Re-thinking plans in the times of COVID-19

My project aims to investigate the dynamics of a particular class of phase transitions happening in the quantum realm.

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More specifically, I am looking at open quantum systems (i.e., systems which interact with an external quantum system, usually called environment or bath). They can undergo interesting phenomena called dissipative quantum phase transitions (i.e., phase transitions triggered by a non-thermal parameter, where energy and/or information flows from the system to the environment irreversibly). Another defining feature of these systems is that they retain memory (i.e., there can be non-immediate feedback effects from the environment to the system; in technical jargon, they are non-Markovian). The Python algorithm I have been working on last summer - which should have been the focus of this year's project as well - computes the dynamics of open quantum systems and explores their behaviour under the variation of different parameters. 

One of the graphs that I produced last year. When the parameter alpha is varied, the behaviour of the system changes from underdamped oscillation to localisation. This change of behaviour effectively constitutes a dissipative quantum phase transition.

I am not going to delve further into the details of how the algorithm works, all you need to know is that it requires a good amount of computational power to be run. Something which, unfortunately, my personal computer lacks. Last year this was not an issue, as the physics department equipped me with a machine that met all the necessary criteria for my coding work. This year, however, with the university closed due to the pandemic, I found myself lacking the very essential resource I need for my research. Long story short, I had to re-consider my aims and think carefully about how to make the most out of the second part of my Laidlaw project. After having discussed with my supervisor, we concluded that it would be best to split it into two parts. The first two weeks, at the beginning of summer, were to be done remotely, while the remaining three weeks in St Andrews. This is subjected to when the university resources become again available, either - hopefully - at the end of summer, or during Christmas break. At the moment, I have almost finished the first research block. Sadly unable to code, I have spent this time focusing on relevant papers. I deepened my understanding of dissipative quantum phase transitions by looking at the underlying theory, specifically focusing on the the localisation transition in the sub-ohmic spin-boson model. I am currently writing a short review on the state-of-the-art of the field. The second block will (finally!) involve getting my hands back on coding and improving on my work of last year.

I would like to thank my supervisor, Dr Brendon Lovett, for the opportunity of researching this incredibly interesting quantum phenomena, the Capod team, and Lord Laidlaw, who made the Laidlaw Scholarship program possible.

Riccardo Bonzano

MPhys Theoretical Physics student, University of St Andrews

Last year Theoretical Physics Master's student at the University of St Andrews. My Laidlaw project involved investigating the physics of open quantum systems. I am interested in how technology can aid our transition to a more ethical and sustainable society.

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