Natural cuprous oxide gemstone.
Giant “atoms” inside a crystal
Semiconductors can host quantum states that closely resemble the energy structure of atoms. These states, known as excitons, provide a unique way to explore atomic physics within a solid.
An exciton is the solid-state analogue of an atom. It consists of an electron and a hole bound together by the Coulomb attraction. As a bound state of a positive and negative charge, excitons exhibit a similar electronic structure to atoms, including a Rydberg series of energy levels. In the photo shown below, each dark line corresponds to an exciton resonance. The pattern of lines looks remarkably similar to an atomic spectrum, with the spectral lines getting closer together as the energy increases.
Spectrally resolved photo revealing the presence of atom-like energy level (excitons, dark bands) in a semiconductor.
The excitons on the right-hand side of the spectrum are particularly interesting. These are Rydberg excitons. In these highly excited states, the average separation between the electron and hole can be larger than a micron.
Why are Rydberg excitons exciting?
The large spatial extent of Rydberg excitons makes them extremely sensitive to small perturbations. They show enhanced sensitivity to electric fields and stronger interactions compared with ground-state excitons. These properties make Rydberg excitons a highly nonlinear system and open up exciting possibilities for studying nonlinear quantum systems.
Our research in Durham explores these possibilities in two different directions:
Rydberg excitons + superconducting circuits
Professor Matt Jones leads a project investigating how Rydberg excitons in Cu2O could be coupled to a superconducting microwave circuit.
Superconducting circuits provide an exceptionally powerful platform for controlling quantum states using microwaves. By coupling them to Rydberg excitons, we aim to create an optical readout of the superconducting circuit, creating a new hybrid quantum system with applications in quantum networking.
Find out more about the Cu2O project
Rydberg excitons + photons
Dr Liam Gallagher leads a project exploring how the strong interactions between Rydberg excitons can be used to make photons interact with one another.
Normally, photons do not interact, making it difficult to use them for quantum information processing. By using Rydberg excitons as an intermediate state, we aim to create effective photon–photon interactions.
This work uses a new material with low optical losses, opening up new opportunities for studying strongly interacting light.
Find out more about the ZnP2 project
Want to do cutting-edge quantum research?
We are always looking for motivated students and postdocs who want to work on challenging problems at the intersection of quantum physics, condensed matter, and photonics.
If you are excited by the idea of exploring new quantum systems, we would love to hear from you.
Contact m.p.a.jones@durham.ac.uk or liam.a.gallagher@durham.ac.uk to find out more.