UCL Quantum Science and Technology Institute


Alumni Matters: Dr Johnnie Gray

1 October 2020

Catching-up with alumni of the EPSRC Centre for Doctoral Training in Delivering Quantum Technologies.

Photo of Johnnie Gray


CDT COHORT 1: 2014-18

Theoretical Scientist in the Division of Chemistry and Chemical Engineering at Caltech

Research interest: Quantum Information/Tensor Networks

Q. How did the CDT environment benefit you?

Doing a PhD in a cohort with lots of structure is a very good way to do a PhD. It means you are not stuck alone in a library for 6 months trying to work out what to do like many other conventional programmes. Also, the quality of the guest lectures during my time at UCL was really very high - we heard about lots of things we wouldn’t have heard about otherwise.

Q. What was the focus of your PhD?

I explored many-body entanglement in classical & quantum simulators. The intersection between many-body problems and entanglement in quantum systems is a really interesting topic that spans many different fields. For example, we know lots about the basic rules of quantum mechanics, but we still don’t know how many things in the world around us emerge from the complex interaction of these rules, and that is an intriguing mystery.

Q. What happened next?

Based on my previous research work on tensor networks, I was asked to come work with a group at Caltech.  Here we do a mix of quantum computation and simulation. We hope to simulate quantum systems and look at applications in quantum chemistry. At the moment detailed quantum simulations for chemistry are a long way away into future. So, one question is what might we be able to do that is useful soon, that isn’t directly replicating what we can already do classically. 

After completing his PhD at UCL, Dr Johnnie Gray was a Research Associate at Imperial College London before moving to the California Institute of Technology, USA.

This article was featured in UCLQ’s 2019/20 annual report.