Abstract

In parametric downconversion, pump photons are converted into pairs of signal and idler photons. A photodetector counting photons in the idler beam can be used to gate a homodyne detector in the signal beam so that it is on only when an n-photon wave packet enters its input. The probability distribution for the charge delivered by the homodyne detector has the same form as the position probability distribution of a harmonic oscillator in its nth energy eigenstate. In particular, the probability distribution exhibits fringes. We have calculated the visibility of these fringes for the case when both the photodetector and the homodyne detector have less than unit quantum efficiency. By reducing the photon flux in the signal and idler beam sufficiently, the effect of idler photodetector loss on the fringe visibility can be made negligible. The degree to which the fringes have been degraded then depends only on the inefficiency of the homodyne detector. For the case n = 1, the fringe is still visible when the homodyne detector efficiency is 0.5. Hence the proposed experiment should be feasible with existing technology.

© 1987 Optical Society of America