  We extend Einstein's hole argument into the quantum domain, and argue that
quantum observables for quasiclassical superpositional states of gravitational
fields require additional information to be well-defined, namely, relative
positions of the gravitational fields involved in superpositional states. As a
consequence, for the definition of these quantum observables we need a common
background. The observable is a transition probability in a simple double-slit
experiment with partial gravitational measurement of position. It may be easily
computed in non-relativistic Schroedinger theory with Newtonian potential.
