Elliot Lloyd - Theoretical Physics Project Prize

Permutation Symmetric Quantum Trajectories, A Quantum Jump Approach for Permutationally-Invariant Processes in Open Multiqudit Systems.

Also awarded the Brewster Prize, and medal for level 5 Theoretical Physics

Elliot's project found a radically more efficient way to simulate the dynamics of models of N identical emitters coupled to a common cavity mode.  Such models arise in several different contexts—for example describing lasing, superradiant dynamics, and superradiant phase transitions.   The key idea is that models with equivalent emitters have a permutation symmetry under swapping the emitters.  However, for an open quantum system, this symmetry is what is known as a "weak" symmetry; a symmetry that exists for the ensemble averaged state, but not necessarily for the quantum state in a given experiment.  Elliot however showed that there are ways of representing this problem so that each simulated experimental "trajectory" effectively has permutation symmetry.  This has transformed what is possible for simulating such models.  For two-level emitters, exact calculations were previously restricted to ~50 emitters, but now possible for tens of thousands.  For more complex emitters with three levels, where previous work was restricted to fewer than 10, hundreds of emitters are now possible.

The results of Elliot's project are now available as a preprint, https://arxiv.org/abs/2605.11103 and an open-source library implementing this is available at https://github.com/ellxor/pimcs

 

Lara McCallion-Gow - Physics MPhys Project Prize

Lara McCallion-Gow was awarded the best final year MPhys Physics project. Her project was titled: Thermal Cycling of Perovskite Solar Cells in the Space Environment

Supervisor: Dr Lethy Krishnan Jagadamma

This project focused on investigating the thermal-cycling stability of carbon-electrode-based halide perovskite solar cells for space applications in low Earth orbit (LEO). Halide perovskites are an emerging family of highly promising photovoltaic materials, with a certified power conversion efficiency of ~ 27% demonstrated under terrestrial conditions. These materials have also shown excellent radiation tolerance, making them a key focus for research into their suitability for 'space-grade' applications.

While the radiation tolerance of halide perovskites has been extensively studied, their behaviour under thermal cycling, particularly relevant to the extreme temperature fluctuations (~±150 °C) in LEO, remains poorly understood. Gaining insights into their thermal stability under these conditions is crucial for evaluating their potential in space-grade solar panels.

In addition to thermal cycling stability, Lara’s project examined the impact of top electrode selection- a printable carbon electrode and a thermally evaporated gold electrode for the LEO region. The study found that a carbon electrode with P3HT as the hole-transporting layer is the winner among the four different device architectures explored under this investigation. This combination revealed less degradation and good thermal stability and performance retention even after multiple thermal cycles at accelerated heating/cooling cycles. In contrast, the gold electrode-based perovskite solar cells degraded rapidly under the LEO thermal stressing conditions but showed some self-recovery features after storing in the dark for 48 hours.   This study highlighted the importance of electrode/hole transporting layer combination in achieving long-term thermal stability in the LEO region.

We are currently preparing these findings for formal publication with Lara as the lead author. We warmly congratulate Lara on this significant achievement.

 

 

Callum Fettes - Physics BSc Project Prize

Modern Improvements to the DEER Experiment

Supervisors: Janet Lovett and Hassane El Mkami

Callums’s BSc project was to explore the use of shaped pulses for the EPR spectroscopy experiment of double electron-electron resonance (DEER). The experiment measures the dipolar coupling between pairs of paramagnetic centres, enabling the determination of nanometre distances. Such measurements are important for gaining deeper insights into the conformational and structural properties of soft matter, including biomolecules.

 

The EPR spectrometer in Physics has been upgraded to allow the use of pulse shaping and we are learning how to best utilise this technology. The literature is of course one way to do this, but we have found that optimisation of the methodologies on our own spectrometer requires our own research. Callum contributed valuably to this through a systematic study of the requirements of the adiabatic pulses, finding that (surprisingly) bandwidth compensation seems to be less useful than amplitude optimisation. The latter was not an effect we had previously considered. Callum worked hard on learning many different aspects required for the study and writing the work up clearly. He gave an outstanding oral presentation of the study. Callum and this project have been nominated by the School for the Inaugural Malcolm Dunn Memorial Prize. 

 

 

 

Lucy Kappai - Astrophysics MPhys Project Prize

Timescape vs Dark Energy, Investigating Dynamical Dark Energy and Inohomgeneous Cosmologies

Supervisors: Keith Horne and Rita Tojeiro

Lucy Kappai investigated the Timescape cosmology model as an alternative to standard cosmological models that require Dark Energy to drive an accelerated expansion at late times.

Dark Energy (DE) is one of the deepest mysteries and challenges to our understanding of gravity.

When Einstein formulated General Relativity (GR) to desribe gravity is a consequence of curved space-time, he introduced DE in the form of a cosmological constant $\Lambda$ so that its repulsive effect could balance the gravitational  attraction to maintain a steady -tate Universe in perfect balance.

He later regretted introducing that new term after Hubble discovered evidence for an expanding Universe.

Cosmologists resurrected DE in 1998 when observations of the peak brightness of distant supernova explosions provided convincing evidence that the expanding Universe is accelerating, rather than decelerating.

Theoretical physicists now use quantum field theory (QFT) to describe how matter behaves as waves.

The zero-point energy of fluctuating quantum fields produces a vacuum energy density that is too large by 60 or 100 orders of magnitude compared with the observed DE density, a spectacular failure that highlights our current lack of understanding.

 

Timescape is based on GR, but models an inhomogeneous two-phase Universe with a empty voids, as we observe in the present-day distribution of galaxies.

GR predicts that matter flows away from under-dense regions to produce the voids, with galaxies then forming on the void edges.

The volume fraction of voids thus grows as the Universe expands.

Negative curvature in the empty voids changes the predicted brightness of standard candles, and angular sizze of standard rulers, which can be measured as functions of redshift.

Lucy worked out these pedictions for the Timescape model with no DE, as well as for several standard cosmological models that include DE.

By fitting to the latest observations, she found that Timescape predictions remove the need for DE when applied separately to the standard candles and standard rulers.

However, these two tests required a somewhat different void volume fraction.

Further investigation is underway as Lucy prepares her findings for publication.

 

 

Zheqi Liu  - Astrophysics BSc Project Prize

(graduated in absentia)

Exploring the Impact of Hidden Stellar Companions on Atmospheric Characterisation of Hot Jupiters

Supervisor: Ryan MacDonald

Zheqi Liu's Astrophysics BSc project sought an answer to the question of how the atmospheric spectrum of a hot giant exoplanet would be altered if an unknown 'hidden' star was present nearby in the sky. She simulated the starlight filtering through the atmosphere of an exoplanet with and without a hidden stellar companion and, through rigorous Bayesian analysis, showed that our measurements of the planet's chemical composition can be dramatically thrown off if we don't know about such a hidden star. Her most exciting result is that we can use the subtle distortion of the planet's spectrum in the near-infrared, as seen by the James Webb Space Telescope, to figure out that a hidden star is present and hence reliably measure the planet's atmospheric composition. We are continuing to work together to prepare her project results for submission to a journal.