Low noise LTS SQUIDs for application in gravitational experiments

The Weak Principle of Equivalence (WEP) is proved up to now with an accuracy of 1/spl times/10/sup -12/. Short range free fall experiments attained an accuracy of 5/spl times/10/sup -10/ only. Microgravity facilities such as the "Drop Tower Bremen" enables long range free fall experiments which may improve the accuracy of free fall tests to <10/sup -12/ using high performance SQUID measuring technique. In this review the application of LTS DC SQUIDs with Nb-NbO/sub x/-Pb/In/Au window-type Josephson junctions for gravitational experiments is described. Under optimal conditions a noise limited sensitivity of 1.4/spl times/10/sup -12/ m//spl radic/(Hz) for the position detector was achieved corresponding to a flux noise of the SQUID system of 2/spl times/10/sup -6/ /spl Phi//sub 0///spl radic/(Hz). The contribution gives the design of the DC SQUID position detector and summarizes recent results of its application in gravitational experiments.