, e . g . , superconducting transducers between electromagnetic and gravitational radiation ?

One of the conceptual tensions between quantum mechanics (QM) and general relativity (GR) arises from the clash between the spatial nonseparability of entangled states in QM, and the complete spatial separability of all physical systems in GR, i.e., between nonlocality implied by the superposition principle, and locality implied by the equivalence principle. Experimental consequences of this conceptual tension for macroscopically coherent quantum objects, such as superconductors, superfluids, and atomic Bose-Einstein condensates, subjected to tidal and LenseThirring fields arising from gravitational radiation, will be explored. In particular, superconductors will be considered as macroscopic quantum gravitational antennas and transducers, which can directly convert upon reflection a beam of quadrupolar electromagnetic radiation into gravitational radiation, and vice versa, and thus serve as both sources and receivers of gravitational waves. An estimate of the transducer conversion efficiency on the order of unity comes out of the Ginzburg-Landau theory for an extreme type II, dissipationless superconductor with minimal coupling to weak gravitational and electromagnetic radiation fields, whose frequency is smaller than the BCS gap frequency, thus satisfying the quantum adiabatic theorem. The concept of “the impedance of free space for gravitational plane waves” is introduced, and leads to a natural impedance-matching process, in which the two kinds of radiation fields are impedance-matched to each other around a hundred coherence lengths