PhD candidate Kyle Thompson receives the 2026 Xanadu Award for an Outstanding Publication

Through generous support from Xanadu, the Xanadu Award for an Outstanding Publication was established in the Department of Physics to acknowledge PhD students who have published a peer-reviewed article in an academic journal on a topic related to quantum information and quantum optics. We are delighted to announce this year's recipient Kyle Thompson – who received the award in recognition of his paper "How much time does a photon spend as an atomic excitation before being transmitted through a cloud of atoms?”, which was published in APL Quantum Journal in 2025.

This award is the result of a donation from Xanadu, a Toronto-based start-up company with close ties to the Department of Physics. A number of former post-doctoral fellows, PhD students and undergraduate students are affiliated with Xanadu.

Xanadu founder and CEO Christian Weedbrook says “we wanted to encourage students in the field of quantum information and quantum optics and to let them know that Xanadu, and many other quantum startups in Canada, exist when they graduate.”https://pubs.aip.org/aip/apq/article/2/3/036108/3364127/How-much-time-does-a-photon-spend-as-an-atomic

Kyle Thompson shared his thoughts on his award-winning research:

In this paper we answer a very simple yet fundamental question about light-matter interaction: if a photon passes through a cloud of atoms without being scattered, does it spend any time as an atomic excitation along the way? If so, how much? We introduce a way of defining and measuring this time by monitoring the atoms with a second beam of light. Surprisingly, we show that this time can be negative because of quantum interference. These results provide a new perspective on how light propagates through an absorbing medium—a process that is central to atomic, molecular, and optical physics and plays an important role in many emerging quantum technologies.

What theoretical framework or experimental setup did you use, and what made it particularly effective for your study?

This problem is theoretically challenging for two reasons. First, we wanted to know not just the average time a photon spends as an atomic excitation, but the time conditioned on the photon successfully passing through the cloud. Second, the full quantum description of a photon propagating through a cloud of atoms is very complicated because the photon can scatter into an effectively infinite number of directions.

To address these challenges, we combined two theoretical tools that are not often used together: the weak value formalism and quantum trajectory theory. This combination was especially effective because it allowed us to isolate the single quantum trajectory in which the photon is transmitted through the cloud, without having to explicitly describe all of the many ways it could have instead been scattered.

How could your findings influence future developments in physics or related technologies?

This work is the result of purely curiosity-driven research. We asked a conceptually simple question about light-matter interaction, and we were genuinely surprised by the answer. Although the paper is fundamentally about deepening our understanding of a basic physical process, such advances in perspective can often shape how researchers think about related problems. By offering a new perspective on light-matter interaction, this work may help inspire further developments in quantum optics or related technologies. More broadly, I hope that our findings serve as a reminder that curiosity-driven research can lead to unexpected and meaningful insights.