Searcharxiv⌕ Search

arXiv subjects

A. B. Kuklov

Publications and source records attributed to A. B. Kuklov.

32 records · Page 2Linked to original sources
arXiv2002

Groundstates of SU(2)-Symmetric Confined Bose Gas: Trap for a Schrödinger Cat

Conservation of the total isotopic spin S of a two-component Bose gas-like $^{87}$Rb-has a dramatic impact on the structure of the ground state. In the case when S is much smaller than the total number of particles N, the condensation of each of the two components occurs into two single-particle modes. The quantum wavefunction of such a groundstate is a Schrödinger Cat-a superposition of the phase separated classical condensates, the most "probable" state in the superposition corresponding to the classical groundstate in the sector of given N and S. After measurement of the spatial distribution of the densities of the two components, the Cat collapses into one of the classical condensate states.

cond-mat.soft↗
arXiv2001

Symmetries and Decoherence of Two-Component Confined Atomic Clouds: Study of the Atomic Echo in the two-component Bose-Einstein Condensate

Implications of the internal symmetries on the dynamics of the trapped two-component atomic vapors are discussed. In the cases of $^{87}$Rb (bosons) as well as of $^{40}$K (fermions) trapped in the two hyperfine states, the intrinsic $su(2)$ symmetry can be realized with a very good precision. Such a symmetry protects the global operators, which are the generators of the symmetry, from any decoherence. The case of boson-fermion mixture is discussed as well. The role of external factors, breaking the symmetry, in inducing the decoherence of the global operators is considered. It is shown that, the loss of the correlations is not faster than the rates of the induced heating or losses, provided the noise is characterized by short correlation length. The case of the extrinsic long-ranged fluctuations is also considered. Intrinsic mechanisms of decoherence of the correlators of the condensate operators of the two-component condensate are analyzed. The atomic echo is discussed as a test for the reversibility of the phase diffusion effect. The intensity and the profile of the multiple echo are calculated numerically as well as analytically.

cond-mat.soft↗
arXiv2001

Strong interconversion of non-polar phonons and Josephson plasma oscillations induced by equilibrium Josephson currents in high T_c superconductors

We analyze consequences of dynamical modulations of Josephson current by non-polar lattice mode in the Josephson junction barrier. In the high $T_c$ junctions, the effect of such modulations can be anomalously strong due to the proximity of the insulating barrier to the superconducting state. Accordingly, the interconversion of sound (as well as other non-polar phonons) and the Josephson plasma oscillations mediated by stationary Josephson currents, which may be present in the junction due to various reasons, becomes possible. We suggest that this effect can be employed for imaging of the stationary Josephson currents. Estimates of the effect are given.

cond-mat.supr-con↗
arXiv2000

Implications of SU(2) symmetry on the dynamics of population difference in the two-component atomic vapor

We present an exact many body solution for the dynamics of the population difference $N_2-N_1$ induced by an rf-field in the two-component atomic cloud characterized by equal scattering lengths. This situation is very close to the actual JILA experiments with the two-component $^{87}$Rb vapor. We show that no intrinsic decoherence exists for $N_2-N_1$, provided the exact SU(2) symmetry holds. This contrasts with finite dissipation of the normal modes even in the presence of the SU(2) symmetry. The intrinsic decoherence for \$N_2-N_1$ may occur as long as deviations from the exact SU(2) symmetry are taken into account. Such decoherence, however, should be characterized by very long times governed by the smallness of the deviations from the symmetry. We suggest testing the evolution of $N_2-N_1$ by conducting echo-type experiments.

cond-mat.soft↗
arXiv2000

Orthogonality catastrophe and decoherence of a confined Bose-Einstein condensate at finite temperature

We discuss mechanisms of decoherence of a confined Bose-Einstein condensate at finite temperatures under the explicit condition of conservation of the total number of bosons $N$ in the trap. A criterion for the irreversible decay of the condensate two-time correlator is formulated in terms of the {\it Orthogonality Catastrophe} (OC) for the exact N-body eigenstates, so that no irreversible decay occurs without the OC. If an infinite external bath contacts a finite condensate, the OC should practically always occur as long as the bath degrees o freedom are interacting with each other. We claim that, if no external bath is present and the role of the bath is played by the normal component, no irreversible decay occurs. We discuss the role of the effect of the {\it level repulsion} in eliminating the OC. At finite temperatures, the time-correlations of the condensate isolated from the environment are dominated by the reversible dephasing which results from the thermal ensemble averaging over realizations of the normal component. Accordingly, the correlator exhibits the gaussian decay with certain decay time $τ_d$ dependent on temperature as well as on intensity of the shot noise determined by the statistical uncertainty in the number of bosons $N$ deposited into the trap. We estimate $τ_d$ for the conditions resembling those realized in the JILA experiment, and obtain the value close to 1s, if no shot noise is taken into account. At temperatures as large as 0.5 of the temperature of the Bose-Einstein condensation, $τ_d \leq 100$ms. Depending on the variance $ΔN$ of $N$, inclusion of the shot noise may shorten these times.

cond-mat.soft↗
arXiv1999

Testing quantum correlations in a confined atomic cloud by scattering fast atoms: Direct and time reversed processes

We suggest measuring the one-particle density matrix of a trapped ultracold atomic cloud by scattering fast atoms in a pure momentum state off the cloud. The lowest-order probability for the process, resulting in a pair of outcoming fast atoms for each incoming one, as well as of its time reversed counterpart, turns out to be given by the Fourier transform of the density matrix. Accordingly, important information about quantum correlations can be deduced directly from the differential scattering cross-section of these processes. Several most interesting cases of scattering - from a single condensate containing a vortex, and from a split condensate characterized by some phase difference - are discussed.

cond-mat.soft↗
arXiv1999

Detecting Josephson effect in the excitonic condensate by coherent emission of light

Coherent emission of light by a split excitonic Bose-Einstein condensate -- excitonic Josephson junction -- can be extremely sensitive to the Josephson phase established across the junction. As a result of this, the emission can be redistributed between different directions and even cancelled. The cases of the dipole- and of the quadrupole-active excitons are considered.

cond-mat.mes-hall↗
arXiv1998

Testing quantum correlations in a confined atomic cloud by scattering fast atoms

We suggest measuring one-particle density matrix of a trapped ultracold atomic cloud by scattering fast atoms in a pure momentum state off the cloud. The lowest-order probability of the inelastic process, resulting in a pair of outcoming fast atoms for each incoming one, turns out to be given by a Fourier transform of the density matrix. Accordingly, important information about quantum correlations can be deduced directly from the differential scattering cross-section. A possible design of the atomic detector is also discussed.

cond-mat.soft↗
arXiv1998

Landau damping and the echo effect in a confined Bose-Einstein condensate

Low energy collective mode of a confined Bose-Einstein condensate should demonstrate the echo effect in the regime of Landau damping. This echo is a signature of reversible nature of Landau damping. General expression for the echo profile is derived in the limit of small amplitudes of the external pulses. Several universal features of the echo are found. The existence of echo in other cases of reversible damping -- Fano effect and Caldeira-Leggett model -- is emphasized. It is suggested to test reversible nature of the damping in the atomic traps by conducting the echo experiment.

cond-mat.soft↗
arXiv1997

Thermal dephasing and the echo effect in a confined Bose-Einstein condensate

It is shown that thermal fluctuations of the normal component induce dephasing -- reversible damping of the low energy collective modes of a confined Bose-Einstein condensate. The dephasing rate is calculated for the isotropic oscillator trap, where Landau damping is expected to be suppressed. This rate is characterized by a steep temperature dependence, and it is weakly amplitude dependent. In the limit of large numbers of bosons forming the condensate, the rate approaches zero. However, for the numbers employed by the JILA group, the calculated value of the rate is close to the experimental one. We suggest that a reversible nature of the damping caused by the thermal dephasing in the isotropic trap can be tested by the echo effect. A reversible nature of Landau damping is also discussed, and a possibility of observing the echo effect in an anisotropic trap is considered as well. The parameters of the echo are calculated in the weak echo limit for the isotropic trap. Results of the numerical simulations of the echo are also presented.

cond-mat.soft↗
arXiv1996

Quantum Versus Mean Field Behavior of Normal Modes of a Bose-Einstein Condensate in a Magnetic Trap

Quantum evolution of a collective mode of a Bose-Einstein condensate containing a finite number N of particles shows the phenomena of collapses and revivals. The characteristic collapse time depends on the scattering length, the initial amplitude of the mode and N. The corresponding time values have been derived analytically under certain approximation and numerically for the parabolic atomic trap. The revival of the mode at time of several seconds, as a direct evidence of the effect, can occur, if the normal component is significantly suppressed. We also discuss alternative means to verify the proposed mechanism.

cond-mat↗
arXiv1996

Centrifugal Effects in a Bose-Einstein Condensate

Single particle states in the atomic trap employing the rotating magnetic field are found using the full time-dependent instantaneous trapping potential. These states are compared with those of the effective time-averaged potential. We show that the trapping is possible when the frequency of the rotations exceeds some threshold. Slightly above this threshold the weakly interacting gas of the trapped atoms acquires the properties of a quasi-1D system in the frame rotating together with the field. The role of the atom-atom interaction in changing the ideal gas solution is discussed. We show that in the limit of large numbers of particles the rotating field whose angular frequency is appropriately modulated can be utilized as a driving force principally for the center of mass motion as well as for the angular momentum $L = 2$ normal modes of the Bose condensate. A mechanism of quantum evaporation forced by the rotating field is analyzed.

atom-ph↗
arXiv1995

INTERLAYER VORTICES AND EDGE DISLOCATIONS IN HIGH TEMPERATURE SUPERCONDUCTORS

The interaction of an edge dislocation made of half the superconducting plane with a magnetic interlayer vortex is considered within the framework of the Lawrence-Doniach model with negative as well as positive Josephson interlayer coupling. In the first case the binding energy of the vortex and the dislocation has been calculated by employing a variational procedure. The current distribution around the bound vortex turns out to be asymmetric. In the second case the dislocation carries a spontaneous magnetic half-vortex, whose binding energy with the dislocation turns out to be infinite. The half-vortex energy has been calculated by the same variational procedure. Implications of the possible presence of such half-vortices for the properties of high temperature superconductors are discussed.

cond-mat↗