Abstract

The purpose of an interaction-free measurement is to detect the presence of an object without letting any energy quanta be absorbed by the object. In 1993, Elitzur and Vaidman¹ proposed a scheme where the presence of an object could be detected with a 25% probability, without the object absorbing any photons. In that scheme, the absence of the object was detected with total certainty. The commonly established figure of merit for such a measurement η_EV is, assuming that there is an absorbent in the setup, the probability for a successful interaction-free measurement divided by the total probability of detecting the absorbent. Recently, several schemes have been pro-posed²⁻⁵ that have a higher η_EV than in Elitzur and Vaidman’s original proposal. In this work we present interaction-free measurement results using a Fabry-Perot interferometer (FPI) as a measurement apparatus. If the cavity of the interferometer is empty, an incoming photon will be transmitted through the interferometer. If an absorbent is placed between the mirrors, the photon will be reflected by the first mirror. By detecting which way the photon takes, we will gain information about the presence of the absorbent without losses/interaction. For a perfect measurement, η_EV will be equal to the mirror reflectivity R. Thus, in theory, one can approach the perfect interaction-free measurement simply by increasing R.

© 1998 Optical Society of America