  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 the nonlocality implied by the superposition
principle, and the locality implied by the equivalence principle. Experimental
consequences of this conceptual tension will be explored for macroscopically
coherent quantum fluids, such as superconductors, superfluids, and atomic
Bose-Einstein condensates (BECs), subjected to tidal and Lense-Thirring fields
arising from gravitational radiation. A Meissner-like effect is predicted, in
which the Lense-Thirring field is expelled from the bulk of a quantum fluid.
Superconductors are predicted to be 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 beneath
the surface of the superconductor. A simple, Hertz-like experiment has been
performed to test these ideas, and preliminary results will be reported.
