Perspectives in the experimental exploration of gravitational physics in superconductors

1. Perspectives in the experimental exploration of gravitational physics in superconductors Pavol VALKO Slovak Technical University Ilkovičova 3, 812 19 Bratislava

2. Basic motivation - our homes reside in the Universe - but we can see only 4 % of our home - we also believe there is some 23 % of dark matter hidden somewhere bellow our roof - and we were told there is 73 % of dark energy hanging around - therefore we would like to • learn more about our house to avoid roof damage by overweight dark “snow” • and possibly plug our appliances into dark energy power grid

3. Why superconductors? Gravitation is the weakest (known) force. Weak forces produce weak effects. BEarth 4 × 10−14rad/s Weak effects could be tested either with large sensors (to gain required sensitivity) or with very fine tools. LAGEOS, Gravity Probe B Superconducting based tools are very, very fine , while passive superconducting samples could be made also really large. DC SQUID noise level ~2.10-31 J/Hz Naturally low temperature operation required for any low noise (i.e. small signal) measurements.

4. What kind of experiments? "Classical" experiments - precision London moment experiments - to check Tate's, Cabrera result - torsion balance experiments - test of "ordinary" gravity between superconductors Novel experiments - lifetime of radioactive superconductors nuclei - Tao balls and similar "exotic" measurements - quantum interference caused by gravity related effects

5. Why to repeat "old" experiment? J. Tate, S. B. Felch, B. Cabrera: Phys. Rev. B, 42 (1990) 7885 - was a milestone experiment in relativity (gravity) related tests in superconductors - result can't be interpreted in standard physics framework - result is at the edge of acceptable precision (~4.5 ) - only one superconducting material was used (niobium) - never repeated by any other group

6. Perspectives of "classical" experiments - use of different and new superconductors • various type-I elementary superconductors to test possible material and temperature dependence of Tate's effect • middle Tc superconductor (MgB2) to test possible deviation from standard London moment behavior • torsion balance experiment with normal metal vs. superconductor effect (thermally controlled ) without any other set-up modification - more sensitive experimental set-up and sensors • new SQUID designs available fast and multi stage SQUID's • state of the art torsion balance developed Adelberger et al.

7. Perspectives of novel experiments - precise lifetime measurements of radioactive superconductors • Mössbauer effect could be used to measure mean lifetime with high precision • possible by-product of superconductor based cryogenic detectors - Tao et al., Phys. Rev. Lett. 83 (1999) 5575 - limited by optical observation - quantum interference gravitational effect - never attempted, new kind of experiments

8. Conclusions - there is no doubt that: - future experiments could significantly improve understanding of gravity related effects using superconducting experimental tools - there is a real possibility: • to prove (or disprove) existence of non-classical phenomena in superconductors - there is a fair chance: • to find evidence of interplay between macroscopic quantum systems and manifestation of yet unknown (quantum) gravity related effects