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1
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Lost of Bosonic Coherence Due to the Fermionic Presence Under the Synthetic Magnetic Field

100%
Polak T.
Acta Physica Polonica A
|
2012
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vol. 121
|
issue 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.
2
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Fermionic Mediated Effective Interaction for the Two-Dimensional Bose-Fermi Mixtures under Artificial Magnetic Field

100%
Polak T.
Acta Physica Polonica A
|
2012
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vol. 121
|
issue 5-6
1308-1311
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.
3
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Phase Transitions in Optical Lattices at Finite Temperatures

63%
Polak T., Kopeć T.
Acta Physica Polonica A
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2009
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vol. 115
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issue 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.
4
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Self-Induced Resonances in Asymmetric Superconducting Quantum Interference Devices

63%
Polak T., Sarnelli E.
Acta Physica Polonica A
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2008
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vol. 114
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issue 1
203-207
EN
Theory of self-induced resonances in asymmetric two-junction interferometer device is presented. An extension of previous theoretical approaches contains inclusions from several asymmetries: the Josephson current ε, capacitances χand dissipation ρpresented in an equivalent circuit. Our theory can be useful to determine asymmetry parameters always present in lightly damped asymmetric SQUIDs made from low- and high-T_C materials.
5
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Bose-Hubbard Model in the Rotating Frame of Reference

63%
Polak T., Kopeć T.
|
|
issue 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
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Quantum Rotor Approach to the Mott-Insulator Transition in the Bose-Hubbard Model

63%
Polak T., Kopeć T.
Acta Physica Polonica A
|
2008
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vol. 114
|
issue 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.
7
Content available remote

Neutral Bosonic Condensates in Layered 2D Structures under Artificial Magnetic Field

63%
Polak T., Zaleski T.
Acta Physica Polonica A
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2012
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vol. 121
|
issue 5-6
1312-1314
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.
8
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
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2015
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vol. 127
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issue 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.
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