Towards calorimetric detection of individual itinerant microwave photons

Joonas Govenius

Research output: ThesisDoctoral ThesisCollection of Articles


This dissertation focuses on the development of a new type of thermal microwave photodetector based on superconductor–normal-metal–superconductor (SNS) junctions. We motivate the development of the detector mainly by microwave quantum optics applications in the context of superconducting qubits coupled to microwave transmission lines and resonators, i.e., in the context of circuit quantum electrodynamics (cQED). In cQED, single-photon microwave pulses naturally arise as a results of a qubit exchanging its excitation with a transmission line. While immense progress has been achieved in cQED in general, and in linear microwave amplification in particular, the challenge of developing an efficient and practical detector for single itinerant photons remains open, mostly due to the exceedingly small energy of individual microwave photons. This prevents microwave implementations of a certain class of quantum optical protocols, including the parity measurement protocol proposed in this dissertation. The core of this dissertation is dedicated to introducing our detector design, discussing the thermal properties of the detector in detail, and demonstrating the operation of the detector in a time-gated threshold detection mode. In particular, we demonstrate threshold detection of coherent 8.4 GHz microwave pulses containing roughly 200 photons, or 1.1 zJ of energy. Compared to other thermal detectors, this is an order of magnitude improvement in the energy of the detected pulses. In addition, we characterize the linear response of the SNS junctions as separate components. That is, we embed the junctions in a microwave circuit that is specifically designed to allow determining the electrical admittance of the SNS junctions from the response of the circuit as a whole.
Translated title of the contributionKohti yksittäisten vapaiden mikroaaltofotonien kalorimetristä mittausta
Original languageEnglish
QualificationDoctor's degree
Awarding Institution
  • Aalto University
  • Kaivola, Matti, Supervising Professor
  • Möttönen, Mikko, Thesis Advisor
Print ISBNs978-952-60-7002-5
Electronic ISBNs978-952-60-7001-8
Publication statusPublished - 2016
MoE publication typeG5 Doctoral dissertation (article)


  • microwave
  • photodetection
  • calorimetric
  • SNS


Dive into the research topics of 'Towards calorimetric detection of individual itinerant microwave photons'. Together they form a unique fingerprint.

Cite this