Historical research guide · 0829 · 2022
Interaction Between Macroscopic Quantum Systems and Gravity
A. Gallerati · G. Modanese · G.A. Ummarino
In one minute
Antonio Gallerati and Giovanni Ummarino at the Politecnico di Torino, with Giovanni Modanese at the Free University of Bozen-Bolzano, review sixty years of work on one question: can matter in a macroscopic quantum state — a superconductor, a superfluid, a Bose–Einstein condensate — alter the gravitational field it sits in? They collect the experiments first. Podkletnov's rotating, levitating YBCO disks, above which test masses appeared to lose a few tenths of a percent of their weight. His 2002 discharge chamber, where a two-million-volt spark through a superconducting cathode produced a focused beam carrying far more momentum than its energy divided by the speed of light. Tajmar's rotating rings and gyroscopes, Chiao's attempt to convert microwaves into gravitational waves and back. Then the theory: Schiff and Barnhill's result that gravity leaves an electric field inside a conductor, a Josephson current driven by Earth's gravity alone, and Ginzburg–Landau calculations predicting a measurable local change of gravity inside a large high-temperature sample near its critical temperature.
Connection
This is the reference review for chapter 11 — the whole gravity-and-superconductors literature, experiments and theory together, gathered by three physicists who work in the field and who name exactly which results stand and which are still open. It is also chapter 2's territory: the mechanisms proposed here run through the local vacuum energy term, the zero-point energy of the lattice phonons, and a dynamical Casimir effect in gravity.
From the source
Podkletnov's 1997 experiment reported that samples of several different materials suspended above a 27-centimetre bi-layer YBCO ring, levitated and spun to 5,000 revolutions per minute below 70 kelvin under a 3.2 to 3.8 megahertz radio-frequency field, all lost the same fraction of their weight — typically 0.3 to 0.5 percent — inside a sharply bounded shielding cylinder. The authors state plainly that these results have been, until now, neither confirmed nor disproved.Section 2.1
In the 2002 experiment a Marx generator producing up to 2,000 kilovolts and peak currents of 10 kiloamperes was discharged through a two-layer YBCO cathode in a low-pressure chamber. In coincidence with the diffuse discharges above 500 kilovolts, an anomalous non-electromagnetic emission was observed, propagating in a focused beam along the chamber axis and reaching large distances without attenuation; the energy carried was of order one millijoule but the momentum was much larger than that energy divided by the speed of light, so it behaved as a short-lasting force beam.Section 2.2
Schiff and Barnhill showed that the electric field inside a conductor does not vanish when a gravitational field is present: what vanishes is the generalised field, the electric field plus the carrier mass over charge times the gravitational acceleration. The same logic applies to magnetic fields in superconductors — the Meissner effect requires the vanishing not of the magnetic field but of the magnetic field plus the mass times the gravitomagnetic potential, and it is the flux of that combination through a superconducting ring which is quantised.Section 4.1, Generalized Fields and Potentials
Ummarino and Gallerati's model predicts a Josephson effect driven by Earth's static gravity alone: the generalised potential difference across an insulating barrier of thickness one nanometre gives an alternating supercurrent of angular frequency about 1.7 by 10⁻⁴ per second, a period of about 3.7 by 10⁴ seconds, so the oscillation can only be seen in a very stable junction over an experiment lasting more than a day. The effect disappears when the junction is rotated so its surface normal is perpendicular to gravity.Section 4.2, Josephson Effect Induced By Gravity
Thin superconducting films are predicted to be highly reflective mirrors for gravitational waves at microwave frequencies. Cooper pairs, protected from decoherence by the energy gap, move non-geodesically while the lattice ions are carried along with space, and the resulting charge separation produces a virtual plasma excitation that enormously enhances the film's interaction with the wave. The same formulation predicts a dynamical gravito-phonon Casimir effect, the zero-point energy of the ionic lattice being modulated by the gravitational wave.Section 3.3, Charge Separation and Dynamical Casimir Effect; Section 4.7.4, Gravitational Waves Mirroring
Solving the time-dependent Ginzburg–Landau equations for a superconductor in Earth's static gravity, Ummarino and Gallerati predict a temporary local reduction of the gravitational field inside the sample of order 2 by 10⁻⁵ for a bismuth-strontium-calcium-copper-oxide sample near its critical temperature of about 109 kelvin — maximised by large samples, deliberate disorder, materials that are bad conductors in the normal state with low Fermi energies, and operation very close to the transition.Section 4.7.6 and 4.7.7
The way in
https://doi.org/10.3389/fphy.2022.941858How to cite it
A. Gallerati, G. Modanese, G.A. Ummarino (2022) Interaction Between Macroscopic Quantum Systems and Gravity doi:10.3389/fphy.2022.941858