Single-photon detection is an essential component in many experiments in quantum optics, but remains challenging in the microwave domain. We realize a quantum non-demolition detector for propagating microwave photons and characterize its performance using a single-photon source. To this aim we implement a cavity-assisted conditional phase gate between the incoming photon and a superconducting artificial atom. By reading out the state of this atom in single shot, we reach an internal photon detection fidelity of 71%, limited by the coherence properties of the qubit. By characterizing the coherence and average number of photons in the field reflected off the detector, we demonstrate its quantum non-demolition nature. We envisage applications in generating heralded remote entanglement between qubits and for realizing logic gates between propagating microwave photons.
@article{arxiv.1711.11569,
title = {Single-Shot Quantum Non-Demolition Detection of Itinerant Microwave Photons},
author = {Jean-Claude Besse and Simone Gasparinetti and Michele C. Collodo and Theo Walter and Philipp Kurpiers and Marek Pechal and Christopher Eichler and Andreas Wallraff},
journal= {arXiv preprint arXiv:1711.11569},
year = {2018}
}