arXiv subjects

G. Juzeliūnas

Publications and source records attributed to G. Juzeliūnas.

18 recordsLinked to original sources

arXiv2026

Optical creation of dark-bright soliton lattices in one-dimensional multicomponent Bose-Einstein condensates

We present a widely accessible and experimentally realizable technique for the controlled creation of dark-bright solitons and soliton lattices in one-dimensional atomic Bose-Einstein condensates. The method is based on preparing the condensate in a dark state of a $Λ$-coupled three-level system. Numerical simulations of the corresponding two-component system reveal that individual dark-bright solitons created through this scheme can survive over experimentally accessible timescales, even when the coupling laser fields are switched off. Meanwhile, the fate of soliton lattices upon the quench of the fields depends on the scattering lengths. When they are all equal, the lattice is found to persist on timescales comparable to the condensate lifetime, even though the analysis of dynamical stability reveals that they possess unstable modes. In this case the resulting destabilization is not found to be detrimental, as it leads to recurrent dynamics. However, for unequal scattering lengths the lattice structure gets destroyed once the instability sets in, which happens after a few tens of milliseconds after the quench of the optical fields.

cond-mat.quant-gas↗

arXiv2025

Light-induced localized vortices in multicomponent Bose-Einstein condensates

We study continuous interaction of a trapped two-component Bose-Einstein condensate with light fields in a $Λ$-type configuration. Using light beams with orbital angular momentum, we theoretically show how to create a stable, pinned vortex configuration, where the rotating component is confined to the region surrounded by the second, non-rotating component. The atoms constituting this vortex can be localized in volumes much smaller than the volume occupied by the second component. We also show that the vortex position can be changed dynamically by moving the laser beams, provided the beams' movement speed remains below the speed of sound. This allows us to use the localized vortex to stir the second component, and to determine the superfluid flow's critical velocity.

cond-mat.quant-gas↗

arXiv2022

One- and two-axis squeezing via laser coupling in an atomic Fermi-Hubbard model

We study a production of spin-squeezed states with ultra-cold atomic fermions described by the Fermi-Hubbard model in the Mott insulating phase. We show activation of two twisting mechanisms by a position-dependent laser coupling between internal degrees of freedom of atoms. A single laser coupling simulates the one-axis twisting model with the orientation of the twisting axis determined by the coupling phase. Adding a second laser beam with a properly chosen phase paves the way to simulate the two-axis counter-twisting model, enabling to approach the Heisenberg-limited level of squeezing.

cond-mat.quant-gas↗

arXiv2021

Optical lattice with spin-dependent sub-wavelength barriers

We analyze a tripod atom light coupling scheme characterized by two dark states playing the role of quasi-spin states. It is demonstrated that by properly configuring the coupling laser fields, one can create a lattice with spin-dependent sub-wavelength barriers. This allows to flexibly alter the atomic motion ranging from atomic dynamics in the effective brick-wall type lattice to free motion of atoms in one dark state and a tight binding lattice with a twice smaller periodicity for atoms in the other dark state. Between the two regimes, the spectrum undergoes significant changes controlled by the laser fields. The tripod lattice can be produced using current experimental techniques. The use of the tripod scheme to create a lattice of degenerate dark states opens new possibilities for spin ordering and symmetry breaking.

quant-ph↗

arXiv2019

Realization of a fractional period adiabatic superlattice

We propose and realize a deeply sub-wavelength optical lattice for ultracold neutral atoms using $N$ resonantly Raman-coupled internal degrees of freedom. Although counter-propagating lasers with wavelength $λ$ provided two-photon Raman coupling, the resultant lattice-period was $λ/2N$, an $N$-fold reduction as compared to the conventional $λ/2$ lattice period. We experimentally demonstrated this lattice built from the three $F=1$ Zeeman states of a $^{87}{\rm Rb}$ Bose-Einstein condensate, and generated a lattice with a $λ/6= 132\ {\rm nm}$ period from $λ=790 \ {\rm nm}$ lasers. Lastly, we show that adding an additional RF coupling field converts this lattice into a superlattice with $N$ wells uniformly spaced within the original $λ/2$ unit cell.

cond-mat.quant-gas↗

arXiv2019

Larkin-Ovchinikov superfluidity in time-reversal symmetric bilayer Fermi gases

Larkin-Ovchinnikov (LO) state which combines the superfluidity and spatial periodicity of pairing order parameter and exhibits the supersolid properties has been attracting intense attention in both condensed matter physics and ultracold atoms. Conventionally, realization of LO state from an intrinsic s-wave interacting system necessitates to break the time-reversal (TR) and sometimes spatial-inversion (SI) symmetries. Here we report a novel prediction that the LO state can be realized in a TR and SI symmetric system representing a bilayer Fermi gas subjected to a laserassisted interlayer tunneling. We show that the intralayer s-wave atomic interaction acts effectively like a p-wave interaction in the pseudospin space. This provides distinctive pairing effects in the present system with pseudspin spin-orbit coupling, and leads to a spontaneous density-modulation of the pairing order predicted in a very broad parameter regime. Unlike the conventional schemes, our results do not rely on the spin imbalance or external Zeeman fields, showing a highly feasible way to observe the long-sought-after LO superfluid phase using the laser-assisted bilayer Fermi gases.

cond-mat.quant-gas↗

arXiv2018

Nonlinear quantum optics for spinor slow light

We investigate quantum nonlinear effects at a level of individual quanta in a double tripod atom-light coupling scheme involving two atomic Rydberg states. In such a scheme the slow light coherently coupled to strongly interacting Rydberg states represents a two-component or spinor light. The scheme provides additional possibilities for the control and manipulation of light quanta. A distinctive feature of the proposed setup is that it combines the spin-orbit coupling for the spinor slow light with an interaction between the photons, enabling generation of the second probe beam even when two-photon detuning is zero. Furthermore, the interaction between the photons can become repulsive if the one-photon detunings have opposite signs. This is different from a single ladder atom-light coupling scheme, in which the interaction between the photons is attractive for both positive and negative detunings, as long as the Rabi frequency of the control beam is not too large.

quant-ph↗

arXiv2017

Electromagnetically induced transparency and nonlinear pulse propagation in a combined tripod and $Λ$ atom-light coupling scheme

We consider propagation of a probe pulse in an atomic medium characterized by a combined tripod and Lambda ($Λ$) atom-light coupling scheme. The scheme involves three atomic ground states coupled to two excited states by five light fields. It is demonstrated that dark states can be formed for such an atom-light coupling. This is essential for formation of the electromagnetically induced transparency (EIT) and slow light. In the limiting cases the scheme reduces to conventional $Λ$- or $N$-type atom-light couplings providing the EIT or absorption, respectively. Thus the atomic system can experience a transition from the EIT to the absorption by changing the amplitudes or phases of control lasers. Subsequently the scheme is employed to analyze the nonlinear pulse propagation using the coupled Maxwell-Bloch equations. It is shown that generation of stable slow light optical solitons is possible in such a five-level combined tripod and $Λ$ atomic system.

quant-ph↗

arXiv2017

Fulde-Ferrell-Larkin-Ovchinnikov state to topological superfluidity transition in bilayer spin-orbit coupled degenerate Fermi gas

Recently a scheme has been proposed for generating the 2D Rashba-type spin-orbit coupling (SOC) for ultracold atomic bosons in a bilayer geometry [S.-W. Su et al, Phys. Rev. A \textbf{93}, 053630 (2016)]. Here we investigate the superfluidity properties of a degenerate Fermi gas affected by the SOC in such a bilayer system. We demonstrate that a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state appears in the regime of small to moderate atom-light coupling. In contrast to the ordinary SOC, the FFLO state emerges in the bilayer system without adding any external fields or spin polarization. As the atom-light coupling increases, the system can transit from the FFLO state to a topological superfluid state. These findings are also confirmed by the BdG simulations with a weak harmonic trap added.

cond-mat.quant-gas↗

arXiv2017

Omnidirectional spin Hall effect in a Weyl spin-orbit coupled atomic gas

We show that in the presence of a three-dimensional (Weyl) spin-orbit coupling, a transverse spin current is generated in response to either a constant spin-independent force or a time-dependent Zeeman field in an arbitrary direction. This effect is the non-Abelian counterpart of the universal intrinsic spin Hall effect characteristic to the two-dimensional Rashba spin-orbit coupling. We quantify the strength of such an omnidirectional spin Hall effect by calculating the corresponding conductivity for fermions and non-condensed bosons. The absence of any kind of disorder in ultracold-atom systems makes the observation of this effect viable.

cond-mat.quant-gas↗

arXiv2017

Creation of two-photon states via interactions between Rydberg atoms during light storage

We propose a new method to create two-photon states in a controllable way using interaction between the Rydberg atoms during the storage and retrieval of slow light. A distinctive feature of the suggested procedure is that the slow light is stored into a superposition of two atomic coherences under conditions of electromagnetically induced transparency (EIT). Interaction between the atoms during the storage period creates entangled pairs of atoms in a superposition state that is orthogonal to the initially stored state. Restoring the slow light from this new atomic state one can produce a two photon state with a second-order correlation function determined by the atom-atom interaction and the storage time. Therefore the measurement of the restored light allows one to probe the atom-atom coupling by optical means with a sensitivity that can be increased by extending the storage time. As a realization of this idea we consider a many-body Ramsey-type technique which involves pi/2 pulses creating a superposition of Rydberg states at the beginning and the end of the storage period. In that case the regenerated light is due to the resonance dipole-dipole interaction between the atoms in the Rydberg states.

quant-ph↗

arXiv2016

Subwavelength-width optical tunnel junctions for ultracold atoms

We propose a new method for creating far-field optical barrier potentials for ultracold atoms with widths that are narrower than the diffraction limit and can approach tens of nanometers. The reduced widths stem from the nonlinear atomic response to control fields that create spatially varying dark resonances. The subwavelenth barrier is the result of the geometric scalar potential experienced by an atom prepared in such a spatially varying dark state. The performance of this technique, as well as its applications to the study of many-body physics and to the implementation of quantum information protocols with ultracold atoms, are discussed, with a focus on the implementation of tunnel junctions.

cond-mat.quant-gas↗

arXiv2016

Motion of solitons in one-dimensional spin-orbit-coupled Bose-Einstein condensates

Solitons play a fundamental role in dynamics of nonlinear excitations. Here we explore the motion of solitons in one-dimensional uniform Bose-Einstein condensates subjected to a spin-orbit coupling (SOC). We demonstrate that the spin dynamics of solitons is governed by a nonlinear Bloch equation. The spin dynamics influences the orbital motion of the solitons leading to the spin-orbit effects in the dynamics of the macroscopic quantum objects (mean-field solitons). The latter perform oscillations with a frequency determined by the SOC, Raman coupling, and intrinsic nonlinearity. These findings reveal unique features of solitons affected by the SOC, which is confirmed by analytical considerations and numerical simulations of the underlying Gross-Pitaevskii equations.

cond-mat.quant-gas↗

arXiv2015

Three-level Haldane-like model on dice optical lattice

We consider ultracold atoms in a two-dimensional optical lattice of the dice geometry in a tight-binding regime. The atoms experience a laser-assisted tunneling between the nearest neighbour sites of the dice lattice accompanied by the momentum recoil. This allows one to engineer staggered synthetic magnetic fluxes over plaquettes, and thus pave a way towards a realization of topologically nontrivial band structures. In such a lattice the real-valued next-neighbour transitions are not needed to reach a topological regime. Yet, such transitions can increase a variety of the obtained topological phases. The dice lattice represents a triangular Bravais lattice with a three-site basis consisting of a hub site connected to two rim sites. As a consequence, the dice lattice supports three dispersion bands. From this point of view, our model can be interpreted as a generalization of the paradigmatic Haldane model which is reproduced if one of the two rim sub-lattices is eliminated. We demonstrate that the proposed upgrade of the Haldane model creates a significant added value, including an easy access to topological semimetal phases relying only on the nearest neighbour coupling, as well as enhanced topological band structures featuring Chern numbers higher than one. The numerical investigation is supported and complemented by an analytical scheme based on the study of singularities in the Berry connection.

cond-mat.quant-gas↗

arXiv2015

Tunneling-assisted Spin-orbit Coupling in Bilayer Bose-Einstein Condensates

Motivated by a goal of realizing spin-orbit coupling (SOC) beyond one-dimension (1D), we propose and analyze a method to generate an effective 2D SOC in bilayer BECs with laser-assisted inter-layer tunneling. We show that an interplay between the inter-layer tunneling, SOC and intra-layer atomic interaction can give rise to diverse ground state configurations. In particular, the system undergoes a transition to a new type of stripe phase which spontaneously breaks the time-reversal symmetry. Different from the ordinary Rashba-type SOC, a fractionalized skyrmion lattice emerges spontaneously in the bilayer system without external traps. Furthermore, we predict the occurrence of a tetracritical point in the phase diagram of the bilayer BECs, where four different phases merge together. The origin of the emerging different phases is elucidated.

cond-mat.quant-gas↗

arXiv2015

Position-dependent spin-orbit coupling for ultracold atoms

We theoretically explore atomic Bose-Einstein condensates (BECs) subject to position-dependent spin-orbit coupling (SOC). This SOC can be produced by cyclically laser coupling four internal atomic ground (or metastable) states in an environment where the detuning from resonance depends on position. The resulting spin-orbit coupled BEC phase-separates into domains, each of which contain density modulations - stripes - aligned either along the x or y direction. In each domain, the stripe orientation is determined by the sign of the local detuning. When these stripes have mismatched spatial periods along domain boundaries, non-trivial topological spin textures form at the interface, including skyrmions-like spin vortices and anti-vortices. In contrast to vortices present in conventional rotating BECs, these spin-vortices are stable topological defects that are not present in the corresponding homogenous stripe-phase spin-orbit coupled BECs.

cond-mat.quant-gas↗

arXiv2014

Superluminal two-color light in multiple Raman gain medium

We investigate theoretically the formation of two-component light with superluminal group velocity in a medium controlled by four Raman pump fields. In such an optical scheme only a particular combination of the probe fields is coupled to the matter and exhibits superluminal propagation, the orthogonal combination is uncoupled. The individual probe fields do not have a definite group velocity in the medium. Calculations demonstrate that this superluminal component experiences an envelope advancement in the medium with respect to the propagation in vacuum.

quant-ph↗

arXiv2012

Flux lattices reformulated

We theoretically explore the optical flux lattices produced for ultra-cold atoms subject to laser fields where both the atom-light coupling and the effective detuning are spatially periodic. We analyze the geometric vector potential and the magnetic flux it generates, as well as the accompanying geometric scalar potential. We show how to understand the gauge-dependent Aharonov-Bohm singularities in the vector potential, and calculate the continuous magnetic flux through the elementary cell in terms of these singularities. The analysis is illustrated with a square optical flux lattice. We conclude with an explicit laser configuration yielding such a lattice using a set of five properly chosen beams with two counterpropagating pairs (one along the x axes and the other y axes), together with a single beam along the z axis. We show that this lattice is not phase-stable, and identify the one phase-difference that affects the magnetic flux. Thus armed with realistic laser setup, we directly compute the Chern number of the lowest Bloch band to identify the region where the non- zero magnetic flux produces a topologically non-trivial band structure.

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