II. Applications of the Josephson Effect
II. Applications of the Josephson Effect
II. Applications of the Josephson Effect
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R. Gross, A. Marx, and F. Deppe © Wal<strong>the</strong>r-Meißner-Institut (2001 - 2013)<br />
AS-Chap. 4 - 29<br />
4.1.5 Read-Out Schemes<br />
• flux-locked loop operation<br />
- hVi(F ext ) curve is nonlinear<br />
- linearization by feedback circuit<br />
linear input – output relation<br />
- oscillating flux, amplitude F 0 /2<br />
- f mod ≈ 100 kHz – several MHz<br />
• quasistatic flux = nF 0 : rectified input<br />
2f mod component<br />
lock-in detection at f mod zero<br />
• quasistatic flux = (n+1/4) F 0 :<br />
maximum lock-in output signal<br />
• detection <strong>of</strong> ac voltage:<br />
cooled transformer:<br />
SQUID impedance matching:<br />
R d N 2 R d<br />
low-noise preamplifier
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