University of Bath

Quantum optics

We study and control the most fundamental properties of light.

Photograph of a single photon source built with optical fibre
The optical fibre that we fabricate enables us to build high-performance single-photon sources

The fundamental unit of light is the photon. We carry out research into how we can reliably generate single photons, how we can store them in a memory, and how we can manipulate them to process and transmit quantum information.

Technologies that exploit controlled quantum systems can achieve significant performance enhancements in areas such as computation, communications, and sensing. For example, the current race to scale up towards a fully-programmable quantum computer could result in vast reductions in the time taken to simulate the interactions of large molecules, and commensurate acceleration of pharmaceutical drug development.

Although the beam of light from a laser contains an uncountably large number of photons, making only one is difficult. We achieve this by sending a very bright pulse into an optical fibre, which pulls the electrons in the glass far away from their equilibrium positions. The resulting electron motion produces a pair of new frequencies, meaning that two photons of different colours are emitted. When we detect one of these, we know we must have produced a single, isolated photon at the other frequency. Integrating our sources and detectors with fast optical fibre switch networks enables us to use feed-forward control to enhance the performance of these single-photon sources.

Building a quantum computer based on light requires logic gates, much like those in a conventional computer. However, because photons do not interact with one another, the gates that we can build rely on interference between photons and do not always work. We are building quantum memories that store photons in atomic clouds to be read out later. Long-lived quantum memories can synchronise operations across large-scale networks, enabling the development of more complex quantum processors.