Scientists in quantum leap in chip light source

Team in China says the semiconductor gallium nitride may help vastly speed up computation

Researchers in China have moved a step closer to building a quantum chip with the world-first use of a common semiconductor to create a quantum light source.

Quantum chips have the potential to solve complex problems exponentially faster than through conventional, electron-based computation, but scientists have struggled to build the components needed for an integrated circuit.

A team in China now says they created one of those components – a quantum light source – using the semiconductor gallium nitride (GaN), a material used for decades in blue-light-emitting diodes.

The device has “remarkable potential” for building small, robust quantum chips, according to the team from the University of Electronic Science and Technology of China (UESTC), Tsinghua University and the Shanghai Institute of Microsystem and Information Technology.

The light source produced pairs of light particles entangled at the quantum level, that can be used to carry information. Compared with existing quantum light sources based on materials such as silicon nitride and indium phosphide, the new device had a much wider wavelength range and could be used to build other major components of a quantum circuit, the team reported in the journal Physical Review Letters last month.

“We demonstrate that gallium nitride is a good quantum material platform for photonic quantum information, in which the generation of quantum light is crucial,” lead author Zhou Qiang from UESTC told Physics Magazine.

Quantum optics expert Thomas Walther from the Technical University of Darmstadt in Germany told the magazine that the work was “a major step forward” because it could cut the cost of manufacturing such systems and make them much more compact and rugged than they were today.

In their experiment, Zhou and his colleagues first grew a thin film of GaN on a sapphire layer. Then they etched a ring in the film that was 120 micrometres across, allowing light particles from laser beams to travel around the ring.

When the researchers fed infrared laser light into the GaN film, some light particles were trapped and became “resonant” in pairs.

Because of an effect known as spontaneous four-wave mixing, some resonant pairs gave rise to a new pair of light particles that were entangled with each other.

The degree of entanglement produced by the GaN ring was “comparable” to the level measured for other quantum light sources, Zhou told Physics Magazine. The output wavelength range also extended from 25.6 nanometres with previous materials to 100 nanometres with the new device.

“By providing more wavelength resources, we will be able to meet the needs of more users hoping to access a quantum network via different wavelengths,” Zhou told Science and Technology Daily.

Besides the quantum light source, GaN is also a promising material for making other components of a quantum circuit, according to the team.