Refreshments will be served Harvard University Department of Physics Condensed Matter Physics Seminar Thursday 17 Jan 4:00pm, Lyman 425 LEV IOFFE Rutgers University "Error Correction and Topological Protection of Quantum Coherence" I compare the software approach to the error correction in quantum computation to the hardware one in which the protection from errors is due to a proper choice of the microscopic Hamiltonian. I show that devices implementing mathematical error correction at the physical level are characterized by topological order parameter. I discuss the Josephson circuits that might realize the idea of topological order parameter and thus error correction at the physical level, in particular circuits in which two protected states differ by the parity of a large integer number. Depending on implementation, this integer number can be either the number of Cooper pairs on an island or a number of fluxes in a loop. This Seminar is supported by the Harvard Quantum Optics Center [X] Joan Hamilton Faculty Assistant to Profs. Greiner & Lukin HQOC Lab Administrator HUCTW Local Union Representative 17 Oxford Street Cambridge, MA 02138 P: 617-496-2544 F: 617-496-2545