Testing Einstein´s equivalence principle at Bremen Drop Tower using LTS SQUID technique

Free fall tests to prove the Weak Equivalence Principle (WEP) were 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 WEP-proofs could be attained with torsion pendulum tests to an accuracy of 10^-12 because these pendulum tests are long term periodic experiments, Otherwise, free fall tests on Earth can be carried out only for seconds causing certain principle limitations. Nevertheless, very precise fall tests in the 10^-13 range are possible and under preparation to be carried out on Drop Tower Bremen during free fall over 109 m. A level of accuracy of 10 ^-18 will be achieved in the current STEP (Satellite Test of the Equivalence Principle) space mission of NASA/ESA. Both kinds of experiments require position detectors with an extremely high resolution to measure infinitesimal displacements of freely falling test masses. On the basis of the LTS SQUID system of the Jena University an experimental set-up was developed containing a pair of superconducting levitated test masses installed in a vacuum chamber at 4.2 K. The resolution of the SQUID position detector was measured to be as high as 4×10^-14 m/√Hz. This whole apparatus was successfully tested and dropped at the Drop Tower Bremen providing a free fall height of 109 m corresponding to a flight time of 4.7 s. Recent results of this measurements are described in this work