Large-scale silicon quantum photonics implementing arbitrary two-qubit processing (1809.09791v1)

Abstract: Integrated optics is an engineering solution proposed for exquisite control of photonic quantum information. Here we use silicon photonics and the linear combination of quantum operators scheme to realise a fully programmable two-qubit quantum processor. The device is fabricated with readily available CMOS based processing and comprises four nonlinear photon-sources, four filters, eighty-two beam splitters and fifty-eight individually addressable phase shifters. To demonstrate performance, we programmed the device to implement ninety-eight various two-qubit unitary operations (with average quantum process fidelity of 93.2$\pm$4.5%), a two-qubit quantum approximate optimization algorithm and efficient simulation of Szegedy directed quantum walks. This fosters further use of the linear combination architecture with silicon photonics for future photonic quantum processors.

• The paper demonstrates a fully programmable two-qubit quantum processor fabricated using CMOS-based silicon photonics.
• It implements 98 two-qubit operations with an average fidelity of 93.2%, including CNOT gates reaching 98.85% fidelity.
• The device runs advanced quantum algorithms such as QAOA and Szegedy walks, underscoring the scalability of photonic quantum technology.

Large-Scale Silicon Quantum Photonics: Arbitrary Two-Qubit Processing

The discussed paper focuses on implementing a fully programmable two-qubit quantum processor using large-scale silicon quantum photonics. The authors utilize the linear combination of quantum operators scheme to create a device fabricated with standard CMOS-based processes, which includes various integrated components necessary for quantum information processing (QIP).

This silicon photonic device integrates four nonlinear photon sources, four filters, eighty-two beam splitters, and fifty-eight individually addressable phase shifters. Its architecture enables the realization of arbitrary two-qubit unitary operations with an average quantum process fidelity of 93.2%. Among the 98 different two-qubit operations implemented, common gates like the CNOT demonstrated process fidelities as high as 98.85%.

The device demonstrates its capability by executing a two-qubit quantum approximate optimization algorithm (QAOA) and simulating Szegedy directed quantum walks, showcasing the utility of silicon photonics in performing complex quantum algorithms. It highlights the practical viability of using silicon photonics for constructing more sophisticated photonic quantum processors.

From a theoretical perspective, these results reinforce the potential of silicon photonics as a scalable platform for quantum computing. The combination of high-fidelity operation and CMOS-compatible fabrication positions this technology as a formidable contender in the ongoing development of practical quantum computing solutions. Although the current implementation is limited by the exponential growth of components with the number of qubits, advancement in silicon photonics and integrated optics may mitigate these challenges and lead to more scalable solutions.

Future research directions include exploring optimizations in silicon photonics and refining the integration of components such as on-chip detection and multi-photon sources. Such enhancements could further improve the performance and scalability of photonic quantum technologies, bringing us closer to practical, universal quantum computing systems.