An international team of researchers has succeeded in producing Rydberg polaritons from an ore containing copper oxide crystals from an ancient deposit in Namibia. The resulting particles are the largest hybrid particles of light and matter ever created and could hold the key to new light-based quantum computers.
Atoms can interact with each other but move very slowly while photons move quickly but do not interact with each other. However, producing optical photons and allowing them to interact in a controlled manner are two necessary prerequisites for the development of long-range quantum communications, and more generally for the quantum processing of information encoded on photons.
To achieve this goal, one approach is to create hybrid particles, both matter and light, called Rydberg polaritons; these quasi-particles continuously move from light to matter and vice versa. A team now reports that they created such particles using a crystal of copper oxide (Cu2O). Their work represents a real breakthrough: the interactions between polaritons are essential for creating quantum simulators that could solve the greatest mysteries of science.
Causing interactions between photons
† Making a quantum simulator with light is the holy grail of science † Hamid Ohadi said in a statement:, a physicist at the University of St Andrews in the United Kingdom and co-author of the study presenting this work. A quantum simulator is a special type of quantum computer that controls the interactions between quantum bits (qubits) so that it can simulate certain quantum problems that are particularly difficult to model. In other words, a simulator is more specific than a quantum computer – it should be able to solve any type of problem.
In Rydberg polaritons, light and matter are like two sides of a coin, the researchers explain; it is the matter side that causes the polaritons to interact with each other. They are formed by the coupling of excitons and photons. To produce them, the researchers used a gemstone (called cuprite) that contains copper oxide, because this material is a powerful superconductor when cooled to a critical temperature. Previous research had also shown that copper oxide contained “giant” Rydberg excitons, on the order of a micrometer — a dimension that favors interactions.
Excitons are electrically neutral quasi-particles – which can be thought of as an electron-electron-hole pair, bound by Coulomb forces – that can couple with light particles under the right conditions. For example, the copper oxide excitons can be coupled to photons, in a device called the Fabry-Perot interferometer, consisting of two planar and parallel semi-reflective mirrors, with high reflection coefficients. In this interferometer, the incoming light makes several round trips in the optical cavity and partially comes out with each reflection, with the outgoing rays interfering with each other.
The researchers used such a device to make the Rydberg polaritons. The copper oxide crystal, taken from a stone quarried from an ancient cuprite deposit in Namibia, was thinned and polished to obtain a plate 30 micrometers thick (thinner than a strand of human hair!); this plate was then inserted between the two highly reflective mirrors.
The foundation of future quantum circuits
Thanks to their new device, the team has obtained Rydberg polaritons with a diameter of 0.5 m, which is 100 times larger than the ones obtained so far! † Buying the stone on eBay was easy. The challenge was to create Rydberg polaritons that exist in an extremely narrow color gamut emphasizes the physicist Sai Kiran Rajendran, of the University of St Andrews and co-author of the study. The goal has been achieved and this work lays the foundation for future high computational quantum circuits.
By bringing together the interaction possibilities of matter and the speed of light particles, quantum simulators can solve important mysteries in physics, chemistry and biology that today’s computers cannot solve. In particular, the researchers refer to the development of high-temperature superconductors for high-speed trains; this technology could also help to better understand how proteins fold, facilitating the production of more effective drugs.
The team is currently continuing their research to explore the possibility of controlling these polaritons to fabricate quantum circuits, the next ingredient of quantum simulators. † These results open the way to the realization of highly interacting exciton polaritons and the exploration of highly correlated phases of matter using light on a chip. summarize the researchers Natural materials†
