Atomic spin decoherence near conducting and superconducting films

We derive scaling laws for the spin decoherence of neutral atoms trapped near conducting and superconducting plane surfaces. A result for thin films sheds light on the measurement of Y. J. Lin, I. Teper, C. Chin, and V. Vuletic [Phys. Rev. Lett. 92, 050404 (2004)]. Our calculation is based on a quantum-theoretical treatment of electromagnetic radiation near metallic bodies [P. K. Rekdal, S. Scheel, P. L. Knight, and E. A. Hinds, Phys. Rev. A 70, 013811 (2004)]. We show that there is a critical atom-surface distance that maximizes the spin relaxation rate and we show how this depends on the skin depth and thickness of the metal surface. In the light of this impedance-matching effect we discuss the spin relaxation to be expected above a thin superconducting niobium layer.