DC-SQUID based displacement sensor for a Mossbauer red-shift experiment

A superconducting quantum interference device (SQUID)-based displacement sensor with resolution up to 3*10/sup -15/ m/ square root Hz in the frequency band of 20 Hz-15 kHz is reported. The sensor monitors the Doppler modulation of gamma radiation in a gravitational red-shift experiment using the 93-keV Mossbauer resonance of /sup 67/Zn. Test results for the SQUID and the PZT transducer used in the experiment are presented. The relative statistical uncertainty in the determination of the gravitational red shift is about 3% for a one-week experiment. Preliminary results obtained with the displacement sensor show that the systematic uncertainties that are related to the Doppler motion generated by the velocity drive are negligible compared to the statistical uncertainty.<>