Watching a photon interfere with itself

摘要

We observe the self-interference of a photon at femtosecond timescales. The photon is one member of an entangled photon pair and, after passing through a Michelson interferometer, it is reunited with the second pair member in a nonlinear crystal. There the pair may recombine into a single photon; the probability of recombination as a function of the arrival time of the second photon reveals the self-interference of the Michelson photon, with bandwidth-limited temporal widths (approximate to 20 fsec) and with sub-femtosecond instrumental resolution. To support the observations, the pair recombination amplitude is determined from first-order perturbation theory in the interaction picture, which leads to good comparisons with the experimental results. It is demonstrated that our approach measures the arrival time of a photon with resolution orders of magnitude better than existing single-photon detectors.