Projects

Majorana fermions are exciting for fundamental condensed matter theorists and for material applications in quantum computing. In this project we focus on extending theoretical understanding of Majoranas in aperiodic Kitaev chain models. We look at a range of sequences which are used to generate 1D quasicrystals, and explore their potential for realising Majoranas. We find differing characteristics depending on the underlying sequence, and aim to show a novel observation that the topological phase transition inherets the fractal structure of the quasicrystal.

Ion trapping is one of the most competitive quantum computing architectures right now. It involves confining ions electromagnetic fields and lasers to cool and manipulate their states. Benchtop optics involves a high degree of precision and its performance is susceptible to environmental factors. This makes equipment setup and maintenance a difficult and time-intensive task.

At the National Quantum Computing Centre (NQCC) I created a suite of automated routines to align and calibrate the laser systems in their ion trapping experiment. This greatly reduced the time taken to set up and maintain the experiment, and has improved its overall performance and reliability.

This involved a lot of interesting machine learning techniques, implemented at a low level using the ARTIQ real-time control environment. There were further challenges around modelling the hysteresis characteristic of the piezoelectric actuators used to make the system robust.

The critical superconducting temperature, and further the phase of cuprate materials depends intrinsically on p-doping levels. Calcium can be used to dope YBCO with holes, this permits experimental exploration of the phase diagram.

The problem is the process of doping YBCO with calcium is difficult to control, and can lead to inhomogeneous samples. Moreover, literature on such experiments often only quoted the Ca concentration of the precursor materials, and failed to report on the final uptake and its homogeneity.

We employed scanning electron microscopy (SEM) to map the calcium distribution in a series of YBCO samples doped with varying levels of calcium. SEM imaging provided the basis of morphological analysis of surface calcium defects, and EDX mapping allowed for further quantitative analysis via the global spatial correlation coefficient and Moran's I coefficient.

Quantum Key Distribution (QKD) leverages truly quantum behaviour to enable secure communication. The particular protocol developed at KETs is implemented on integrated photonics chips (PICs). PICs enable compact and efficient optical circuits, used here to encode and decode messages. However, the small scale of these devices and sensitivity of the signals passing through them mean manufacturing imperfections have a significant impact on their functionality. Therefore, calibrating each PIC is necessary for use in QKD.

In this project I developed and implemented optimisation algorithms to automate the calibration of phase shifters in a cascade of Mach-Zehnder interferometers (MZIs) on the PIC.