Impact of the Casimir-Polder Potential and Johnson Noise on Bose-Einstein Condensate Stability Near Surfaces

Abstract

We investigate the stability of magnetically trapped atomic Bose-Einstein condensates and thermal clouds near the transition temperature at small distances 0.5 µm ≤ d ≤ 10 µm from a microfabricated silicon chip. For a 2 µm thick copper film the trap lifetime is limited by Johnson-noise induced currents and falls below 1 s at a distance of 4 µm. A dielectric surface does not adversely affect the sample until the attractive Casimir-Polder potential significantly reduces the trap depth.

Cold atoms near superconductors: atomic spin coherence beyond the Johnson noise limit

“…Since in a conservative magnetic potential, only the low-field-seeking spin states are trapped, the spin decoherence rate of atoms can be derived from measurements of the magnetic trap lifetime [5]- [7]. We apply this method for measuring the spin coherence near superconducting niobium.…”

“…Recent experiments have shown that the spin decoherence rate of atoms increases strongly when the atom cloud is trapped close to a conducting surface [5]- [8]. The measured decoherence rates are of the order of 1 s −1 at a few tens of microns from bulk metals [5,6] and about 10 s −1 near room temperature metallic thin films at micron atom-surface separations [7]. The decoherence rate decreases when the surface is cooled, as demonstrated on a 4.2 K gold thin film where rates of 0.1 s −1 have been measured for distances down to 20 µm [8].…”

“…Atomic spin decoherence near superconductors has been predicted to drop well below the Johnson noise limit of normal conductors [12] and any other experimentally relevant loss rates, such as vacuum background collisions and tunneling of atoms from the trap to the surface [7].…”

Diffuse reflection of a Bose–Einstein condensate from a rough evanescent wave mirror

“…With such a system, one can realize mirrors [6], diffraction gratings [7], 2D traps [8] or waveguides [9]. Experiments involving ultra cold atoms from a BEC at the vicinity of a dielectric surface have recently made significant progress, leading for instance to the realization of a two dimensional BEC [10], to the study of atom-surface reflection in the quantum regime [11], and to sensitive measurements of adsorbate-induced surface polarization [12] and of the Van der Waals/Casimir-Polder surface interaction [13]. .…”

Towards surface quantum optics with Bose–Einstein condensates in evanescent waves

“…However, magnetic traps are less steep than dipole traps. Therefore the problem occurs that the magnetic trapping potential is opened by the attractive Casimir-Polder potential close to surfaces which leads to the loss of atoms [18]. This can be avoided by an additional dipole potential that is generated by a blue detuned evanescent wave (Fig.1 a).…”