Ancient Namibian gemstone holds key to future quantum computers

Cuprous Oxide – the crystal mined in Namibia used to make Rydberg Polaritons. Credit: University of St Andrews

A special form of light made from an ancient Namibian gemstone could hold the key to new light-based quantum computers that could solve long-standing scientific mysteries, according to new research from the University of St Andrews .

The research, conducted in collaboration with scientists from Harvard University in the United States, Macquarie University in Australia and Aarhus University in Denmark and published in natural materials, used a naturally extracted cuprous oxide (Cu2O) Gemstone from Namibia to produce Rydberg Polaritons, the largest hybrid particles of light and matter ever created.

Rydberg’s polaritons continuously pass from light to matter and vice versa. In Rydberg polaritons, light and matter are like two sides of a coin, and the matter side is what makes the polaritons interact.

This interaction is crucial because it is what allows the creation of quantum simulators, a special type of quantum computer, where information is stored in quantum bits. These quantum bits, unlike the binary bits of classical computers which can only be 0 or 1, can take on any value between 0 and 1. They can therefore store much more information and carry out several processes simultaneously.

This capability could allow quantum simulators to solve important mysteries in physics, chemistry and biology, for example, how to make high-temperature superconductors for high-speed trains, how to make cheaper fertilizers that could solving world hunger, or how proteins fold to facilitate producing more effective drugs.

Project leader Dr Hamid Ohadi, from the School of Physics and Astronomy, University of St Andrews, said: “Making a quantum simulator out of light is the holy grail of science. We took a big step towards that by creating the Rydberg Polaritons, the key ingredient in this one.

To create Rydberg polaritons, the researchers trapped light between two highly reflective mirrors. A cuprous oxide crystal from a stone quarried in Namibia was then thinned and polished into a plate 30 micrometers thick (thinner than a human hair) and sandwiched between the two mirrors to render the polaritons of Rydberg 100 times larger than ever before.

One of the lead authors, Dr Sai Kiran Rajendran, from the School of Physics and Astronomy, University of St Andrews, said: “Buying the stone on eBay was easy. The challenge was to make Rydberg polaritons that exist in an extremely narrow color gamut.

The team is currently refining these methods to explore the possibility of fabricating quantum circuits, which are the next ingredient in quantum simulators.

Reference: “Rydberg exciton–polaritons in a Cu2O microcavity” by Konstantinos Orfanakis, Sai Kiran Rajendran, Valentin Walther, Thomas Volz, Thomas Pohl and Hamid Ohadi, April 14, 2022, Natural materials.
DOI: 10.1038/s41563-022-01230-4

The research was funded by the UK Engineering and Physical Sciences Research Council (EPSRC).