The promise of a quantum Internet depends on the complexity of harnessing light to transmit quantum information over fiber-optic networks. A potential step forward has been reported today by Swedish researchers who have developed integrated chips capable of generating light particles on demand and without resorting to extreme refrigeration.
Quantum computing today relies on states of matter, that is, electrons that carry qubits of information to perform multiple calculations simultaneously, in a fraction of the time it takes with classical computing. .
Research co-author Val Zwiller, a professor at the KTH Royal Institute of Technology, says that to seamlessly integrate quantum computing with fiber-optic networks – which are used by the Internet today – a more promising approach would be to exploit optical photons.
“The photonics approach offers a natural link between communication and computation,” he says. “This is important, because the end goal is to transmit the processed quantum information using light.”
But for photons to deliver qubits on demand in quantum systems, they must be emitted deterministically rather than probabilistically. This can be accomplished at extremely low temperatures in man-made atoms, but today the KTH research group reported a way to make it work in optical integrated circuits – at room temperature.
The new method allows photon emitters to be precisely positioned in integrated optical circuits that look like copper wires for electricity, except that they carry light instead, explains the co-author of the research, Ali Elshaari, associate professor at KTH Royal Institute of Technology.
The researchers exploited the single-photon-emitting properties of hexagonal boron nitride (hBN), a layered material. HBN is a compound commonly used in ceramics, alloys, resins, plastics and rubbers to give them self-lubricating properties. They embedded the material with silicon nitride waveguides to direct the emitted photons.
Quantum circuits with light operate either at cryogenic temperatures – plus 4 Kelvin above absolute zero – using single atom-shaped photon sources, or at room temperature using single-photon random sources, Elshaari says. . On the other hand, the technique developed at KTH allows 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 being generated unless you do an heralding measurement,” Elshaari explains. “We have performed a deterministic process that precisely positions emitters of light particles operating at room temperature in an integrated photonic circuit.”
The researchers reported the coupling of a single hBN photonic emitter to silicon nitride waveguides, and they developed a method to image quantum emitters. Then, in a hybrid approach, the team built the photonic circuits relative to the locations of the quantum sources using a series of steps involving lithography and electron beam etching, while preserving the high-quality nature of quantum light.
This achievement paves the way for hybrid integration, that is, the incorporation of atom-like single-photon emitters into photonic platforms that cannot efficiently emit light on demand.
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