Dresden 2003 – wissenschaftliches Programm
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PV: Plenarvorträge
PV I
PV I: Plenarvortrag
Montag, 24. März 2003, 08:30–09:15, HSZ/01
SQUIDs: State-of-the-Art and Novel Applications — •John Clarke — University of California, Berkeley and Lawrence Berkeley National Laboratory, U.S.A.
SQUIDs (Superconducting QUantum Interference Devices), fabricated from either low- or high-transition temperature (Tc) superconductors for operation at liquid helium or liquid nitrogen temperatures, respectively, are exquisitely sensitive detectors of magnetic flux. Both can achieve a flux noise of the order of 10−6 flux quanta per root Hz. With appropriate input circuitry, SQUIDs can be used in a remarkably wide range of applications at frequencies ranging from 1 mHz to 1 GHz. A high-Tc SQUID microscope is used to track the motion of a single magnetotactic bacterium and is the basis of a sensitive immunoassay technique involving magnetic nanoparticles. Low-Tc SQUIDs are used to detect signals from superconducting transition-edge bolometers for submillimetre and far-infrared astronomy; a telescope with 10,000 such detectors is under construction. With an input circuit configured as a microstrip resonator, a low-Tc SQUID amplifier at 0.5 GHz is within a factor of two of the quantum limit, and is to be used in a detector to search for the axion, a candidate for cold dark matter. A low-Tc SQUID with an untuned input circuit detects ultralow frequency (< 100 Hz) nuclear magnetic resonance signals from liquids with narrow linewidths, enabling the observation of splittings due to scalar couplings of a few Hz. The same detector is used to perform magnetic resonance imaging in the kilohertz frequency range with high spatial resolution.