Simultaneous measurement of group and phase delay between two photons - art. no. 063808

We report on an experiment to determine both the group and phase delays exp erienced by orthogonally polarized photon pairs traveling through a birefri ngent medium. Both types of delay are determined from the same set of coinc idence-counting data. The experiment is based on an interference technique using two-photon multipath indistinguishability to produce an interference feature. Earlier work has shown that this interference feature can be used to measure the group velocity of single-photon wave packets in dielectric m edia. In the current: work, the two-photon interferometer has been modified to produce an additional interference feature that is sensitive to the pha se velocity of the light. We have used this technique to simultaneously mea sure the group delay in crystal quartz with a precision of 0.1 fs and the p hase delay with a precision of 8 attoseconds. Our analysis clarifies the ef fects of group and phase delays and shows the unexpected result that disper sive temporal broadening, which is well known to be canceled for the origin al interferometer setup, is not canceled for this type of ''postponed compe nsation'' interferometer.