Abstract
Single-photon detection is an essential component in many experiments in quantum optics, but it remains challenging in the microwave domain. We realize a quantum nondemolition 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 a single shot, we reach an external (internal) photon-detection fidelity of 50% (71%), limited by transmission efficiency between the source and the detector (75%) and 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 nondemolition nature. We envisage applications in generating heralded remote entanglement between qubits and for realizing logic gates between propagating microwave photons.
3 More- Received 5 December 2017
- Revised 25 February 2018
DOI:https://doi.org/10.1103/PhysRevX.8.021003
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Viewpoint
Single Microwave Photons Spotted on the Rebound
Published 23 April 2018
A cavity-confined qubit can register the reflection of a single microwave photon without destroying it.
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Popular Summary
Modern information technology uses electromagnetic fields to encode and transmit information. Similarly, single photons—the elementary particles of such fields—are important carriers of quantum information. The detection of individual photons is well established at the near-infrared wavelengths used in telecom devices. However, detection of microwave photons—essential for certain approaches to quantum computing—remains challenging because of the much lower photon energy. Earlier schemes for microwave photon detection have often been limited by long dead times after a detection, low efficiency due to mode mismatches, or the requirement to trap the photons in a long-lived cavity mode. Here, we experimentally demonstrate a novel method for detecting single microwave photons with high fidelity.
Our setup consists of a source of single photons connected to our detector—a superconducting artificial atom coupled to two quarter-wave coplanar waveguide resonators acting as single-mode cavities. Our photon detection fidelity is 50%, a metric that accounts for both missed photons and false positives. In contrast to previous designs, the detected photon continues its propagation without being absorbed by the detector. To achieve this performance, we use a control sequence that entangles the incoming photon with the state of the superconducting atom, as well as single-shot qubit readout to detect the presence of the photon.
This detector design could find applications in remote-entanglement protocols as well as in linear optics quantum computation in the microwave regime.