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 />
4.5.4 Gravity Wave Antennas and Gravity Gradiometers<br />
topics: inertial navigation, general relativity, deviations from 1/r 2 , and gravitational waves:<br />
e.g. collapsing stars, rotating double stars<br />
expansion and contraction oscillations<br />
expected length change ¢l/l ~ 10 -19<br />
required resolution ~ 10 21<br />
resonant mass transducer<br />
displacement current<br />
antenna mK regime<br />
resolution: zero point motion<br />
quantum limited antenna<br />
typical resonance frequency: 1 kHz T< ~! ant /k B ≈ 50 nK<br />
but: increase <strong>of</strong> Q increase <strong>of</strong> effective noise temperature T eff<br />
assume: gravitational pulse, length ¿, antenna decay time Q/! ant :<br />
quantum limit (bar energy > k B T eff ) T < Q~/k B ¿<br />
for Q = 2£10 6 and ¿ = 1 ms T ≈ 20 mK<br />
quantum limited sensor is required<br />
presently: sensitivities ¢l/l ≈ 10 -18 , no gravity waves reported yet<br />
AS-Chap. 4 - 69
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