Transfer and storage of qubits in the presence of decoherence

The effects of decoherence on the transfer and storage of coherent quantum states in hybrid systems are studied within the Caldeira-Leggett approach. In general, we find that a high transfer fidelity can be achieved even if the decoherence time is less than an order of magnitude larger than the transfer time, which is approximately half a Rabi period and determined by the qubit-qubit coupling strength. Finally, we apply our results to assess the feasibility of a hybrid quantum memory system, comprised of the hyperfine qubit states of an ultracold atomic Bose-Einstein condensate and the flux qubit of a SQUID.Comment: 6 pages of EPL2, 3 figure

Tunneling into a Fractional Quantum Hall System and the Infrared Catastrophe

We calculate the tunneling density of states of a two-dimensional interacting electron gas in a quantizing magnetic field. We show that the observed pseudogap in the density of states can be understood as the result of an infrared catastrophe in a noninteracting electron model. This catastrophe stems from the response of an electronic system to the potential produced by the abruptly added charge during a tunneling event. Our formalism can be applied at any filling factor without the use of Chern-Simons or composite fermion theory