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Q: Quantenoptik und Photonik

Q 23: Quanteninformation II

Q 23.1: Vortrag

Dienstag, 23. März 2004, 16:30–16:45, HS 101

Quasi decoherence-free subspaces in collective quantum memories — •C. Mewes, R.G. Unanyan, and M Fleischhauer — Fachbereich Physik, Universität Kaiserslautern, 67653, Kaiserslautern, Germany

One of the most important practical challenges of quantum information processing is the protection of quantum information against decoherence. For photonic qubits stored in collective atomic superpositions [1] it can be shown that the quantum information can be protected from individual particle decoherence by combining dynamical decoupling well known in NMR systems, e.g.[2], with the concept of quasi-decoherence free subspaces. For the storage of qubits a pair of special collective states is used in which the qubit is stored in two different magnetic sublevels. Individual collisional interactions between the storage atoms itself and foreign buffer gas perturbers lead to decoherence due to spin flips and dephasing processes. By applying a fast periodic interaction it is possible to supress the dephasing mechanism. To protect the system also against spin flips an additional and sufficiently large energy gap between the two storage states and all other states has to be introdu! ced. In this way the stored qubit can be protected against decoherence from both spin flips and dephasing [3].

[1] M. Fleischhauer and M. Lukin, PRL 84 (2000) 5904

[2] U. Haeberlen and J.S. Waugh, Phys. Rev. 175 (1968) 453

[3] C. Mewes, R. Unanyan and M. Fleischhauer. To be published