  We study the excitation of a one-electron quantum cyclotron by gravitational
waves. The electron in such as a penning trap is prepared to be at the lowest
Landau level, which has an infinite degeneracy parameterized by the size of the
wave function. We find that the excitation rate from the ground state to the
first excited state is enhanced by the size of the electron wave function: an
electron with a larger wave function feels gravitational waves more. As a
consequence, we derive a good sensitivity to gravitational waves at a
macroscopic one-electron quantum cyclotron.
