Dresden 2011 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 20: Focused Session: 50 Years of Flux Quantization
TT 20.2: Hauptvortrag
Dienstag, 15. März 2011, 11:00–11:30, HSZ 03
Fluxoid Quantization and the Superconducting Quantum Interference Device — •John Clarke — University of California, Berkeley CA USA
The observation of fluxoid quantization by Doll and Näbauer and by Deaver and Fairbank in 1961 and the observation of Josephson tunneling by Anderson and Rowell in 1963 laid the foundation for the demonstration by Jaklevic, Lambe, Silver and Mercereau in 1964 of quantum interference between two Josephson junctions interrupting a superconducting loop. Early types of SQUIDs (Superconducting Quantum Interference Devices) are briefly reviewed. Today, most SQUIDs are fabricated from thin films on silicon wafers in a square washer design, and are based on Nb-AlOx-Nb tunnel junctions. Two applications of SQUIDs are briefly described. The first is the use of a near-quantum-limited SQUID amplifier in a detector to search for the axion, a candidate particle for cold dark matter. This amplifier potentially increases the axion search rate by as much as three orders of magnitude compared with a semiconductor amplifier. The second application is the use of a SQUID to detect the signal in an ultralow field magnetic resonance imaging (ULFMRI) system operating at 5.6 kHz. At this frequency, there is a significantly higher contrast between different tissue types compared with conventional MRI. ULFMRI may have applications in imaging cancer.