Quantum detectors to be laser-healed in space

A satellite to test in-orbit laser annealing was sent into orbit from the International Space Station (ISS) today, marking an important step towards the realization of secure quantum communication using satellites and a global quantum internet.

University of Waterloo professor Thomas Jennewein from the Department of Physics and Astronomy and a member of the Institute for Quantum Computing collaborated with the University of Illinois Urbana-Champaign to design, build and test the “Cool Annealing Payload Satellite (CAPSat)” that will perform in-orbit tests and annealing of single-photon detectors based on silicon avalanche photo diodes.

The Cool Annealing Payload Satellite (CAPSat) deploying from the robotic arm of the International Space Station (ISS) to begin its in-orbit quantum annealing experiments is shown in a screenshot from the live feed. See a recording of the deployment. 

CAPSat is the first attempt at performing in-orbit laser annealing to heal damage due to constant space radiation. Laser annealing is a process of exposing the detector to a bright laser for a short period of time, which heals some of the radiation damage, and prolongs the detector’s lifetime in space. CAPSat performs this process in-orbit to repeatedly treat the detectors when they are not actively being used for quantum communication links. Previously, these tests took place in labs after being exposed to radiation at a particle accelerator thereby mimicking the expected radiation and healing in space.

The photodetector module during the final flight hardware test in the Quantum Photonics Lab at the Institute for Quantum Computing.

Exposure to space radiation damages the ultra-sensitive photodetectors that are onboard quantum communication satellites, making the photodetectors less reliable over time at detecting single photons. This prevents the satellites from performing Quantum Key Distribution (QKD), which guarantees a secure communication channel even against an attack from a hacker. CAPSat aims to study novel approaches to anneal the photodetectors and maintain the satellite’s ability to perform secure QKD without the need for excessive cooling.

One of the biggest challenges was designing the satellite components to fit in the tight dimensions – a mere 10 cm square by 30 cm long, and to operate with low power consumption. IQC research associate Nigar Sultana, who has been working on the detector module for the CAPSat project since it kicked off six years ago, said “everything matters, even the small things like glue.” Although small in size, CAPSat’s potential impact is big; it could provide a very efficient method to mitigate radiation damage of single-photon detectors in orbit.

Canadian principal investigator Thomas Jennewein and Research Associate Nigar Sultana meet with Paul Kwiat and collaborators at the University of Illinois at Urbana-Champaign.

“The deployment of CAPSat demonstrates proof of concept that will pave the way for future quantum communication missions,” said Jennewein.

CAPSat was successfully launched into space on Sunday, August 29 on board the SpaceX Dragon CRS-23 cargo ship, arriving at the ISS. Today at 7:00 EDT, it was deployed in its transport canister from the ISS robotic arm and begins in-orbit quantum annealing experiments. See a recording of CAPSat's launch.

The Waterloo team acknowledges dedicated support by the Canadian Space Agency (FAST program).