arXiv subjects

S. A. Gardiner

Publications and source records attributed to S. A. Gardiner.

At least 19 recordsLinked to original sources

arXiv2021

Roadmap on Atomtronics: State of the art and perspective

Atomtronics deals with matter-wave circuits of ultra-cold atoms manipulated through magnetic or laser-generated guides with different shapes and intensities. In this way, new types of quantum networks can be constructed, in which coherent fluids are controlled with the know-how developed in the atomic and molecular physics community. In particular, quantum devices with enhanced precision, control and flexibility of their operating conditions can be accessed. Concomitantly, new quantum simulators and emulators harnessing on the coherent current flows can also be developed. Here, we survey the landscape of atomtronics-enabled quantum technology and draw a roadmap for the field in the near future. We review some of the latest progresses achieved in matter-wave circuits design and atom-chips. Atomtronic networks are deployed as promising platforms for probing many-body physics with a new angle and a new twist. The latter can be done both at the level of equilibrium and non-equilibrium situations. Numerous relevant problems in mesoscopic physics, like persistent currents and quantum transport in circuits of fermionic or bosonic atoms, are studied through a new lens. We summarize some of the atomtronics quantum devices and sensors. Finally, we discuss alkali-earth and Rydberg atoms as potential platforms for the realization of atomtronic circuits with special features.

cond-mat.quant-gas↗

arXiv2019

Noise-Free Generation of Bright Matter-Wave Solitons

We show how access to sufficiently flexible trapping potentials could be exploited in the generation of three-dimensional atomic bright matter-wave solitons. Our proposal provides a route towards producing bright solitonic states with good fidelity, in contrast to, for example, a non-adiabatic sweeping of an applied magnetic field through a Feshbach resonance.

cond-mat.quant-gas↗

arXiv2018

An intuitive approach to structuring the three polarization components of light

This paper presents intuitive interpretations of tightly focused beams of light by drawing analogies to two-dimensional electrostatics, magnetostatics and fluid dynamics. We use a Helmholtz decomposition of the transverse polarization components in the transverse plane to introduce generalized radial and azimuthal polarization states. This reveals the interplay between transverse and longitudinal polarization components in a transparent fashion. Our approach yields a comprehensive understanding of tightly focused laser beams, which we illustrate through several insightful examples.

physics.optics↗

arXiv2018

Creating Complex Optical Longitudinal Polarization Structures

In this paper we show that it is possible to structure the longitudinal polarization component of light. We illustrate our approach by demonstrating linked and knotted longitudinal vortex lines acquired upon non-paraxially propagating a tightly focused sub-wavelength beam. Remaining degrees of freedom in the transverse polarization components can be exploited to generate customized topological vector beams.

physics.optics↗

arXiv2016

Cooperative eigenmodes and scattering in 1D atomic arrays

Collective coupling between dipoles can dramatically modify the optical response of a medium. Such effects depend strongly on the geometry of the medium and the polarization of the light. Using a classical coupled dipole model, here we investigate the simplest case of one dimensional (1D) arrays of interacting atomic dipoles driven by a weak laser field. Changing the polarization and direction of the driving field allows us to separately address superradiant, subradiant, red-shifted, and blue-shifted eigenmodes, as well as observe strong Fano-like interferences between different modes. The cooperative eigenvectors can be characterized by the phase difference between nearest neighbor dipoles, ranging from all oscillating in phase to all oscillating out of phase with their nearest neighbors. Investigating the eigenvalue behavior as a function of atom number and lattice spacing, we find that certain eigenmodes of an infinite atomic chain have the same decay rate as a single atom between two mirrors. The effects we observe provide a framework for collective control of the optical response of a medium, giving insight into the behavior of more complicated geometries, as well as providing further evidence for the dipolar analog of cavity QED.

physics.atom-ph↗

arXiv2016

Excitation of knotted vortex lines in matter waves

We study the creation of knotted ultracold matter waves in Bose-Einstein condensates via coherent two-photon Raman transitions with a $Λ$ level configuration. The Raman transition allows an indirect transfer of atoms from the internal state $\left| a \right\rangle$ to the target state $\left| b \right\rangle$ via an excited state $\left| e \right\rangle$, that would be otherwise dipole-forbidden. This setup enables us to imprint three-dimensional knotted vortex lines embedded in the the probe field to the density in the target state. We elaborate on experimental feasibility as well as on subsequent dynamics of the matter wave.

cond-mat.quant-gas↗

arXiv2016

3D quaternionic condensations, Hopf invariants, and skyrmion lattices with synthetic spin-orbit coupling

We study the topological configurations of the two-component condensates of bosons with the $3$D $\vecσ\cdot \vec{p}$ Weyl-type spin-orbit coupling subject to a harmonic trapping potential. The topology of the condensate wavefunctions manifests in the quaternionic representation. In comparison to the $U(1)$ complex phase, the quaternionic phase manifold is $S^3$ and the spin orientations form the $S^2$ Bloch sphere through the 1st Hopf mapping. The spatial distributions of the quaternionic phases exhibit the 3D skyrmion configurations, and the spin distributions possess non-trivial Hopf invariants. Spin textures evolve from the concentric distributions at the weak spin-orbit coupling regime to the rotation symmetry breaking patterns at the intermediate spin-orbit coupling regime. In the strong spin-orbit coupling regime, the single-particle spectra exhibit the Landau-level type quantization. In this regime, the three-dimensional skyrmion lattice structures are formed when interactions are below the energy scale of Landau level mixings. Sufficiently strong interactions can change condensates into spin-polarized plane-wave states, or, superpositions of two plane-waves exhibiting helical spin spirals.

cond-mat.quant-gas↗

arXiv2016

Measuring the disorder of vortex lattices in a Bose-Einstein condensate

We report observations of the formation and subsequent decay of a vortex lattice in a Bose-Einstein condensate confined in a hybrid optical-magnetic trap. Vortices are induced by rotating the anharmonic magnetic potential that provides confinement in the horizontal plane. We present simple numerical techniques based on image analysis to detect vortices and analyze their distributions. We use these methods to quantify the amount of order present in the vortex distribution as it transitions from a disordered array to the energetically favorable ordered lattice.

physics.atom-ph↗

arXiv2015

Quantum reflection of bright solitary matter-waves from a narrow attractive potential

We report the observation of quantum reflection from a narrow, attractive, potential using bright solitary matter-waves formed from a 85Rb Bose-Einstein condensate. We create narrow potentials using a tightly focused, red-detuned laser beam, and observe reflection of up to 25% of the atoms, along with the trapping of atoms at the position of the beam. We show that the observed reflected fraction is much larger than theoretical predictions for a narrow Gaussian potential well; a more detailed model of bright soliton propagation, accounting for the generic presence of small subsidiary intensity maxima in the red-detuned beam, suggests that these small intensity maxima are the cause of this enhanced reflection.

physics.atom-ph↗

arXiv2015

Sagnac Interferometry Using Bright Matter-Wave Solitons

We use an effective one-dimensional Gross-Pitaevskii equation to study bright matter-wave solitons held in a tightly confining toroidal trapping potential, in a rotating frame of reference, as they are split and recombined on narrow barrier potentials. In particular, we present an analytical and numerical analysis of the phase evolution of the solitons and delimit a velocity regime in which soliton Sagnac interferometry is possible, taking account of the effect of quantum uncertainty.

cond-mat.quant-gas↗

arXiv2015

Beyond Thomas--Fermi analysis of the density profiles of a miscible two-component Bose--Einstein condensate

We investigate a harmonically trapped two-component Bose--Einstein condensate within the miscible regime, close to its boundaries, for different ratios of effective intra- and inter-species interactions. We derive analytically a universal equation for the density around the different boundaries in one, two and three dimensions, for both the coexisting and spatially separated regimes. We also present a general procedure to solve the Thomas--Fermi approximation in all three spatial dimensionalities, reducing the complexity of the Thomas--Fermi problem for the spatially separated case in one and three dimensions to a single numerical inversion. Finally, we analytically determine the frontier between the two different regimes of the system.

cond-mat.quant-gas↗

arXiv2014

Splitting bright matter-wave solitons on narrow potential barriers: quantum to classical transition and applications to interferometry

We study bright solitons in the Gross-Pitaevskii equation as they are split and recombined in a low energy system. We present new analytic results determining the general region in which a soliton may not be split on a potential barrier, and confirm these results numerically. Furthermore, we analyse the energetic regimes where quantum fluctuations in the initial center of mass position and momentum become influential on the outcome of soliton splitting and recombination events. We then use the results of this analysis to determine a parameter regime where soliton interferometry is practicable.

cond-mat.quant-gas↗

arXiv2013

Second-order, number-conserving description of non-equilibrium dynamics in finite-temperature Bose-Einstein condensates

While the Gross--Pitaevskii equation is well-established as the canonical dynamical description of atomic Bose-Einstein condensates (BECs) at zero-temperature, describing the dynamics of BECs at finite temperatures remains a difficult theoretical problem, particularly when considering low-temperature, non-equilibrium systems in which depletion of the condensate occurs dynamically as a result of external driving. In this paper, we describe a fully time-dependent numerical implementation of a second-order, number-conserving description of finite-temperature BEC dynamics. This description consists of equations of motion describing the coupled dynamics of the condensate and non-condensate fractions in a self-consistent manner, and is ideally suited for the study of low-temperature, non-equilibrium, driven systems. The δ-kicked-rotor BEC provides a prototypical example of such a system, and we demonstrate the efficacy of our numerical implementation by investigating its dynamics at finite temperature. We demonstrate that the qualitative features of the system dynamics at zero temperature are generally preserved at finite temperatures, and predict a quantitative finite-temperature shift of resonance frequencies which would be relevant for, and could be verified by, future experiments.

cond-mat.quant-gas↗

arXiv2013

Controlled formation and reflection of a bright solitary matter-wave

Solitons are non-dispersive wave solutions that arise in a diverse range of nonlinear systems, stablised by a focussing or defocussing nonlinearity. First observed in shallow water, solitons have subsequently been studied in many other fields including nonlinear optics, biophysics, astrophysics, plasma and particle physics. They are characterised by well localised wavepackets that maintain their initial shape and amplitude for all time, even following collisions with other solitons. Here we report the controlled formation of bright solitary matter-waves, the 3D analog to solitons, from Bose-Einstein condensates of 85Rb and observe their propagation in an optical waveguide. These results pave the way for new experimental studies of bright solitary matterwave dynamics to elucidate the wealth of existing theoretical work and to explore an array of potential applications including novel interferometric devices, the study of short-range atom-surface potentials and the realisation of Schrodingercat states.

physics.atom-ph↗

arXiv2012

Equilibrium solutions of immiscible two-species Bose-Einstein condensates in perturbed harmonic traps

We investigate the mean--field equilibrium solutions for a two--species immiscible Bose--Einstein condensate confined by a harmonic confinement with additional linear perturbations. We observe a range of equilibrium density structures, including `ball and shell' formations and axially/radially separated states, with a marked sensitivity to the potential perturbations and the relative atom number in each species. Incorporation of linear trap perturbations, albeit weak, are found to be essential to match the range of equilibrium density profiles observed in a recent Rb-87 - Cs-133 Bose-Einstein condensate experiment [D. J. McCarron et al., Phys. Rev. A, 84, 011603(R) (2011)]. Our analysis of this experiment demonstrates that sensitivity to linear trap perturbations is likely to be important factor in interpreting the results of similar experiments in the future.

cond-mat.quant-gas↗

arXiv2012

Bright solitary matter waves: formation, stability and interactions

In recent years, bright soliton-like structures composed of gaseous Bose-Einstein condensates have been generated at ultracold temperature. The experimental capacity to precisely engineer the nonlinearity and potential landscape experienced by these solitary waves offers an attractive platform for fundamental study of solitonic structures. The presence of three spatial dimensions and trapping implies that these are strictly distinct objects to the true soliton solutions. Working within the zero-temperature mean-field description, we explore the solutions and stability of bright solitary waves, as well as their interactions. Emphasis is placed on elucidating their similarities and differences to the true bright soliton. The rich behaviour introduced in the bright solitary waves includes the collapse instability and symmetry-breaking collisions. We review the experimental formation and observation of bright solitary matter waves to date, and compare to theoretical predictions. Finally we discuss the current state-of-the-art of this area, including beyond-mean-field descriptions, exotic bright solitary waves, and proposals to exploit bright solitary waves in interferometry and as surface probes.

cond-mat.quant-gas↗

arXiv2012

Number-Conserving Approaches for Atomic Bose-Einstein Condensates: An Overview

Assuming the existence of a Bose-Einstein condensate composed of the majority of a sample of ultracold, trapped atoms, perturbative treatments to incorporate the non-condensate fraction are common. Here we describe how this may be carried out in an explicitly number-conserving fashion, providing a common framework for the work of various authors; we also briefly consider issues of implementation, validity and application of such methods.

cond-mat.quant-gas↗

arXiv2012

Variational determination of approximate bright matter-wave soliton solutions in anisotropic traps

We consider the ground state of an attractively-interacting atomic Bose-Einstein condensate in a prolate, cylindrically symmetric harmonic trap. If a true quasi-one-dimensional limit is realized, then for sufficiently weak axial trapping this ground state takes the form of a bright soliton solution of the nonlinear Schroedinger equation. Using analytic variational and highly accurate numerical solutions of the Gross-Pitaevskii equation we systematically and quantitatively assess how soliton-like this ground state is, over a wide range of trap and interaction strengths. Our analysis reveals that the regime in which the ground state is highly soliton-like is significantly restricted, and occurs only for experimentally challenging trap anisotropies. This result, and our broader identification of regimes in which the ground state is well-approximated by our simple analytic variational solution, are relevant to a range of potential experiments involving attractively-interacting Bose-Einstein condensates.

cond-mat.quant-gas↗