Large and randomly arranged pinning centers cause a strong deformation of a flux line lattice, so that each pinning center acts on the lattice with a maximum force. The average force for such single-particle pinning can be inferred from a simple summing procedure and has a domelike dependence on magnetic field. Pinning centers of average ]orce, such as clusters of dislocations, strongly deform the flux line lattice only in weak fields and in fields close to the critical field, where there is a peak in the dependence of the critical current on magnetic field. In the range of intermediate fields there is a weak collective pinning. A large concentration of weak centers leads to collective pinning in all fields. In this case, near the critical field a critical current peak should be observed. To explain this peak and to define the boundaries between the regions of collective and single-particle pinning the possible break -off of the flux line lattice from the lines of magnetic force should be taken into consideration, which leads to extra softening of the lattice. 409

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We have decelerated a cesium atomic beam from thermal velocities down to several tens of m͞s within only a 10 cm slowing distance. A bichromatic standing light wave was used to generate a stimulated force exceeding the spontaneous force limit by a factor of ϳ10 and extending over a large, saturation-broadened velocity range. Because of the short slowing distance this method allows production of very intense, continuous beams of slow atoms. [S0031-9007(97)

We demonstrate a gravito-optical surface trap for Cs atoms which exploits cooling in an evanescent light wave. About 10 5 atoms were cooled down to 3 mK and formed a sample with a mean height of ϳ20 mm above the surface of a dielectric prism. The trap does not use a magnetic field and leads to very small atomic level perturbations. The excited-state population of the stored atoms is ϳ1.5 3 10 26 and collisional losses are strongly suppressed. [S0031-9007(97)04024-6] PACS numbers: 32.80. Pj, 42.50.Vk The specular reflection of atoms from an evanescent light wave (EW), originally suggested by Cook and Hill in 1982 [1] and first observed in 1987 [2], has attracted great interest to realize mirrors, resonators, and waveguides for atoms [3].Efforts to confine the motion of atoms with the help of EW mirrors have so far focused on the conservative, i.e., nondissipative or coherent case, motivated by the possibility to construct matter-wave resonators [4,5]. Important experimental steps have been made with the observation of cold atoms bouncing in the field of gravity on a flat EW mirror [6] and with the demonstration of the confinement of atoms in a gravito-optical cavity based on a curved EW [7].Recent work has shown that the reflection of atoms from an EW can also act in a dissipative way [8-12]: Inelastic reflection processes can efficiently extract energy from the atomic motion which opens a way to cool atoms in novel gravito-optical traps with the prospect to obtain very dense samples [9,10]. Experimentally, single cooling EW reflection processes were studied with a thermal Na atomic beam at grazing incidence [11] and with a cold ensemble of Cs atoms dropped onto the EW at normal incidence [12].In this Letter, we present a novel gravito-optical surface trap (GOST) in which we use EW cooling to store an ensemble of Cs atoms closely above a flat dielectric surface. In our trap, schematically shown in Fig. 1, horizontal confinement is provided by the conservative optical dipole potential of a hollow, cylindrical laser beam, far blue detuned from the atomic resonance.The EW cooling mechanism in the GOST is based on the splitting of the 2 S 1͞2 ground state of Cs into two hyperfine sublevels with F 3, 4. Because of the much smaller hyperfine splitting of the excited 2 P 3͞2 state, we can model the atom as a three-level scheme [10] with two ground states separated by d hfs ͞2p 9.2 GHz and one excited state. The EW is linearly polarized and tuned to the blue side of both transitions with corresponding frequency detunings d F d ew (for F 3) and d F d ew 1 d hfs (for F 4). The interaction with the EW leads to light shifts of the atomic levels and thus results in repulsive ground-state potentials for the atomic motionwhich depend on the distance z from the surface and the hyperfine state F, but not on the particular magnetic substate [10]. Here G 2p 3 5.3 MHz and l 852 nm denote the natural linewidth and the wavelength of the optical transition, and I 0 and L represent the maximum intensity and the decay length of the E...

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The critical field of a thin superconducting film with a blind circular hole is found theoretically. It is shown that the value of the critical field is sensitive to the bottom thickness, but the orbital momentum, i.e., the number of vortices which nucleate inside the hole, is not sensitive. A simple boundary condition for a steplike thin film is derived and used for comparative numerical analysis of the superconductivity nucleation in a microdisk and near the hole. By increasing the thickness of the bottom of a blind hole one can transform the hole into a disk of the same radius which rests on top of the film. We show that such transformation leads to a jump in the number of vortices which nucleate at the critical magnetic field inside the perimeter of the hole ͑the disk͒. We report also the results of the Bitter decoration experiments of a thin superconducting film with a lattice of open or blind holes. It is found ͑in accordance with the calculation͒ that the bottom thickness has only a weak influence on the number of vortices captured by a hole during the cooling of the sample at a constant perpendicular magnetic field. All the experimental results are explained under the assumption that the vortices nucleated inside a hole rest inside during the cooling process and no additional vortices enter the hole.