Letian Yu, Year 4, Physics and Applied Physics |
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What’s your project about – in a nutshell?
We usually think of mass as something inherent to objects—from massive stars to tiny particles like electrons—and that energy is always conserved. For example, an electron moving through an electric field may gain or lose energy, but the total energy remains constant.
In this project, we explored what happens when that rule is broken. Specifically, we studied how special particles called Dirac quasiparticles behave in systems where energy can be added or removed without balancing out—also known as gain and loss. It’s a deep dive into what happens when one of physics’ most fundamental assumptions no longer holds.
What sparked the idea for this project?
In physics, there’s often a gap between idealised systems—where nothing is gained or lost—and real-world systems, which are open and constantly interacting with their environment. That gap sparked our curiosity. We wanted to know: under what conditions can a messy, non-conserving system start behaving like a perfect, closed one? This project was about uncovering those special conditions.
How did your project evolve from idea to outcome?
The project began with theoretical explorations by my senior, Haoran, who questioned what would happen in non-conserving systems. To test these ideas experimentally, we needed a physical setup that could mimic energy exchange with the environment. After some exploration, we found that optical fibers were the ideal platform—allowing us to precisely control gain and loss while studying how light, and thus the system, behaves.
What was a tough or challenging moment, and how did you work through it?
One major challenge was how incredibly sensitive the setup was. Even a slight tap on the table—without touching the fiber—could throw the signal off completely. The real culprit turned out to be changes in the light’s polarization. These tiny shifts disrupted everything. After a lot of trial and error, we tuned each section of the setup to maintain stable polarization. Once we solved that, the experiment started to produce usable results.
What was the most fun or satisfying part of the project?
At the start, I had very little experience with optical experiments. Learning to use the equipment and build the setup was a steep learning curve. But thanks to support from my seniors and colleagues, the project gradually came together. It was really rewarding to watch the system finally work after overcoming all the early difficulties.
One thing you learned – about the topic, or yourself?
I used to think of gain and loss as tools in basic optical devices—things like amplifiers or filters. But through this project, I learned they can fundamentally alter particle-like properties, even something as intrinsic as mass. That idea blew my mind. It made me realise that many physical properties we take for granted might be more controllable than we think.
Any advice for students?
Never underestimate the importance of reading journal articles. It’s not just about staying updated—it helps you build intuition and gives you the vocabulary to discuss your work clearly. Even when the terminology seems overwhelming at first, reading widely will help everything click into place.