The superconducting gravity bench — an emitter and a mirror

Why the library suggests it

Gary Stephenson's design joins a plain s-wave superconductor such as lead to a d-wave cuprate such as YBCO, so that a pair crossing between the two symmetries must change its orbital angular momentum by two units — and a spin-two transition is the one that emits a graviton. One graviton is hopelessly rare, but coherent emitters add as the square of their number, so a wafer full of them is a different proposition; the paper draws the wafer, with thin films, a 24 gigahertz phased array, and a power and sensitivity budget for a first test (Stimulated Emission of Gravitational Waves via Dissimilar Superconducting Josephson Junctions, 2026). The mirror argument is Raymond Chiao's, with Stephen Minter and Kirk Wegter-McNelly: the Cooper pairs carrying a supercurrent are smeared across the whole film by the uncertainty principle and protected by the energy gap, so they cannot ride along with a passing wave while the lattice ions do; charge separates, an enormous Coulomb force answers, and the film stiffens against the wave by the ratio of the electric to the gravitational force between two electrons — forty-two orders of magnitude (Do Mirrors for Gravitational Waves Exist?, 2009, with the short checkable version at Laboratory-Scale Superconducting Mirrors for Gravitational Microwaves, 2009). The full theoretical machine — London equations, Meissner effect and penetration depth rewritten for gravity — is Interaction of gravitational waves with superconductors (2016), and the price of a positive result is stated plainly by a reviewer: the coupling would have to be roughly twenty orders of magnitude stronger than Newtonian gravity (The Chiao Gravity-Superconductor EM Transducer, 2012).

The experiment or build

Fabricate the junction array and the film in the same clean room and put them face to face in one cryostat, so the emitter and the detector are the same experiment. Drive the array at its design bias and frequency; look for a response in the film that scales as the square of the number of driven junctions, which is the coherence signature and the thing ordinary crosstalk cannot fake. The settling measurement is received signal against the number of coherently driven emitters, with a square-law fit, and with the whole curve collapsing when the array is driven incoherently at the same total power. Radiated power scales as the fourth power of frequency and strain as the square, so the design frequency is the other lever worth sweeping.