Speaker
Prof.
John Clarke
(University of California, Berkeley, and Lawrence Berkeley National Laboratory)
Description
The SQUID (Superconducting QUantum Interference Device) – a superconducting loop
containing two Josephson junctions – is an ultrasensitive detector of magnetic
flux. The principles, fabrication, and operation of the SQUID are outlined. With
the aid of a superconducting flux transformer, the SQUID achieves a magnetic field
noise of
10-15 T Hz-1/2; it can also be configured as a voltmeter with a noise of 10-15 V Hz-
1/2. Applications of SQUIDs – ranging from geophysics to medicine and from
nondestructive evaluation to quantum computing – are briefly reviewed. Two other
applications are discussed in more detail. The first is a SQUID as a near-quantum-
limited amplifier in the 1-GHz frequency range. This device is to be installed in
the axion detector at Lawrence Livermore National Laboratory in 2006, and is
expected to increase the frequency scan rate by three orders of magnitude. In the
second example, a SQUID is used to acquire magnetic resonance images at 5.6 kHz,
four orders of magnitude lower than in conventional MRI systems. Images of
phantoms and of the human forearm are presented, enhanced contrast due to weighting
by the longitudinal relaxation time is illustrated, and the ability to obtain
undistorted images in the presence of metals is demonstrated. Potential clinical
applications are discussed.
Author
Prof.
John Clarke
(University of California, Berkeley, and Lawrence Berkeley National Laboratory)
