According to classical physics, electromagnetic waves do not interact with each in the vacuum of empty space. However, the more fundamental description of reality — quantum field theory — predicts that light-by-light interactions can occur due to quantum fluctuations of matter, which endow the vacuum with nonlinear properties similar to a dielectric medium. While this effect was predicted almost 100 years ago, it has yet to be experimentally observed due to its incredibly small magnitude. Additionally, light-by-light scattering could contain contributions from undiscovered particles, which could be used to design new kinds of particle detectors looking for dark matter candidates (such as axions) or other exotic particles. In principle, light-by-light scattering could even shed light on one of the most pressing problems in theoretical physics: the quantum nature of gravitation and spacetime [1].

This theoretical physics will explore how light-by-light interactions can be detected by adapting established quantum sensing technologies, particularly laser interferometers enhanced by the use of optical cavities. Broadly, this project has two goals:
1. To design precision measurement methods that would allow signatures of light-by-light scattering to be detected with current laser technologies;
2. To explore how experiments looking for light-by-light interactions can be used to constrain the properties of postulated particles beyond the Standard Model of particle physics, such as axions and gravitons.

The work will involve analytic and semi-analytical calculations using techniques from quantum field theory, quantum information theory, and quantum optics. Projects may also involve numerical simulations.

[1] Mehdi, Hope, & Haine, PRL 130 (24), 240203 (2023)

• Many-body quantum mechanics (e.g. as covered in PHYS3101)
• A background in quantum field theory or quantum optics would be useful, but not necessary