München 2004 – wissenschaftliches Programm

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Q: Quantenoptik und Photonik

Q 22: Poster Quanteninformation, -kommunikation und -computer

Q 22.8: Poster

Dienstag, 23. März 2004, 14:00–16:00, Schellingstr. 3

Decoherence suppression in collective quantum memories — •C. Mewes, R.G. Unanyan, and M Fleischhauer — Fachbereich Physik, Universität Kaiserslautern, 67653, Kaiserslautern, Germany

An important question when discussing the application of many-atom systems to quantum memory is sensitivity to errors and the question how to suppress decoherence mechanisms. It is shown that photonic qubits stored in collective atomic excitations can be protected from decoherence by creating quasi-decoherence free subspaces. Instead of assuming very special, highly symmetric interactions between the atoms and its environment, individual and independent reservoir couplings are considered. For storage of qubits a pair of special collective states are used whose probability for decoherence-induced transitions due to single atom errors scales with the inverse of the total number of atoms. By introducing a sufficiently large energy gap between these two storage states and all other states a quasi-decoherence free subspace for the stored qubit is created which protects the storage state against decoherence from spin flips. To supress additional dephasing mechanisms an additional ! fast periodic interaction, well known in NMR schemes, is discussed.