Fellowship: PHOCIS- A Photonic Crystal Integrated Squeezer

In recent decades, physicists have increasingly understood that the ability to control quantum systems will unleash powerful enhancements across a range of technologies, eclipsing the best known classical algorithms for a plethora of important computational problems and overcoming classical limits in measurement, sensing and imaging.

At the level of individual photons, light is also governed by the rules of quantum mechanics. As our ability to generate, control, and measure light progresses, so grows our understanding of its potential as a platform for harnessing quantum phenomena for practical purposes. Quantum optics has already delivered advantages in our ability to observe the distant universe and solve mathematical problems beyond the reach of even the most powerful supercomputers.

These technologies demand a source of light into which quantum information can be encoded. Light from so-called "classical" sources, such as lasers, is suboptimal for many measurement or communication tasks and unsuitable for quantum computing. Therefore, new sources of "nonclassical" light are required to unlock the door to the great prizes of quantum technology.

In this fellowship, I will build a source of a type of nonclassical light called "squeezed vacuum". This state of light, characterised by photons appearing in pairs, has already proven pivotal in these existing demonstrations of quantum advantage.

A crucial improvement over earlier technology is that this source will be fabricated directly inside a single piece of optical fibre. This will help minimise the destructive losses which prevent other squeezed vacuum sources being put to use. This device will incorporate some of the newest advances in fibre optics: Firstly, "photonic crystal fibre", developed at the University of Bath, allows careful control over critical properties necessary for the generation of nonclassical light. Secondly, the fibre itself will be modified by exposure to a laser beam, making it reflective. This will allow us to create a light-trap inside the fibre, greatly enhancing the interaction that generates squeezed vacuum.

In the second phase of the project, I will integrate this source with control systems to allow real-time, active manipulation of the output light. I will then route this output into new types of detector with the ability to measure quantum correlations in the beam in real time. By enabling active feedback between the control and detection stages of this system, I aim to bring together the elements necessary for "measurement-based quantum computing"- a practical framework for realising the full potential of quantum information processing.

As a bonus, this research will have a wider impact beyond quantum computing, with the methods developed applicable to new sources of classical light and advancing fields such as spectroscopy and imaging.