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arXiv:quant-ph/0609158 · Physical Review A

Decay processes in the presence of thin superconducting films

Per Kristian Rekdal, Bo-Sture Skagerstam

Published Feb 27, 2007• 6 citations
arXivHTMLPDF

Abstract

In a recent paper [Phys. Rev. Lett. 97, 070401 (2006)] the transition rate of magnetic spin-flip of a neutral two-level atom trapped in the vicinity of a thick superconducting body was studied. In the present paper we will extend these considerations to a situation with an atom at various distances from a dielectric film. Rates for the corresponding electric dipole-flip transition will also be considered. The rates for these atomic flip transitions can be reduced or enhanced, and in some situations they can even be completely suppressed. For a superconducting film or a thin film of a perfect conducting material various analytical expressions are derived that reveals the dependence of the physical parameters at hand.

DOI
10.1103/physreva.75.022904

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In a recent paper [Phys. Rev. Lett. 97, 070401 (2006)] the transition rate of magnetic spin-flip of a neutral two-level atom trapped in the vicinity of a thick superconducting body was studied. In the present paper we will extend these considerations to a situation with an atom at various distances from a dielectric film. Rates for the corresponding electric dipole-flip transition will also be considered. The rates for these atomic flip transitions can be reduced or enhanced, and in some situations they can even be completely suppressed. For a superconducting film or a thin film of a perfect conducting material various analytical expressions are derived that reveals the dependence of the physical parameters at hand.
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. Vuleti\ifmmode \acute{c}\else \'{c}\fi{} [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.
Using a consistent quantum-mechanical treatment for the electromagnetic radiation, we theoretically investigate the magnetic spin-flip scatterings of a neutral two-level atom trapped in the vicinity of a superconducting body. We derive a simple scaling law for the corresponding spin-flip lifetime for such an atom trapped near a superconducting thick slab. For temperatures below the superconducting transition temperature Tc, the lifetime is found to be enhanced by several orders of magnitude in comparison to the case of a normal conducting slab. At zero temperature the spin-flip lifetime is given by the unbounded free-space value.
Using a consistent quantum-mechanical treatment for the electromagnetic radiation, we theoretically investigate the magnetic spin-flip scatterings of a neutral two-level atom trapped in the vicinity of a superconducting body. We derive a simple scaling law for the corresponding spin-flip lifetime for such an atom trapped near a superconducting thick slab. For temperatures below the superconducting transition temperature T_c, the lifetime is found to be enhanced by several orders of magnitude in comparison to the case of a normal conducting slab. At zero temperature the spin-flip lifetime is given by the unbounded free-space value.
The aim of this thesis is to investigate the interaction of neutral atoms with conducting and superconducting surfaces. Experimental advances in the magnetic confinement of ultracold atoms have shown that they can act as a powerful tool in a wide range of phenomena such as electric and magnetic field imaging and matter wave interferometry. Coherent manipulation of atoms and ever smaller magnetic traps are essential elements in the implementation of integrated quantum devices for fundamental research, quantum information processing and precision measurements. This thesis considers main influences on atoms placed within three different environments which are useful in achieving miniaturization and efficient control in atomic magnetic traps: carbon nanotubes, dielectric surfaces and superconducting thin films. The possibility of holding atoms near the outside of a carbon nanotubes will be addressed. In order to give a qualitative analysis of the atom-nanotube interaction, thermally induced spin-flips and the Casimir-Polder potential have been considered. The comparison between these two effects is presented in this thesis. It indicates that the Casimir-Polder force is the dominant loss mechanism and an estimation of the minimum trapping distance is given based on its effect. Secondly, a first-principles derivation of spatial atomic-sublevel decoherence near dielectric and metallic surfaces will be presented. The rate obtained for the decay of spatial coherence has dual implications, on one hand, it can be considered as a measure of the coherence length of the fluctuations of the electromagnetic field arising from a given substrate. On the other hand, it turns out to be relevant for quantum information encoding in double well potentials. Finally, the known spin-flip transition rate will be linked to the flux noise spectrum in superconducting thin films showing the feasibility of using cold atomic clouds in the investigation of vortex dynamics.
We study the photon emission due to a magnetic spin-flip transition of a two-level atom in the vicinity of a dielectric body such as a normal conducting metal or a superconductor. For temperatures below the transition temperature Tc{T}_{c}Tc​ of a superconductor, the corresponding spin-flip lifetime is boosted by several orders of magnitude as compared to the case of a normal conducting body. Numerical results of an exact formulation are also compared to a previously derived approximative analytical expression for the spin-flip lifetime, and we find excellent agreement. We present results on how the spin-flip lifetime depends on the temperature TTT of a superconducting body as well as its thickness HHH. Finally, we study how nonmagnetic impurities as well as possible Eliashberg strong-coupling effects influence the spin-flip rate. It is found that nonmagnetic impurities as well as strong-coupling effects have no dramatic impact on the spin-flip lifetime.
We derive a general expression for the spin-flip rate of an atom trapped near an arbitrary dielectric body and we apply this theory to the case of a two-layer cylindrical metal wire. The spin-flip lifetimes we calculate are compared with those expected for an atom near a metallic slab and with those measured by Jones et al. above a two-layer wire [M.P.A. Jones, C.J. Vale, D. Sahagun, B.V. Hall, and E.A. Hinds, Phys. Rev. Lett. 91, 080401 (2003)]. We investigate how the lifetime depends on the skin depth of the material and on the scaling of the dimensions. This leads us to some conclusions about the design of integrated circuits for manipulating ultracold atoms (atom chips).