Critical review of experimental approach to nonclassical

gravitational interactions in superconductors

Pavol VALKODept. of Physics, Slovak Technical University

Ilkovičova 3, 812 19 Bratislava

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

Selected experiments

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)x10-34 J.s current NIST value h=6.626 068 96(33)x10-34 J.s

◦ the result should be 83 ± 20 ppm (small change but...)

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

J. Tate, S. B. Felch, B. Cabrera: Phys. Rev. B, 42 (1990) 7885

N

S

d

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

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?

The Gravity Probe B

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

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

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

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

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

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%)

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

Perspectives on the experimental approach currently proposed in the literature

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

How to proceed (experimentally)

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)

Experiment to think about – part I. Cooper-pairs mass 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

Experiment to think about – part II.STJ noise spectrum measurement

utilizing flux interference ◦ interference is very powerful method of measurement since times of Michelson-Morley ....

SQUID or superfluid 4He 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

Experiment to think about – part III.Gravitomagnetic experiments

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 (~10-14 rad/s)◦ could be tested with cutting edge SQUID technology noise better than 10-6 0(Hz)-1/2

◦with ~104 m2 total SQUID input coil area which must be sufficiently (absolutely) magnetically shielded

Experiment to think about – part IV.If I might select one

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, superfluid 4He (3He) interferometers

Conclusions