arXiv subjects

Gediminas Juzeliunas

Publications and source records attributed to Gediminas Juzeliunas.

22 records · Page 2Linked to original sources

arXiv2008

Double and negative reflection of cold atoms in non-Abelian gauge potentials

Atom reflection is studied in the presence of a non-Abelian vector potential proportional to a spin-1/2 operator. The potential is produced by a relatively simple laser configuration for atoms with a tripod level scheme. We show that the atomic motion is described by two different dispersion branches with positive or negative chirality. As a consequence of that, atom reflection shows unusual features, since an incident wave may split into two reflected ones at a barrier, an ordinary specular reflection, and an additional non-specular one. Remarkably, the latter wave can exhibit negative reflection and may become evanescent if the angle of incidence exceeds a critical value. These reflection properties are crucial for future designs in non-Abelian atom optics.

cond-mat.other↗

arXiv2003

Eliminating ground-state dipole moments in quantum optics via canonical transformation

By means of a canonical transformation it is shown how it is possible to recast the equations for molecular nonlinear optics to completely eliminate ground-state static dipole coupling terms. Such dipoles can certainly play a highly important role in nonlinear optical response - but equations derived by standard methods, in which these dipoles emerge only as special cases of transition moments, prove unnecessarily complex. It has been shown that the elimination of ground-state static dipoles in favor of dipole shifts results in a considerable simplification in form of the nonlinear optical susceptibilities. In a fully quantum theoretical treatment the validity of such a procedure has previously been verified using an expedient algorithm, whose defense was afforded only by a highly intricate proof. In this paper it is shown how a canonical transformation method entirely circumvents such an approach; it also affords new insights into the formulation of quantum field interactions.

quant-ph↗

arXiv2000

Absorption by cold Fermi atoms in a harmonic trap

We study the absorption spectrum for a strongly degenerate Fermi gas confined in a harmonic trap. The spectrum is calculated using both the exact summation and also the Thomas-Fermi (TF) approximation. In the latter case, relatively simple analytical expressions are obtained for the absorption lineshape at large number of trapped atoms. At zero temperature, the approximated lineshape is characterized by a $(1-z^2)^{5/2}$ dependence which agrees well with the exact numerical calculations. At non-zero temperature, the spectrum becomes broader, although remains non-Gaussian as long as the fermion gas is degenerate. The changes in the trap frequency for an electronically excited atom can introduce an additional line broadening.

quant-ph↗

arXiv1999

Comment on "Quantum Theory of Dispersive Electromagnetic Fields"

Recently Drummond and Hillery [Phys. Rev.A 59, 691(1999)] presented a quantum theory of dispersion based on the analysis of a coupled system of the electromagnetic field and atoms in the multipolar QED formulation. The theory has led to the explicit mode-expansions for various field-operators in a homogeneous medium characterized by an arbitrary number of resonant transitions with different frequencies. In this Comment, we drawn attention to a similar multipolar study by Juzeliunas [Phys. Rev.A 53, 3543 (1996); 55, 929 (1997)] on the field quantization in a discrete molecular (or atomic) medium. A comparative analysis of the two approaches is carried out, highlighting both common and distinctive features.

quant-ph↗