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 />
4.2.2 Operation and Performance <strong>of</strong> rf SQUIDs<br />
AS-Chap. 4 - 39<br />
additional topic: noise in rf-SQUIDs:<br />
- switching k = 0 k = 1: stochastic fluctuations (<strong>the</strong>rmal activation)<br />
noise in step voltage V T flux noise:<br />
noise causes finite slope <strong>of</strong> horizontal branches<br />
extrinsic noise source: preamplifier, lines T amp<br />
eff<br />
energy resolution:<br />
high frequencies (few GHz), cold amplifiers: ² ≈ 3£10 -32 J/Hz<br />
comparison:<br />
rf-SQUID: ² ≈ k B T/! rf<br />
dc-SQUID: ² ≈ k B T/! c (! c = 2¼IcR N /© 0 ≈ 100 GHz)<br />
better energy resolution <strong>of</strong> dc-SQUID because: ! c À ! rf
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