One step closer to new devices for quantum computing

New research from Penn Engineering describes a new type of ‘quasiparticle’ and topological insulator, opening up new opportunities and future applications into new photonic devices.

Quantum devices have the potential to revolutionize computing but there are still a number of practical limitations and hurdles. One challenge is that qubits, the basic unit of quantum information, are fragile, so quantum devices can only be used at extremely low temperatures.

On the left, an image of the Agarwal group’s device, a single layer of tungsten disulfide (WS2) on a periodically patterned photonic crystal, On the right, the bright spot is circularly polarized light exciting helical topological exciton-polaritons. — On the left, an image of the Agarwal group’s device, a single layer of tungsten disulfide (WS2) on a periodically patterned photonic crystal. Strong coupling between the excitons of WS2 with the photonic crystal leads to the formation of exciton-photon polaritons with helical topological properties. On the right, the bright spot is circularly polarized light exciting helical topological exciton-polaritons, which have a particular spin and propagate forward, bending around sharp corners with no backscattering. (Image: Penn Engineering Today)

To help address this challenge, researchers are evaluating new types of “quasiparticles,” phenomena that appear to have properties of different particles combined together. Finding ways to both achieve and control the right combination of properties, such as mass, speed, or direction of motion, would these types of particles to be more broadly used. Examples of these quasiparticles include excitons, which act like an electron bound to an empty space in a semiconducting material. Another example moving one step up is an exciton-polariton, one that combines the properties of an exciton with that of a photon and subsequently behaves like a combination of both matter and light.

Researchers at Penn’s School of Engineering and Applied Science have created a new and exotic form of an exciton-polariton, one that has a defined quantum spin that is locked to its direction of motion. In a study recently published in Science, the researchers found that, depending on the direction of the quasiparticle’s spin, these helical topological exciton-polaritons move in opposite directions along the surface of a newly developed topological insulator, materials with a conductive surface and an insulating core, that was also developed as part of this study. The research was led by Ritesh Agarwal, professor in the Department of Materials Science and Engineering, and Wenjing Liu, a postdoctoral researcher in his lab, in collaboration with researchers at Hunan University and George Washington University.

The researchers also found that this approach works at warmer, more user-friendly conditions, with this study conducted at 200 Kelvin, or roughly -100F, as compared to similar systems that operate at 4K, or roughly -450F. This opens up the possibility of using these new quasiparticles and topological insulators to transmit information or perform computations at unprecedented speeds. The researchers are confident that further research and improved fabrication techniques will allow their design to operate at room temperature.