seminar: Quantum capacity of dephasing channels with memory
speaker: Giuliano Benenti (Università dell'Insubria)abstract: Quantum channels with memory are the natural theoretical framework for the study of any processing of quantum information in systems suffering from low frequency noise, that is, noise with correlation times longer that the time between consecutive uses of the channel. A central quantity in both classical and quantum information theory is the capacity of a noisy channel, that is, the maximum number of bits or qubits that can be reliably transmitted per channel use. In particular, quantum capacity refers to the coherent transmission of quantum information (measured in number of qubits). We show that the amount of coherent quantum information that can be reliably transmitted down a dephasing channel with memory is maximized by separable input states. In particular, we model the channel as a Markov chain or a multimode environment of oscillators. While in the first model the maximization is achieved for the maximally mixed input state, in the latter it is convenient to exploit the presence of a decoherence-protected subspace generated by memory effects. We explicitly compute the quantum channel capacity for the first model while numerical simulations suggest a lower bound for the latter. In both cases memory effects enhance the coherent information A. D'Arrigo, G. Benenti and G. Falci, quant-ph/0703014.
timetable:
Wed 28 Mar, 14:00 - 14:30, Aula Dini
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