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Pavol VALKO Dept. of Physics, Slovak Technical University Il kovi čova 3, 812 19 Bratislava

Critical review of experimental approach to nonclassical gravitational interactions in superconductors. Pavol VALKO Dept. of Physics, Slovak Technical University Il kovi čova 3, 812 19 Bratislava. Selected experiments.

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Pavol VALKO Dept. of Physics, Slovak Technical University Il kovi čova 3, 812 19 Bratislava

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  1. Critical review of experimental approach to nonclassical gravitational interactions in superconductors Pavol VALKO Dept. of Physics, Slovak Technical University Ilkovičova 3, 812 19 Bratislava

  2. Selected experiments • J. Tate, S. B. Felch, B. Cabrera: Determination of the Cooper-pair mass in niobiumPhysical Review B, 42 (1990) 7885 • The Gravity Probe B team: Post Flight Analysis Final Report, March 2007 • H. Hayasaka, S. Takeuchi: Anomalous Weight Reduction on a Gyroscope’s Right Rotations around the Vertical Axis on the EarthPhysical Review Letters 25(1989) 2701 • E. Podkletnov, R. Nieminen: A possibility of gravitational force shielding by bulk YBa2Cu3O7-x superconductorPhysica C 2O3 (1992) 441-444 • R.H. Koch, D.J. van Harlingen, J. Clarke: Measurements of quantum noise in resistively shunted Josephson junctionsPhysical Review B , 26 (1982) 74

  3. J. Tate, S. B. Felch, B. Cabrera: Phys. Rev. B, 42 (1990) 7885 • Prediction • Cooper mass smaller than 2me by 8 ppm • Result • measured 84 ppm larger than 2me • with 21 ppm accuracy (5 ppm statistical) • Just comment • measured effect is only ~4.5 s • with new Planck constant value (NIST) • used value h=6.626 075 5(40)x10-34J.s • current NIST value h=6.626 068 96(33)x10-34J.s • the result should be 83 ± 20 ppm (small change but...)

  4. J. Tate, S. B. Felch, B. Cabrera: Phys. Rev. B, 42 (1990) 7885 • experimental “nightmare” • electrostatic charging of the rotor • “It proved impossible to ground the rotor continuously.” • “The charge build up over the period of hours and discharged somewhat over a period of days if the rotor was not spun.” • (accumulation of charge in weak spots - patches?) • “Once the rotor was coated with a thin metallic film, the sign of d reversed but then gradually (over weeks) headed towards zero, and became positive again.” • in experiment d varied between +0.0025 and -0.003

  5. J. Tate, S. B. Felch, B. Cabrera: Phys. Rev. B, 42 (1990) 7885 • To keep in mind • this experiment was spin-off experiment from GPB with expected major sources of errors • rotor position shift in housing ± 16 ppm • nonuniform charge distribution in rotor ± 5 • detection loop area ± 8.86 • further possible problems discussed in paper • vortex trapping in niobium ??? • after GPB results we know that all listed effects are important

  6. The Gravity Probe B • observed experimental “problems” • polhode motion (without periodicity pattern) • small classical torque (and associated energy dissipation) • caused by (primarily) • electrostatic patches on gyro (and housing) metal coating • niobium sputtered in 64 steps - with clearly observed effect of the last coating step • trapped flux in superconducting niobium • sputtered niobium is hard Type-II superconductor • high Tc of niobium (larger than shielding lead) • is there (any) significance of GPB observations for Tate, et al. experiment?

  7. H. Hayasaka, S. Takeuchi: Phys. Rev. Lett. 25 (1989) 2701

  8. J.M.Nitschke, P.A. WilmarthPhys. Rev. Lett. 64 (1990) 2115

  9. J.E. Faller et al.Phys. Rev. Lett. 64 (1990) 825

  10. E. Podkletnov, R. Nieminen: Physica C 2O3 (1992) 441-444 • weak but clearly detectable shielding effect against the gravitational force at the temperatures from 20 to 70 K • the sample with the initial weight of 5.47834 g was found to loose about 0.05% of its weight when placed over the levitating disk without any rotation • when the rotation speed of the disk increased, the weight of the sample became unstable and gave fluctuations from -2.5 to +5.4% of the initial value • at certain speeds of rotation and at certainfrequencies of electromagnetic field in therotation magnets the weight of the sample stabilized and decreased by 0.3%. • the readings in the stable regions were recorded several times with good reproducibility

  11. N. Li et al. Physica C 281 (1997) 260 • basically identical superconductor levitation set-up • different acceleration measurement method • changes in acceleration were measured to be less than 2 parts in 108 of the normal gravitational acceleration

  12. R.C. Woods et al.AIAA 2001-3363 • subset of the Podkletnov conditions examined here does not produce gravity modification measurable with our equipment (a resolution of the order of ±0.004%)

  13. Perspectives on the experimental approach currently proposed in the literature • some sources of inspiration • V. Braginsky, C.M. Caves, K.S. Thorne: Laboratory Experiments to Test Relativistic Gravity, Physical Review D 15 (1977) 2047 • J. Anandan: Relativistic Thermoelectromagnetic Gravitational Effects in Normal Conductors and Superconductors, Physics Letters 105A (1984) 280 • J. Argyris, C. Ciubotariu: A Proposal of New Gravitational Experiments, Modern Physics Letters A, 12 (1997) 3105 • C.M. Will: The Confrontation between General Relativity and Experiment, arXiv:gr-qc/0103036v1, 12 Mar 2001

  14. How to proceed (experimentally) • select the most important (or promising) effect for test • confront theoretical predictions with available experimental sensitivity • design experiment in detail • method of measurement • differential measurement if applicable • results with periodic pattern, etc. • perform experiment • at genuinely variable experimental conditions • with variable materials but identical geometry • and vice versa • cross check results via deliberately strengthening effect of major error sources

  15. Experiment to think about – part I. Cooper-pairs mass measurement • can be done (already performed) • with different superconductors (and more than one) • lead, mercury, tantalum, vanadium, bulk niobium • better experimental sensitivity • new, more sensitive DC SQUIDs are now commercially available • how to made this measurement differential? • periodic measurements in superconducting and normal state • in close vicinity of Tc (fine tuned Pb-Hg) alloys • known sources of major experimental errors • electrostatic charges(ionization will make them extreme) • flux trapping (must be tested under controlled conditions)

  16. Experiment to think about – part II.STJ noise spectrum measurement • can be done up to some frequency • maximum frequency required (2 THz) not achieved yet • various superconducting materials available • aluminum, indium, lead, tantalum, niobium • running at different temperatures experiment became semi-differential (predicted temperature behavior) • the effect of quasiparticle current shot noise must be addressed • quasiparticle sub-gap characteristics of junctions should be known prior to RSJ measurement

  17. Experiment to think about – part III.Gravitomagnetic experiments • utilizing flux interference • interference is very powerful method of measurement • since times of Michelson-Morley .... • SQUID or superfluid4He interferometer sensor • DC SQUID could be calibrated by magnetic flux • rotating superconductors (or simple superconducting current) as a source of gravitomagnetic field • magnetic vs. gravitomagnetic cross-check could be performed by shielding sensor by superconducting or usual (cryoperm) shield • in the case of quasistatic experimental set-up

  18. Experiment to think about – part IV.If I might select one • if rotating Earth is a source of gravitomagnetic field • if gravitomagnetic field causes phase shift of superconducting condensate in that case • very weak gravitomagnetic field (~10-14rad/s) • could be tested with cutting edge SQUID technology • noise better than 10-6F0(Hz)-1/2 • with ~104 m2 total SQUID input coil area • which must be sufficiently (absolutely) magnetically shielded

  19. Conclusions • there are several examples when experiments went wrong due to unknown (unclear) reasons • even the results of the best ones could be questioned • there are several (although not many) possibilities to push resolution (sensitivity) further • there are many (although unknown yet) possibilities for a “new” physics experiments using • advanced SQUIDs, superfluid4He (3He) interferometers

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