arXiv subjects

J. Ruseckas

Publications and source records attributed to J. Ruseckas.

46 records · Page 3Linked to original sources

arXiv2005

Effective magnetic fields in degenerate atomic gases induced by light beams with orbital angular momenta

We investigate the influence of two resonant laser beams on the mechanical properties of degenerate atomic gases. The control and probe beams of light are considered to have Orbital Angular Momenta (OAM) and act on the three-level atoms in the Electromagnetically Induced Transparency (EIT) configuration. The theory is based on the explicit analysis of the quantum dynamics of cold atoms coupled with two laser beams. Using the adiabatic approximation, we obtain an effective equation of motion for the atoms driven to the dark state. The equation contains a vector potential type interaction as well as an effective trapping potential. The effective magnetic field is shown to be oriented along the propagation direction of the control and probe beams containing OAM. Its spatial profile can be controlled by choosing proper laser beams. We demonstrate how to generate a constant effective magnetic field, as well as a field exhibiting a radial distance dependence. The resulting effective magnetic field can be concentrated within a region where the effective trapping potential holds the atoms. The estimated magnetic length can be considerably smaller than the size of the atomic cloud.

cond-mat.other↗

arXiv2005

Light induced effective magnetic fields for ultra-cold atoms in planar geometries

We propose a scheme to create an effective magnetic field for ultra-cold atoms in a planar geometry. The set-up allows the experimental study of classical and quantum Hall effects in close analogy to solid-state systems including the possibility of finite currents. The present scheme is an extention of the proposal in Phys. Rev. Lett. 93, 033602 (2004) where the effective magnetic field is now induced for three-level Lambda-type atoms by two counterpropagating laser beams with shifted spatial profiles. Under conditions of electromagentically induced transparency the atom-light interaction has a space dependent dark state, and the adiabatic center of mass motion of atoms in this state experiences effective vector and scalar potentials. The associated magnetic field is oriented perpendicular to the propagation direction of the laser beams. The field strength achievable is one flux quantum over an area given by the transverse beam separation and the laser wavelength. For a sufficiently dilute gas the field is strong enough to reach the lowest Landau level regime.

quant-ph↗

arXiv2005

Effective magnetic fields induced by EIT in ultra-cold atomic gases

We study the influence of two resonant laser beams (to be referred to as the control and probe beams) on the centre of mass motion of ultra-cold atoms characterised by three energy levels of the Lambda-type. The laser beams being in the Electromagnetically Induced Transparency (EIT) configuration drive the atoms to their dark states. We impose the adiabatic approximation and obtain an effective equation of motion for the dark state atoms. The equation contains a vector potential type interaction as well as an effective trapping potential. We concentrate on the situation where the control and probe beams are co-propagating and have Orbital Angular Momenta (OAM). The effective magnetic field is then oriented along the propagation direction of the control and probe beams. Its spatial profile can be shaped by choosing proper laser beams. We analyse several situations where the effective magnetic field exhibits a radial dependence. In particular we study effective magnetic fields induced by Bessel beams, and demonstrate how to generate a constant effective magnetic field for a ring geometry of the atomic trap. We also discuss a possibility to create an effective field of a magnetic monopole.

quant-ph↗

arXiv2005

Point Process Models of 1/f Noise and Internet Traffic

We present a simple model reproducing the long-range autocorrelations and the power spectrum of the web traffic. The model assumes the traffic as Poisson flow of files with size distributed according to the power-law. In this model the long-range autocorrelations are independent of the network properties as well as of inter-packet time distribution.

cs.NI↗

arXiv2005

Non-Abelian gauge potentials for ultra-cold atoms with degenerate dark states

We show that the adiabatic motion of ultra-cold, multi-level atoms in spatially varying laser fields can give rise to effective non-Abelian gauge fields if degenerate adiabatic eigenstates of the atom-laser interaction exist. A pair of such degenerate dark states emerges e.g. if laser fields couple three internal states of an atom to a fourth common one under pairwise two--photon-resonance conditions. For this so-called tripod scheme we derive general conditions for truly non-Abelian gauge potentials and discuss special examples. In particular we show that using orthogonal laser beams with orbital angular momentum an effective magnetic field can be generated that has a monopole component.

cond-mat.mes-hall↗

arXiv2004

Time problem in quantum mechanics and its analysis by the concept of weak measurement

The model of weak measurements is applied to various problems, related to the time problem in quantum mechanics. The review and generalization of the theoretical analysis of the time problem in quantum mechanics based on the concept of weak measurements are presented. A question of the time interval the system spends in the specified state, when the final state of the system is given, is raised. Using the concept of weak measurements the expression for such time is obtained. The results are applied to the tunneling problem. A procedure for the calculation of the asymptotic tunneling and reflection times is proposed. Examples for delta-form and rectangular barrier illustrate the obtained results. Using the concept of weak measurements the arrival time probability distribution is defined by analogy with the classical mechanics. The proposed procedure is suitable to the free particles and to particles subjected to an external potential, as well. It is shown that such an approach imposes an inherent limitation to the accuracy of the arrival time definition.

quant-ph↗

arXiv2004

Stochastic nonlinear differential equation generating 1/f noise

Starting from the simple point process model of 1/f noise we derive a stochastic nonlinear differential equation for the signal exhibiting 1/f noise in any desirably wide range of frequency. A stochastic differential equation (the general Langevin equation with a multiplicative noise) that gives 1/f noise is derived for the first time. The solution of the equation exhibits the power-law distribution. The process with 1/f noise is demonstrated by the numerical solution of the derived equation with the appropriate restriction of the diffusion of the signal in some finite interval.

cond-mat.stat-mech↗

arXiv2004

General expression for the quantum Zeno and anti-Zeno effects

In this paper we investigate the quantum Zeno and anti-Zeno effects without using any particular model of the measurement. Making a few assumptions about the measurement process we derive an expression for the jump probability during the measurement. From this expression the equation, obtained by Kofman and Kurizki [Nature (London) 405, 546 (2000)] can be derived as a special case.

quant-ph↗

arXiv2003

Weak measurement of arrival time

The arrival time probability distribution is defined by analogy with the classical mechanics. The difficulty of requirement to have the values of non-commuting operators is circumvented using the concept of weak measurements. The proposed procedure is suitable to the free particles and to the particles subjected to an external potential, as well. It is shown that such an approach imposes an inherent limitation to the accuracy of the arrival time determination.

quant-ph↗

arXiv2002

Time problem in quantum mechanics and weak measurements

A question of the time the system spends in the specified state, when the final state of the system is given, is raised. The model of weak measurements is used to obtain the expression for the time. The conditions for determination of such a time are obtained.

quant-ph↗