[QIP-Sem] MIT QIP Seminar Series - Hans Mooij

[Isaac Chuang]

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The MIT Quantum Information Processing Seminar Series
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Our fifth seminar of the Fall 2005 semester:

Speaker:  Hans Mooij
          Kavli Institute of Nanoscience 
          Delft University of Technology 

Time:     4:00pm (following refreshments)
Date:     Monday, October 24, 2005
Location: CUA conference room, 26-214

Title:    Superconducting flux qubits 

Abstract:

  Flux qubits are superconducting two-level systems where the states
  are characterized by opposite circulating currents in a
  superconducting loop with three Josephson junctions, to which a
  magnetic flux of half a flux quantum is applied. Excitation is
  performed by means of microwave pulses. They are studied in several
  groups, the talk will focus on recent progress in Delft. Much of the
  effort is directed towards improving coherence and fidelity of
  readout. Relaxation times are typically around 5 microseconds, while
  dephasing times vary strongly with conditions. The best achieved
  result is a spin-echo-corrected dephasing time of 4 microseconds.

  The usual readout so far was by measuring the critical current of a
  SQUID. A new dispersive method has been developed where the SQUID
  inductance is measured. This non- destructive technique now yields a
  fidelity of 87%. Further improvement seems possible. We have studied
  the coupling of a flux qubit to a harmonic oscillator, where we see
  cohrent transitions on the blue and red sidebands. We have also
  studied two coupled flux qubits and performed conditional
  spectroscopy. Further optimalization is needed (and possible) to
  realize two-qubit gates.  A new form of flux qubit based on
  phase-slip in superconducting wires will be discussed. This type may
  have advantages with respect to the 1/f noise that dominates in
  junctions qubits.

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Next: Oct 31 - Daniel Gottesman -  A Simple Proof of the Threshold for
                                   Fault-Tolerant Quantum Computation
http://qis.mit.edu
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