Sarah Croke was a postdoctoral researcher and PSI fellow at Perimeter Institute for Theoretical Physics. Now she is a Professor of Theoretical Physics at the University of Glasgow, analyzing gravitational waves with quantum computers.
Perimeter Institute alumni have gone on to a wide variety of roles after leaving the Institute. As an undergraduate, Sarah Croke was focused on understanding the formalism of quantum mechanics; since then her focus has shifted to how quantum mechanics can be used to analyze computationally intensive gravitational wave data from LIGO. We reached out to Sarah to learn more about her journey.
This interview has been lightly edited for clarity and length.
What is your current role, and how are you trying to push boundaries in your field?
I am a Professor of Theoretical Physics at the University of Glasgow, and Convenor of Learning and Teaching for the School of Physics and Astronomy. I lead a small team, currently three postdoctoral researchers and three PhD students. Our primary focus is exploring quantum algorithms for gravitational wave data analysis, a collaboration with gravitational wave physicists.
In the decade since the historic first direct detection of gravitational waves, LIGO has detected dozens of compact binary coalescence events, in which two massive, dense orbiting objects merge, emitting gravitational radiation. Nonetheless, data analysis tasks are extremely computationally intensive, and new techniques are needed to identify and categorize candidate signals. Other classes of sources, notably continuous waves, are also expected but have not yet been detected, in part due to the computational difficulty caused by the sheer number of possible template signals which must be compared against data to look for a good match.
We are seeking to push the boundaries of what is possible, both in principle, on an as yet hypothetical fault-tolerant quantum computer, and in practice, on near-term noisy quantum devices, or through quantum-inspired algorithms, to allow faster analysis, and even, in the best case, detection of new classes of signals.
What brought you to where you are now?
I think I just kept following what was interesting to me. I wasn’t someone who was always going to be a scientist, I just found I was good at mathematics and science, and there was always more to learn. As an undergraduate I can still remember quantum mechanics being completely unfathomable to me, so I had to spend time trying to understand the formalism, and develop intuition. I enjoyed the challenge of trying to get to the bottom of it. To some extent I’m still trying, but now my focus has shifted to understanding what is made possible by quantum mechanics.
There’s a book by Richard Feynman, The Pleasure of Finding Things Out, and I think that phrase sums up the joy of doing research. There’s a moment in any research problem where you learn something new, and even if it’s just something small, there’s a brief moment where you’re the only person in the billions of people on Earth who knows that particular thing. That feeling is what carried me to where I am now.
You need quite a bit of resilience of course, and I’ve had a lot of support along the way, from mentors, collaborators, and friends.
What are you passionate about?
These days I like a quiet life! I like spending time with my family, we bake a lot. I like to draw when I have time, and mostly I like to curl up with a good book. My favourite is To Kill A Mockingbird, and I’ve recently finished the Three-Body Problem trilogy.
How has your work impacted your industry and community?
Research on the limits of communication dating from the 1960s established criteria for constructing optimal measurements to discriminate between different possible signals encoded in quantum states. My PhD research introduced a new strategy, which has since become a standard reference in the field, finding applications in a range of quantum information protocols e.g. bit commitment, coin flipping, teleportation.
At Perimeter Institute, I had the opportunity to collaborate with faculty member Daniel Gottesman on a proposal to use techniques developed in quantum information to improve the resolution of astronomical imaging. This broadened the potential impact of quantum technologies to astronomy, and put forward new requirements on the development of quantum repeaters, thus guiding the development of this fledgling technology. This has become a seminal work, starting a new field of quantum-enhanced astronomy.
My recent work was the first to introduce gravitational wave data analysis as an application area for quantum computers. We gave a comprehensive analysis of the resource requirements to address practically relevant problems in gravitational wave data analysis, and of the technical requirements to enable searches which remain infeasible with current techniques. This has been followed up by other groups, and a new field is now developing around this work.
How do you give back to your community?
In 2021 I established a mentoring scheme at the University of Glasgow pairing undergraduate students from under-represented groups with industry mentors. Together with colleagues I set up this scheme from scratch, adapting training resources, arranging events, and recruiting and matching students and mentors. The scheme is now managed by the College Employability team, but I am still involved in matching students to mentors. 82 pairs have been matched since the programme began.
In 2018 I established the Quantum Technology School (QTS), a two day event for high school students at the University of Glasgow. This was partly inspired by my experience contributing to programmes at Perimeter Institute and the University of Waterloo’s Institute for Quantum Computing, such as Perimeter’s International Summer School for Young Physicists. The QTS emphasizes hands-on activities, and information about further study, as well as keynote lectures to enthuse young people about quantum technology. It features a diverse range of speakers and workshop leads in terms of gender, ethnicity, and career stage as role models. We made a deliberate choice to aim to attract as broad an audience as possible, to encourage pupils who may not already be thinking about a career in science to consider further study. Over the years we have welcomed over 700 pupils to these events.