Surface Trap for Cs atoms based on Evanescent-Wave Cooling

Abstract

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...

Stochastic rainbow caustic observed with cold atoms

“…In this Letter we report on our observation of a new type of rainbow caustic existing by virtue of a stochastic process, which distributes a singlevalued "impact parameter" over a range of "scattering angles". To our knowledge, such stochastic caustics have not been observed before.We have observed this caustic in the vertical velocity distribution of cold atoms, after bouncing inelastically off an evanescent-wave mirror [5][6][7][8]. Previous experiments on the transverse velocity distribution of atoms bouncing elastically on corrugated mirrors [9,10] also allow an interpretation in terms of caustics.…”

“…We have observed this caustic in the vertical velocity distribution of cold atoms, after bouncing inelastically off an evanescent-wave mirror [5][6][7][8]. Previous experiments on the transverse velocity distribution of atoms bouncing elastically on corrugated mirrors [9,10] also allow an interpretation in terms of caustics.…”

Thermodynamics of a multicomponent-atom sample in a tightly compressed atom trap

“…This method can be applied if the cooling efficiency does not change in the presence of the subtrap and if the cooled sample can reach thermal equilibrium before the cooling mechanisms are switched off. These conditions can be satisfied, e.g., in evanescent-wave cooling of atoms in a GOST [12,[15][16][17][18]. In fact, a "dimple" subtrap created in a GOST with an infrared focused laser beam is frequently employed [12,15].…”

“…Such a chip could contain not only magnetic microtraps, but also static electric or all-optical traps. If, for instance, the chip substrate is made of material which is transparent to light, a gravito-optical surface trap [16][17][18] could serve as a container of cold atoms and as a trap to be modified locally.…”

Coherent manipulation of atoms by copropagating laser beams

“…In fact the earliest proposal of a surface trap for neutral atoms was a light dipole trap based on a superposition of two evanescent light waves of different frequencies [11]. The first observation of atoms cooled in an evanescent light trap was made in 1997 [12] after the cooling mechanism of atoms in evanescent waves became available [13]. The evanescent light wave traps are still under development and a recent result is that BEC Cs atoms have been produced in such a trap [14], this was not possible in magnetic traps due to specific properties of collisions between cold Cs atoms.…”