Research & Development

Gravitational Properties of Superconductors

Gravitational forces are believed to be some 40 orders of magnitude below their electromagnetic counterparts. That limits experiments to test Einstein’s general relativity theory to mostly astronomical observations such as light bending, the advance of Mercury’s perihelion, atomic clocks aboard sounding rockets and possibly the detection of gravitational waves using three drag-free spacecraft that are linked by laser interferometers (LISA).

In a couple of recent paper, it was suggested by M. Tajmar et al (Tajmar, M., and de Matos, C.J., Physica C, 385(4), 2003, pp. 551-554, (arxiv.org/abs/gr-qc/0203033), that a rotating superconductor might produce a so-called gravitomagnetic field many orders of magnitude larger than predicted by Einstein’s theory. This conjecture is based on the observation from Tate et al (Tate, J., Cabrera, B., Felch, S.B., Anderson, J.T., Phys. Rev. Lett. 62(8), 1989, pp. 845-848) that the magnetic field generated by a spinning superconductor, called London moment, does not fit by a factor of 5 to its prediction by quantum theory including relativistic corrections. Using this measurement one can derive the mass of the Cooper-pairs and it would appear that it is larger than two times the free electron mass. Indeed, moving matter is believed to produce a gravitomagnetic field as well (also known as the Lense-Thirring or frame-dragging effect), however, the field generated by the whole Earth is so weak that only the integration over years of orbits from the LAGEOS laser ranging satellites gave a first confirmation of this effect. Gravity Probe-B is presently mapping the Earth’s gravitomagnetic field using gyroscopes. If the gravitomagnetic field generated by matter in a coherent state such as a superconductor is now larger than what it is presently believed from the observation of normal matter such as the Earth, than this would lead to a correction factor of the London moment thus reducing the mismatch between experiment and theory.

In order to test our theory, an experimental program was established at AIT.
We concentrate on two aspects:

1. a rotating superconductor is predicted to generate a large gravitomagnetic field. This field can be directly measured using gyroscopes, similar to the approach of Gravity-Probe B.

2. A time-varying gravitomagnetic field should induce a gravitoelectric field similar to the Faraday induction law. This can be detected using very sensitive accelerometers. A short illustration is shown in Fig. 1.

Fig. 1 Gravitomagnetic and Gravitoelectric Field Generated by a Rotating and Angularly Accelerated Superconductor

A facility was constructed under contract with the US Air Force and ESA that allows rotating a superconductor ring with a diameter of 15 cm down to liquid helium temperatures with a top speed of 6500 RPM and a maximum acceleration of 1500 rad.s-2 (see Fig. 2). The sensors are mounted inside a vacuum chamber which is mechanically fixed to the roof of the building to separate it from mechanical oscillations from the rotating superconductor that are travelling through the cryostat. We use precision accelerometers and laser gyroscopes to search for any gravitational or gravitomagnetic fields present around the rotating superconductor.

Fig. 2 Experimental Assembly and Setup at AIT

First results are quite encouraging. It was observed that acceleration fields were present in the tangential direction inside and above the ring which show in the opposite direction of the applied angular acceleration (see Fig. 3). First laser gyroscope measurements also show a similar behaviour with respect to the applied angular velocity of the superconductor.

Fig. 3 Signal Averaged Accelerometer Sensor Data (■) Versus Applied Angular Acceleration (Δ)

We are presently focusing our efforts in finding the right interpretation of these data – if it is indeed due to a new gravitational/inertial effect or rather a mechanical artefact. Careful facility calibration is still on-going to further lower the noise and to remove facility artefacts.

An overview of our experimental program can be found at M. Tajmar et al, AIP Conf. Proc. 880, 1071 (2007) (arxiv.org/abs/gr-qc/0610015).

In addition, we are further refining our theoretical approach and work on other related areas in superconductivity and gravitation. Pre-prints are regularly posted on the arXiv server (www.arxiv.org).

Recent Publications:

• Tajmar, M., Plesescu, F., Seifert, B., and Marhold, K., "Measurement of Gravitomagnetic and Acceleration Fields Around Rotating Superconductors", Proceedings of the STAIF-2007 Conference, AIP Conference Proceedings, Vol. 880, 2007, pp. 1071
  
  
• Tajmar, M., "A Note on the Local cosmological constant and the dark energy coincidence problem", Classical and Quantum Gravity, Vol. 23, 2006, pp. 5079 – 5083
  
  
• Tajmar, M., Plesescu, F., Marhold, K., and De Matos, C.J., "Experimental Detection of the Gravitomagnetic London Moment", gr-qc/0603033, 2006
  
  
• De Matos, C.J., and Tajmar, M., "Gravitomagnetic London Moment and the Graviton Mass inside a Superconductor", Physica C, Vol. 432, 2005, pp. 167-172
  
  
• Tajmar, M., and De Matos, C.J., "Extended Analysis of Gravitomagnetic Fields in Rotating Superconductors and Superfluids", Physica C, Vol. 420, No. 1-2, 2005, pp. 56-60
  
  
• Tajmar, M., and de Matos, C.J., "Gravitomagnetic Field of a Rotating Superconductor and of a Rotating Superfluid", Physica C, Vol. 385, No. 4, 2003, pp. 551-554
  
  
• de Matos, C.J., Tajmar, M., "Gravitomagnetic Barnett Effect", Indian Journal of Physics, Vol. 75B, No. 5, 2001, pp. 459-461
  
  
• Tajmar, M., and de Matos, C.J., "Coupling of Electromagnetism and Gravitation in the Weak Field Approximation", Journal of Theoretics, Vol. 3, No. 1, 2001