  We show that controlled interference of a particle's wavefunction can be used
to perform a quantum mechanical measurement in an incomplete basis. This
happens because the measurement projects the particle into a lower dimensional
subspace of the Hilbert space of the incoming wave. It allows a sender (Alice)
to signal the receiver (Bob) nonlocally, by Alice's choosing to measure in a
complete or incomplete basis (in general: bases of differing incompleteness).
If experimentally confirmed, it furnishes a new quantum communication act:
nonlocal transmission of a bit without concomitant causal communication.
However, the question of its compatibility with special relativity remains
unresolved.
