  An electromagnetic field quadrature measurement, performed on one of the
modes of the nonlocal single-photon state $a|1,0>-b|0,1>$, collapses it into a
superposition of the single-photon and vacuum states in the other mode. We use
this effect to implement remote preparation of arbitrary single-mode photonic
qubits conditioned on observation of a preselected quadrature value. The
quantum efficiency of the prepared qubit can be higher than that of the initial
single photon.
