  Pairs of Planck-mass--scale drops of superfluid helium coated by electrons
(i.e., "Millikan oil drops"), when levitated in the presence of strong magnetic
fields and at low temperatures, can be efficient quantum transducers between
electromagnetic (EM) and gravitational (GR) radiation. A Hertz-like experiment,
in which EM waves are converted at the source into GR waves, and then
back-converted at the receiver from GR waves back into EM waves, should be
practical to perform. This would open up observations of the gravity-wave
analog of the CMB from the extremely early Big Bang, and also communications
directly through the interior of the Earth.
