polonica A
|
2016
|
tom 130
|
nr 2
637-640
EN
We study the properties of ultra-cold bosons in optical lattice in arbitrary gauge potentials. Using quantum rotor approach we are able to go beyond mean-field approximation thus taking into account subtleties of the band structure of the artificial magnetic field. This allows us to elucidate the interplay of the subbands widths and energy gaps on the formation of the coherent state. As a result, we are able to pinpoint the elements of the band structure, which are crucial to proper theoretical description of the synthetic magnetic field in a lattice bosonic system. This leads us finally to a method of approximation of the Hofstadter butterfly spectrum with a simpler band structure and use it to investigate the ground state of the system for a wide range of magnetic fluxes.
16
Content available remote Optical Conductivity of Ultra-Cold Bosons in Optical Lattices
51%
Grygiel B. , Patucha K. , Zaleski T.
Acta Physica Polonica A
|
2016
|
tom 130
|
nr 2
633-636
EN
We study ultra-cold bosonic systems in optical lattice using quantum rotor approach to calculate the current-current correlations, which provides the information about conductivity of the system. The method allows us to go beyond mean-field approximation and track the behavior of the real part of the conductivity along the phase transition between the Mott insulator and superfluid state for various geometries of the lattice. In the phase-ordered state at zero temperature, a discrete ingredient appears resulting from the long-range coherence in the system.
17
Content available remote Spontaneous Currents in a Bosonic Ring
51%
Makieła D. , Maśka M.
Acta Physica Polonica A
|
2016
|
tom 130
|
nr 2
569-572
EN
Nonequilibrium dynamics of non-interacting bosons in a one-dimensional ring-shaped lattice is studied by means of the kinetic Monte Carlo method. The system is approximated by the classical XY model (the kinetic term is neglected) and then the simulations are performed for the planar classical spins. We study the dynamics that follows a finite-time quench to zero temperature. If the quench is slow enough the system can equilibrate and finally reaches the ground state with uniform spin alignment. However, we show that if the quench is faster than the relaxation rate, the system can get locked in a current-carrying metastable state characterized by a nonzero winding number. We analyze how the zero-temperature state depends on the quench rate.
18
Content available remote Dimensional Reduction and Localization of a Bose-Einstein Condensate in a Quasi-1D Bichromatic Optical Lattice
51%
Salasnich L. , Adhikari S.
Acta Physica Polonica A
|
2015
|
tom 128
|
nr 6
979-982
EN
We analyze the localization of a Bose-Einstein condensate in a one-dimensional bichromatic quasi-periodic optical-lattice potential by numerically solving the 1D Gross-Pitaevskii equation (1D GPE). We first derive the 1D Gross-Pitaevskii equation from the dimensional reduction of the 3D quantum field theory of interacting bosons obtaining two coupled differential equations (for axial wave fuction and space-time dependent transverse width) which reduce to the 1D Gross-Pitaevskii equation under strict conditions. Then, by using the 1D Gross-Pitaevskii equation we report the suppression of localization in the interacting Bose-Einstein condensate when the repulsive scattering length between bosonic atoms is sufficiently large.
19
Content available Cold Atomic Gases in Optical Lattices with Disorder
51%
Schulte T. , Drenkelforth S. , Kruse J. , Ertmer W. , Arlt J. , Kantian A. , Sanchez-Palencia L. , Santos L. , Sanpera A. , Sacha K. , Zoller P. , Lewenstein M. , Zakrzewski J.
Acta Physica Polonica A
|
2006
|
tom 109
|
nr 1
89-99
EN
Cold atomic gases placed in optical lattices enable studies of simple condensed matter theory models with parameters that may be tuned relatively easily. When the optical potential is randomized (e.g. using laser speckle to create a random intensity distribution) one may be able to observe Anderson localization of matter waves for non-interacting bosons, the so-called Bose glass in the presence of interactions, as well as the Fermi glass or quantum spin glass for mixtures of fermions and bosons.
20
Content available remote Fermionic Mediated Effective Interaction for the Two-Dimensional Bose-Fermi Mixtures under Artificial Magnetic Field
51%
Polak T.
|
EN
The strongly interacting bosonic and non-interacting fermionic mixtures of diluted gases are studied. An artificial magnetic field is introduced in theory by imposing a Peierls phase shift on the wave functions of the constituents. A highly nontrivial limit of the quantum-Hall limit is achieved which provides oscillations effects of the fermion mediated interaction between bosons. In consequence the effective interaction between bosons can change the magnitude and sign. This provides possible explanations of the bosonic coherence loss observed experimentally in the "time of flight" and "peak width" experiments.
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