Ultracold Atoms near superconductors and carbon nanotubes

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• Dr Jozsef Fortagh
• Tuesday 10 November 2009, 16:00-17:00
• Pippard Lecture Theatre, Cavendish Laboratory.

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The construction of hybrid quantum systems which combine ultra-cold atoms with solid state devices has attracted considerable interest in the last few years because of a number of promising applications in precision sensing and quantum information processing. I report on our experimental approach towards the realization of such systems and present measurements on ultracold atoms in the vicinity of superconducting surfaces and ultracold atoms near carbon nanotubes. The cold atom/superconductor experiment consists of a rubidium BEC apparatus and a thermally shielded helium flow cryostat at 4.2 K in the same ultrahigh vacuum system. Atom clouds are loaded into a standard magnetic microtrap formed near a superconducting niobium wire. We observe the impact of the Meissner effect on the trap parameters and measure the spin coherence time of atoms near superconductors. The coherence times are the longest yet observed in the vicinity of a highly conducting material and confirm the suppression of Johnson noise in superconductors. The results have implications for the development of coherently coupled cold atom/solid state quantum devices, in which cold atoms serve as long term quantum memory. In a second experiment, we investigate the interaction between atoms and carbon nanotubes. Free standing, single nanotubes, periodic structures, and “carpets” of nanotubes are grown on the surface of an atom chip. We describe first interaction signals between cold atoms and carbon nanotubes, in particular a non-optical measurement of the position and length of carbon nanotubes using atom clouds. In addition, we describe a novel atom detector based on field ionization of ground state atoms near carbon nanotubes and subsequent ion counting.

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