High Sensitive DC SQUID Based Position Detectors for Application in Gravitational Experiments at the Drop Tower Bremen

Free fall tests for proving the Weak Equivalence Principle (WEP) have been rarely be done in history. Although they seem to be the natural experiments to test the equivalence of inertial and gravitational mass, best results for proofs of the WEP could be attained with torsion pendulum tests to an accuracy of 10-12. Pendulum tests are long term periodic experiments, whereas free fall tests on Earth can be carried out only for seconds causing certain limitations in principle. Nevertheless, very precise fall tests in the 10-12 to 10-13 range are possible and under preparation to be carried out on the Drop Tower Bremen for a free fall over 110 m. These tests require position detectors with an extremely high resolution in order to measure tiny displacements of freely falling test masses. Using SQUID-based sensing technique, the displacements can be determined with an accuracy of 2 x 10-14 m/√Hz. The SQUID system, developed and manufactured at Jena University, provides high sensitivity and extremely low intrinsic noise, especially at low frequencies. Some recent results are discussed.