Researchers develop light emitter for quantum circuits

Researchers from the KTH Royal Institute of Technology (KTH) have developed a method of emitting light for use in quantum circuits.

The application of a quantum internet is dependent on being able to harness light to transmit information over fibre optic networks. Now, researchers in Sweden have potentially made advancements in this challenge; they have built integrated chips that can generate light particles on demand without needing extreme refrigeration.

Quantum computing is reliant on electrons that carry qubits of information to execute different calculations at the same time, in a fraction of the time it takes conventional computers.

Val Zwiller, Professor at KTH, and co-author of the research, explained that to flawlessly assimilate quantum computing and fibre optic networks – which are currently used for the internet – it would be more favourable to utilise optical photons.

“The photonic approach offers a natural link between communication and computation,” he said. “That is important since the end goal is to transmit the processed quantum information using light.”

To facilitate the ability of photons to deliver qubits on-demand in quantum systems, it is necessary that they are emitted in a deterministic approach. This can be achieved at exceptionally low temperatures in artificial atoms, but now the researchers have reported a way to achieve this at room temperature in optical integrated circuits.

This novel approach allows for photon emitters to be accurately positioned in integrated optical circuits that are reminiscent of copper wires for electricity, but instead, they carry light explained co-author of the research, Ali Elshaari, Associate Professor at KTH.

The team channelled the single-photon-emitting properties of hexagonal boron nitride (hBN), a layered material. hBN is a compound frequently used for applications such as ceramics, alloys, resins, plastics and rubbers to give them self-lubricating properties. They combined the material with silicon nitride waveguides to guide the emitted photons.

Quantum circuits with light are usually operated at cryogenic temperatures using atom-like single-photon sources, or at room temperature using random single-photon sources, Elshaari added. Contrasting the typical methods, the approach created at KTH facilitates optical circuits with on-demand emission of light particles at room temperature.

“In existing optical circuits operating at room temperature, you never know when the single photon is generated unless you do a heralding measurement,” Elshaari said. “We realised a deterministic process that precisely positions light-particles emitters operating at room temperature in an integrated photonic circuit.”

The group recalled pairing the hBN single-photon emitter to silicon nitride waveguides, and they established a technique to image the quantum emitters. Then, taking a hybrid approach, they developed the photonic circuits with consideration to the quantum sources locations by using a combination of steps containing electron beam lithography and etching, while maintaining the high quality of the quantum light.

The researcher’s development could lead to a process called hybrid integration, which means that it could be possible to incorporate atom-like single-photon emitters into photonic platforms that cannot emit light effectively on demand.

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