Manifestation of the van der Waals surface interaction in the spontaneous emission of atoms into an optical nanofiber

We study the spontaneous emission of atoms near an optical nanofiber and analyze the coupling efficiency of the spontaneous emission into a nanofiber. We also investigate the influence of the van der Waals interaction of atoms with the surface of the optical nanofiber on the spectrum of coupled light. Using, as an example, Rb-85 atoms we show that the van der Waals interaction may considerably extend the red wing of the spontaneous emission line and, accordingly, produce a well-defined asymmetry of the spontaneous emission spectrum coupled into an optical nanofiber

Doppler cooling with coherent trains of laser pulses and tunable "velocity comb"

We explore the possibility of decelerating and Doppler cooling of an ensemble of two-level atoms by a coherent train of short, non-overlapping laser pulses. We develop a simple analytical model for dynamics of a two-level system driven by the resulting frequency comb field. We find that the effective scattering force mimics the underlying frequency comb structure. The force pattern depends strongly on the ratio of the atomic lifetime to the repetition time and pulse area. For example, in the limit of short lifetimes, the frequency peaks of the optical force wash out. We show that laser cooling with pulse trains results in a "velocity comb", a series of narrow peaks in the velocity space

Atom microtraps based on near-field Fresnel diffraction

We propose and present a quantitative analysis of neutral atom microtraps based on optical near fields produced by the diffraction of a laser wave on small apertures in a thin screen. We show that near-field atom microtraps are capable of storing atoms in micron-sized regions, with estimated trap lifetimes of about 1 s, when using a moderate laser intensity of about 10 W∕cm2. The depth of the proposed Fresnel atom microtraps is about 0.1 mK. An array of such atom microtraps could have applications to site-selective manipulation of cold atoms

Theory of an optical dipole trap for cold atoms

The theory of an atom dipole trap composed of a focused, far red-detuned, trapping laser beam, and a pair of red-detuned, counterpropagating, cooling beams is developed for the simplest realistic multilevel dipole interaction scheme based on a model of a (3+5)-level atom. The description of atomic motion in the trap is based on the quantum kinetic equations for the atomic density matrix and the reduced quasiclassical kinetic equation for atomic distribution function. It is shown that when the detuning of the trapping field is much larger than the detuning of the cooling field, and with low saturation, the one-photon absorption (emission) processes responsible for the trapping potential can be well separated from the two-photon processes responsible for sub-Doppler cooling atoms in the trap. Two conditions are derived that are necessary and sufficient for stable atomic trapping. The conditions show that stable atomic trapping in the optical dipole trap can be achieved when the trapping field has no effect on the two-photon cooling process and when the cooling field does not change the structure of the trapping potential but changes only the numerical value of the trapping potential well. It is concluded that the separation of the trapping and cooling processes in a pure optical dipole trap allows one to cool trapped atoms down to a minimum temperature close to the recoil temperature, keeping simultaneously a deep potential well

Laser nanotraps and nanotweezers for cold atoms: 3D gradient dipole force trap in the vicinity of Scanning Near-field Optical Microscope tip

Using a two-dipole model of an optical near-field of Scanning Near-field Optical Microscope tip, i. e. taking into account contributions of magnetic and electric dipoles, we propose and analyze a new type of 3D optical nanotrap found for certain relations between electric and magnetic dipoles. Electric field attains a minimum value in vacuum in the vicinity of the tip and hence such a trap is quite suitable for manipulations with cold atoms.Comment: 9 pages, 6 figure

Spectral distribution of atomic fluorescence coupled into an optical nanofibre

We analyse the lineshape of the fluorescence emitted by a cloud of optically excited cold atoms and coupled into an optical nanofibre. We examine the efficiency of the fluorescence coupling and describe the asymmetry of the lineshape caused by the redshifts arising from both the van der Waals and Casimir-Polder interaction of the atoms with the surface of the optical nanofibre. We compare the contributions of the van der Waals and Casimir-Polder redshifts and show that the lineshape of the fluorescence coupled into an optical nanofibre is, basically, influenced by the van der Waals redshift and is characterized by a long tail on the red side of the spectrum. We conclude that a measurement of the lineshape of the coupled fluorescence could be used to characterize the strength of the interaction of atoms with dielectric surfaces and for the detection of atoms using nanofibres

Effect of anharmonicities in the critical number of trapped condensed atoms with attractive two-body interaction

We determine the quantitative effect, in the maximum number of particles and other static observables, due to small anharmonic terms added to the confining potential of an atomic condensed system with negative two-body interaction. As an example of how a cubic or quartic anharmonic term can affect the maximum number of particles, we consider the trap parameters and the results given by Roberts et al. [Phys. Rev. Lett. 86, 4211 (2001)]. However, this study can be easily transferred to other trap geometries to estimate anharmonic effects.Comment: Total of 5 pages, 3 figures and 1 table. To appear in Phys. Rev.

Atomic micromotion and geometric forces in a triaxial magnetic trap

Non-adiabatic motion of Bose-Einstein condensates of rubidium atoms arising from the dynamical nature of a time-orbiting-potential (TOP) trap was observed experimentally. The orbital micromotion of the condensate in velocity space at the frequency of the rotating bias field of the TOP was detected by a time-of-flight method. A dependence of the equilibrium position of the atoms on the sense of rotation of the bias field was observed. We have compared our experimental findings with numerical simulations. The nonadiabatic following of the atomic spin in the trap rotating magnetic field produces geometric forces acting on the trapped atoms.Comment: 4 pages, 4 figure

Focusing of atoms with strongly confined light potentials

Focusing of atoms with light potentials is studied. In particular, we consider strongly confined, cylindrical symmetric potential, and demonstrate their applications in both red and blue-detuned focusing of atoms. We also study the influence of aberrations, and find that a resolution of 1 nm should in principle be possible.Comment: 23 pages, 9 figures, Submitted to Optics Communication

Steady state of atoms in a resonant field with elliptical polarization

We present a complete set of analytical and invariant expressions for the steady-state density matrix of atoms in a resonant radiation field with arbitrary intensity and polarization. The field drives the closed dipole transition with arbitrary values of the angular momenta $J_{g}$ and $J_{e}$ of the ground and excited state. The steady-state density matrix is expressed in terms of spherical harmonics of a complex direction given by the field polarization vector. The generalization to the case of broad-band radiation is given. We indicate various applications of these results.Comment: revtex, 26 pages, including 3 eps figures; PRA accepted for publication;v2 three typos are fixe