V. E. Lembessis

Optical ferris wheel for ultracold atoms

We propose a versatile optical ring lattice suitable for trapping cold and quantum degenerate atomic samples. We demonstrate the realisation of intensity patterns from pairs of Laguerre-Gauss (exp(i??) modes with different ? indices. These patterns can be rotated by introducing a frequency shift between the modes. We can generate bright ring lattices for trapping atoms in red-detuned light, and dark ring lattices suitable for trapping atoms with minimal heating in the optical vortices of blue-detuned light. The lattice sites can be joined to form a uniform ring trap, making it ideal for studying persistent currents and the Mott insulator transition in a ring geometry.

Surface plasmon optical vortices and their influence on atoms

An optical mode is generated in vacuum by the total internal reflection of a beam, at the planar surface of a dielectric on which a metallic film is deposited. When the beam impinging on the surface is a Laguerre–Gaussian (LG) mode, the resulting surface mode with field components in the vacuum region possesses vortex properties, in addition to surface plasmon features. Such surface plasmon optical vortex (SPOV) modes have well-defined orbital angular momentum, residing in an azimuthal phase relative to the propagation direction of the internally reflected light. Significantly, as SPOVs are characterized by a small mode volume, they can strongly couple to atomic or molecular systems in the vicinity of the surface. In particular, SPOVs generated by single or counter-propagating, symmetrically incident laser fields give rise to optical forces that can restrict the lateral in-plane motion of such atoms, thus acting as a trap. Typical atom trajectories, evaluated for sodium atoms initially localized in the vicinity of the metallized surface, exhibit a variety of rotational, vibrational and translational effects, as well as trapping.

Quantum Hall physics with cold atoms in cylindrical optical lattices

We propose and study various realizations of a Hofstadter-Hubbard model on a cylinder geometry with fermionic cold atoms in optical lattices. The cylindrical optical lattice is created by copropagating Laguerre-Gauss beams, i.e.~light beams carrying orbital angular momentum. By strong focusing of the light beams we create a real space optical lattice in the form of rings, which are offset in energy. A second set of Laguerre-Gauss beams then induces a Raman-hopping between these rings, imprinting phases corresponding to a synthetic magnetic field (artificial gauge field). In addition, by rotating the lattice potential, we achieve a slowly varying flux through the hole of the cylinder, which allows us to probe the Hall response of the system as a realization of Laughlins thought experiment. We study how in the presence of interactions fractional quantum Hall physics could be observed in this setup.

A mobile atom in a Laguerre–Gaussian laser beam

Abstract We consider a mobile two-level atom interacting with a linearly polarised monochromatic coherent Laguerre–Gaussian laser beam. The electric dipole interaction should be supplemented by the so-called Roentgen term. We calculate the radiation pressure force and show that terms arise which involve the coupling of the photon angular momentum with the atomic particle angular momentum.

Doppler cooling of ion cyclotron motion in counter-propagating Laguerre-Gaussian beams

Abstract We demonstrate theoretically that ions moving in the field of two axial counter-propagating Laguerre-Gaussian (LG) light modes and a constant axial magnetic field, exhibit novel cooling effects. When the beams have orbital angular momentum l of the same sign we find that in addition to an axial force similar to the conventional plane wave Doppler cooling force, there is a velocity-independent quantised torque about the common beam axis which significantly influences the subsequent motion of the ion. The new effects are illustrated for the cooling of 24 Mg + ions in the presence of an axial magnetic field.

Artificial gauge potentials for neutral atoms: an application in evanescent light fields

We show that atoms interacting with evanescent light fields, generated at the interface of a dielectric with vacuum, experience artificial gauge potentials. Both the magnitude and the spatial distribution of these potentials depend crucially on the physical parameters that characterize the evanescent fields most notably the refractive index of the dielectric material and the angle of incidence of the laser beam totally internally reflected at the interface. Gauge fields are derived for various evanescent light fields and for both two-level and three-level systems. The use of such artificial gauge potentials for the manipulation of atoms trapped at the interfaces is pointed out and discussed.

Guiding of atoms in helical optical potential structures

The classical dynamics of a cold atom trapped inside a static helical optical potential is investigated based on the Lagrangian formalism, which takes into account both the optical light field and the gravitational field. The resulting equations of motion are solved numerically and analytically. The topology of the helical optical potential, which drives the trapped cold atom, is responsible for two different types of oscillations, namely: the local oscillations, whereby the atomic motion is confined in a region smaller than the light field wavelength and the global oscillations, when the atomic motion is extended to larger regions comparable to the beam Rayleigh range Local oscillations guide the atom along the helical structure of the optical potential. The global oscillations, which constitute the main topic of our paper, define the atomic motion along the z-axis as an oscillation between two turning points. For typical values of the beam waist the turning points are symmetrical around the origin. For large values of the beam waist the global oscillations become asymmetric because the optical dipole potential weakens and the gravitational potential contributes to the determination of the turning points. For sufficiently large values of the beam waist there are no global oscillations and only one upper turning point defines the atoms global motion.

Generation of surface optical screw dislocations by evanescent plasmonic modes

A novel form of optical screw dislocation based on localized surface-plasmon modes (SPMs) is described. In particular, we show that a metallic sheet in the form an infinitesimally thin film deposited on a planar dielectric substrate creates surface-plasmon modes due to evanescent Laguerre-Gaussian (LG) light. The characteristic property of such a mode is the exponential decay with distance normal to the interface in the vacuum region. This localized mode can be described as a surface optical screw dislocation possessing a desirable enhancement due to the localized surface plasmon content of the mode. Such a screw dislocation is controllable by changing the angle of internal reflection and the quantum numbers of the LG light.

Optical vortex singularities and atomic circulation in evanescent waves

The total internal reflection of an optical beam with a phase singularity can generate evanescent light that displays a rotational character. At a metalized surface, in particular, field components extending into the vacuum region possess vortex properties in addition to surface plasmon features. These surface plasmonic vortices retain the phase singularity of the input light, also mapping its associated orbital angular momentum. In addition to a two-dimensional patterning on the surface, the strongly localized intensity distribution decays with distance perpendicular to the film surface. The detailed characteristics of these surface optical vortex structures depend on the incident beam parameters and the dielectric mismatch of the media. The static interference of the resulting surface vortices, achieved by using beams suitably configured to restrict lateral in-plane motion, can be shown to give rise to optical forces that produce interesting dynamical effects on atoms or small molecules trapped in the vicinity of the surface. As well as trapping within the surface plasmonic fields, model calculations reveal that the corresponding atomic trajectories will typically exhibit a variety of rotational and vibrational effects, significantly depending on the extent and sign of detuning from resonance.

Radiation pattern of two identical emitters driven by a Laguerre-Gaussian beam: An atom nanoantenna

We study the directional properties of a radiation field emitted by a geometrically small system composed of two identical two-level emitters located at short distances and driven by an optical vortex beam, a Laguerre-Gaussian beam which possesses a structured phase and amplitude. We find that the system may operate as a nanoantenna for controlled and tunable directional emission. Polar diagrams of the radiation intensity are presented showing that a constant phase or amplitude difference at the positions of the emitters plays an essential role in the directivity of the emission. We find that the radiation patterns may differ dramatically for different phase and amplitude differences at the positions of the emitters. As a result the system may operate as a two- or one-sided nanoantenna. In particular, a two-sided highly focused directional emission can be achieved when the emitters experience the same amplitude and a constant phase difference of the driving field. We find a general directional property of the emitted field that when the phase differences at the positions of the emitters equal an even multiple of \pi/4, the system behaves as a two-sided antenna. When the phase difference equals an odd multiple of \pi/4, the system behaves as an one-sided antenna. The case when the emitters experience the same phase but different amplitudes of the driving field is also considered and it is found that the effect of different amplitudes is to cause the system to behave as a uni-directional antenna radiating along the interatomic axis.