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Andrey R. Kolovsky

Publications and source records attributed to Andrey R. Kolovsky.

53 records · Page 3Linked to original sources
arXiv2011

Hall conductivity beyond the linear response regime

The paper introduces a semi-analytical method for calculating the Hall conductivity in the single-band approximations. The method goes beyond the linear response theory and, thus, imposes no limitation on the electric fields magnitude. It is shown that the Hall current decreases with increase of the electric field, if the Bloch frequency (which is proportional to the electric field) exceeds the cyclotron frequency (which is proportional to the magnetic field). The obtained results can be directly applied to the system of cold Bose atoms in a 2D optical lattice, where the single-band approximation is well justified.

cond-mat.mes-hall↗
arXiv2010

Dynamics of interacting atoms in driven tilted optical lattices

The dynamics of cold Bose atoms in driven tilted optical lattices is analyzed focusing on destruction of Wannier-Stark localization and the phenomenon of band collapse. It is argued that an understanding of the experimental results requires thorough account for interaction effects. These are suppression of the ballistic spreading of atoms for resonant driving (a multiple of the driving frequency coincides with the Bloch frequency) and unbounded sub-diffusive spreading of atoms for off-resonant driving.

quant-ph↗
arXiv2010

Bright solitons and self-trapping with a BEC of cold atoms in driven tilted optical lattices

We suggest a method for creating bright matter solitons by loading a BEC of atoms in a driven tilted optical lattice. It is shown that one can realize the self-focussing regime for the wave-packet dynamics by properly adjusting the phase of the driving field with respect to the phase of Bloch oscillations. If atom-atom interactions are larger than some critical value $g_{min}$, this self-focussing regime is followed by the formation of bright solitons. Increasing the interactions above another critical value $g_{max}$ makes this process unstable. Instead of soliton formation one now meets the phenomenon of incoherent self-trapping. In this regime a fraction of atoms is trapped in incoherent localized wave-packets, while the remaining atoms spread ballistically.

cond-mat.quant-gas↗
arXiv2009

Bloch oscillations of Bose-Einstein condensates: Quantum counterpart of dynamical instability

We study the Bloch dynamics of a quasi one-dimensional Bose-Einstein condensate of cold atoms in a tilted optical lattice modeled by a Hamiltonian of Bose-Hubbard type: The corresponding mean-field system described by a discrete nonlinear Schrödinger equation can show a dynamical (or modulation) instability due to chaotic dynamics and equipartition over the quasimomentum modes. It is shown, that these phenomena are related to a depletion of the Floquet-Bogoliubov states and a decoherence of the condensate in the many-particle description. Three different types of dynamics are distinguished: (i) decaying oscillations in the region of dynamical instability, and (ii) persisting Bloch oscillations or (iii) periodic decay and revivals in the region of stability.

quant-ph↗
arXiv2009

Bose-Einstein condensates on tilted lattices: coherent, chaotic and subdiffusive dynamics

The dynamics of a (quasi)one-dimensional interacting atomic Bose-Einstein condensate in a tilted optical lattice is studied in a discrete mean-field approximation, i.e., in terms of the discrete nonlinear Schrödinger equation. If the static field is varied the system shows a plethora of dynamical phenomena. In the strong field limit we demonstrate the existence of (almost) non-spreading states which remain localized on the lattice region populated initially and show coherent Bloch oscillations with fractional revivals in the momentum space (so called quantum carpets). With decreasing field, the dynamics becomes irregular, however, still confined in configuration space. For even weaker fields we find sub-diffusive dynamics with a wave-packet width spreading as $t^{1/4}$.

quant-ph↗
arXiv2008

Atomic current in optical lattices: Esaki-Tsu equation revisited

The paper discusses the master equation approach to derivation of the Esaki-Tsu equation for drift current. It is shown that the relaxation term in the master equation can be identified by measuring the velocity distribution of the carriers. We also show that the standard form of the relaxation term, used earlier to derive Esaki-Tsu equation, predicts unphysical velocity distribution and suggest a more elaborated relaxation term, which is argued to correctly capture the effect of bosonic bath in experiments on atomic current in optical lattices.

quant-ph↗
arXiv2007

Semiclassical quantization of the Bogoliubov spectrum

We analyze the Bogoliubov spectrum of the 3-sites Bose-Hubbard model with finite number of Bose particles by using a semiclassical approach. The Bogoliubov spectrum is shown to be associated with the low-energy regular component of the classical Hubbard model. We identify the full set of the integrals of motions of this regular component and, quantizing them, obtain the energy levels of the quantum system. The critical values of the energy, above which the regular Bogoliubov spectrum evolves into a chaotic spectrum, is indicated as well.

cond-mat.stat-mech↗
arXiv2006

Persistent current of atoms in a ring optical lattice

We consider a small ensemble of Bose atoms in a ring optical lattice with weak disorder. The atoms are assumed to be initially prepared in a superfluid state with non-zero quasimomentum and, hence, may carry matter current. It is found that the atomic current persists in time for a low value of the quasimomentum but decays exponentially for a high (around one quater of the Brillouin zone) quasimomentum. The explanation is given in terms of low- and high-energy spectra of the Bose-Hubbard model, which we describe using the Bogoliubov and random matrix theories, respectively.

cond-mat.soft↗
arXiv2006

Emergence of superfluid transport in a dynamical system of ultracold atoms

The dynamics of a Bose-Einstein condensate is studied theoretically in a combined periodic plus harmonic external potential. Different dynamical regimes of stable and unstable collective dipole and Bloch oscillations are analysed in terms of a quantum mechanical pendulum model. Nonlinear interactions are shown to counteract quantum-mechanical dephasing and lead to phase-coherent, superfluid transport.

cond-mat.other↗
arXiv2006

Bloch oscillations of strongly interacting Bose atoms

We analyse Bloch oscillations (i.e., oscillations induced by a static force) of strongly interacting Bose atoms {\em beyond} the hard-core bosons model. It is shown that residual interactions between the atoms modulate Bloch oscillations, where the type of modulations depends on the magnitude of the static force.

cond-mat.other↗
arXiv2005

Atomic current across an optical lattice

We devise a microscopic model for the emergence of a collision-induced, fermionic atomic current across a tilted optical lattice. Tuning the - experimentally controllable - parameters of the microscopic dynamics allows to switch from Ohmic to negative differential conductance.

cond-mat.other↗
arXiv2004

Dynamical instability, Chaos, and Bloch oscillations of Bose-Einstein condensates in tilted optical lattices

We study the Bloch dynamics of a Bose-Einstein condensate of cold atoms by using the formalism of the discrete nonlinear Schroedinger equation. Depending on the static force magnitudes the system is shown to exhibit two qualitatively different regimes of Bloch oscillations - exponential decay for the static force magnitude less than some critical value (defined by the condensate density) and quasiperiodic oscillations in the opposite case. The relation of these regimes to the onset of chaos in the system is discussed.

cond-mat.other↗
arXiv2004

Bloch oscillations of cold atoms in optical lattices

This work is devoted to Bloch oscillations (BO) of cold neutral atoms in optical lattices. After a general introduction to the phenomenon of BO and its realization in optical lattices, we study different extentions of this problem, which account for recent developments in this field. These are two-dimensional BO, decoherence of BO, and BO in correlated systems. Although these problems are discussed in relation to the system of cold atoms in optical lattices, many of the results are of general validity and can be well applied to other systems showing the phenomenon of BO.

cond-mat.soft↗
arXiv2004

Quantum Chaos in the Bose-Hubbard model

We present a numerical study of the spectral properties of the 1D Bose-Hubbard model. Unlike the 1D Hubbard model for fermions, this system is found to be non-integrable, and exhibits Wigner-Dyson spectral statistics under suitable conditions.

cond-mat.soft↗
arXiv2003

Multi-particle quantum chaos in tilted optical lattices

We show that, in the parameter regime of state of the art experiments on Bose Einstein Condensates loaded into optical lattices, the energy spectrum of the 1D Bose-Hubbard model amended by a static field exhibits unambiguous signatures of quantum chaos. In the dynamics, this leads to the irreversible decay of Bloch oscillations.

cond-mat.soft↗
arXiv2003

"Bloch oscillations" in the Mott-insulator regime

We study the dynamical response of cold interacting atoms in the Mott insulator phase to a static force. As shown in the experiment by M. Greiner et. al., Nature \textbf{415}, 39 (2002), this response has resonant character, with the main resonance defined by coincidence of Stark energy and on-site interaction energy. We analyse the dynamics of the atomic momentum distribution, which is the quantity measured in the experiment, for near resonant forcing. The momentum distribution is shown to develop a recurring interference pattern, with a recurrence time which we define in the paper.

cond-mat.soft↗