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Announcement</title></head><body>
<div>Next week's MIT QIP seminar will take place on Monday, April 11
at 16:00 in 4-237, and features:</div>
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<div align="center"><font size="+2"><b>Large-Inductance
Superconducting Flux Qubits: Coherent Oscillations and Controllable
Coupling</b></font></div>
<div><br></div>
<div align="center"><i>by</i> Prof. John Clarke (<i>U. C. Berkeley
Physics Dept.</i>)</div>
<div><br></div>
<div align="center"><u>ABSTRACT</u></div>
<div><br></div>
<blockquote>We have studied quantum coherence in a three-junction,
superconducting flux qubit using a dc SQUID to measure its flux
state. The qubit and SQUID are equipped with separate, on-chip
flux bias lines, so that we can set the flux bias of each device
independently. The chip is enclosed in a superconducting cavity,
enabling us to obtain data over several days in a stable magnetic
environment. Detailed spectroscopic measurements reveal the
expected avoided crossing at the degeneracy point, and resonances that
are ascribed to tunnel barrier defects; even at millikelvin
temperatures these resonances shift with time. The Rabi
oscillation frequency scales linearly with microwave amplitude.
The linewidth of microwave-induced resonances yields the
inhomogeneously broadened dephasing rate 1/T2', and echoes yield the
dephasing rate 1/T2; these times are consistent with the value of
1/T2* determined from Ramsey fringes. A scheme is presented for
controlling the coupling between two flux qubits by varying the
dynamic inductance of the readout SQUID surrounding them. The
mutual inductance between the qubits can be switched from zero to a
predetermined value simply by changing the bias current in the SQUID
in the zero-voltage state.</blockquote>
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