Single-Shot Quantum Non-Demolition Detection of Individual Itinerant Microwave Photons

Jean-Claude Besse, Simone Gasparinetti, Michele C. Collodo, Theo Walter, Philipp Kurpiers, Marek Pechal, Christopher Eichler, and Andreas Wallraff
Laboratorium fur Festkörperphysik, ETH Zurich, Switzerland

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 individual itinerant microwave photons [1], and characterize its performance using a single-photon source. By using a cavity-assisted conditional phase flip gate between a photon and a superconducting artificial atom, the information of the presence of an itinerant photon is mapped into a definite state of the qubit. By reading out the state of this atom in single shot, we reach an external photon detection fidelity of 50%, limited by transmission efficiency between the source and the detector (75%) and the coherence properties of the qubit. We demonstrate the quantum non-demolition nature of the detector by characterizing the field of the reflected photon, which is never absorbed. We envisage applications in generating heralded remote entanglement between qubits and for realizing logic gates between propagating microwave photons.
[1] Besse et al., PRX 8, 021003 (2018)