Silicon photonics for large-scale quantum information applications

Researchers from STMicroelectronics, the Centre for Nanosciences and Nanotechnology (C2N) and Télécom Paris have developed silicon ring resonators with a footprint smaller than 0.05 mm² that is capable of generating over 70 distinct frequency channels spaced 21 GHz apart. This development could lead to significant advancements in quantum computing and also lays the groundwork for ultra-secure communications networks.

Integrated photonics, the manipulation of light within tiny circuits on silicon chips, holds promise for quantum applications due to its scalability and compatibility with existing telecommunications infrastructure. The new development allows for the parallelisation and independent control of 34 single qubit-gates using three standard electro-optic devices. The device can efficiently generate frequency-bin entangled photon pairs that are readily manipulable — critical components in the construction of quantum networks.

The key innovation lies in their ability to exploit these narrow frequency separations to create and control quantum states. Using integrated ring resonators, the researchers successfully generated frequency-entangled states through a process known as spontaneous four-wave mixing. This technique allows photons to interact and become entangled, a crucial capability for building quantum circuits.

The new development is also scalable; by leveraging the precise control offered by the silicon resonators, the researchers demonstrated the simultaneous operation of 34 single qubit-gates using three off-the-shelf electro-optic devices. This enables the creation of complex quantum networks where multiple qubits can be manipulated independently and in parallel.

To validate their approach, the researchers performed experiments at C2N that showed quantum state tomography on 17 pairs of maximally entangled qubits across different frequency bins. This detailed characterisation confirmed the fidelity and coherence of their quantum states, marking a step towards practical quantum computing.

The researchers also established what they believe is the first fully connected five-user quantum network in the frequency domain. This could open new avenues for quantum communication protocols, which rely on the secure transmission of information encoded in quantum states.

This research showcases the power of silicon photonics in advancing quantum technologies and also paves the way for future applications in quantum computing and secure communications. With continued advancements, these integrated photonics platforms could enhance industries reliant on secure data transmission, offering higher levels of computational power and data security.

“Our work highlights how frequency-bin can be leveraged for large-scale applications in quantum information. We believe that it offers perspectives for scalable frequency-domain architectures for high-dimensional and resource-efficient quantum communications,” said Dr Antoine Henry, from C2N and Télécom Paris.

The single photons at telecom wavelengths are also suitable for real-world applications harnessing existing fibre-optic networks.

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