Nondestructive quantum measurements are central for quantum physics applications ranging from quantum sensing to quantum computing and quantum communication. Employing the toolbox of cavity quantum electrodynamics, we here concatenate two identical nondestructive photon detectors to repeatedly detect and track a single photon propagating through a 60m long optical fiber. By demonstrating that the combined signal-to-noise ratio of the two detectors surpasses each single one by about two orders of magnitude, we experimentally verify a key practical benefit of cascaded non-demolition detectors compared to conventional absorbing devices.
@article{arxiv.2105.14354,
title = {Detecting an Itinerant Optical Photon Twice without Destroying It},
author = {Emanuele Distante and Severin Daiss and Stefan Langenfeld and Lukas Hartung and Philip Thomas and Olivier Morin and Gerhard Rempe and Stephan Welte},
journal= {arXiv preprint arXiv:2105.14354},
year = {2021}
}