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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Practical Quantum Communication and Processing

Fabio Antonio Bovino

Published Jun 21, 2021• 0 citations
Publisher

Abstract

Nanophotonics offers the platform for large-scale implementation of quantum processors. A number of groundbreaking experiments of quantum information processing, based on bosonic interference, have recently been realized. The most important issues are the practical scalability of quantum circuits, the ability to perform quantum logic gates with error rates below the fault-tolerant threshold, and the incorporation into large-scale quantum circuits with realistic physical resources and single-photon detectors packed on an optical chip.

DOI
10.1109/cleo/europe-eqec52157.2021.9542352

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Nanophotonics offers the platform for large-scale implementation of quantum processors. A number of groundbreaking experiments of quantum information processing, based on bosonic interference, have recently been realized. The most important issues are the practical scalability of quantum circuits, the ability to perform quantum logic gates with error rates below the fault-tolerant threshold, and the incorporation into large-scale quantum circuits with realistic physical resources and single-photon detectors packed on an optical chip.
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Quantum information processing holds great promise for communicating and computing data efficiently. However, scaling current photonic implementation approaches to larger system size remains an outstanding challenge for realizing disruptive quantum technology. Two main ingredients of quantum information processors are quantum interference and single-photon detectors. Here we develop a hybrid superconducting-photonic circuit system to show how these elements can be combined in a scalable fashion on a silicon chip. We demonstrate the suitability of this approach for integrated quantum optics by interfering and detecting photon pairs directly on the chip with waveguide-coupled single-photon detectors. Using a directional coupler implemented with silicon nitride nanophotonic waveguides, we observe 97% interference visibility when measuring photon statistics with two monolithically integrated superconducting single-photon detectors. The photonic circuit and detector fabrication processes are compatible with standard semiconductor thin-film technology, making it possible to implement more complex and larger scale quantum photonic circuits on silicon chips.
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A major challenge in practical quantum computation is the ineludible errors caused by the interaction of quantum systems with their environment. Fault-tolerant schemes, in which logical qubits are encoded by several physical qubits, enable to the output of a higher probability of correct logical qubits under the presence of errors. However, strict requirements to encode qubits and operators render the implementation of a full fault-tolerant computation challenging even for the achievable noisy intermediate-scale quantum technology. Especially the threshold for fault-tolerant computation still lacks experimental verification. Here, based on an all-optical setup, we experimentally demonstrate the existence of the threshold for the fault-tolerant protocol. Four physical qubits are represented as the spatial modes of two entangled photons, which are used to encode two logical qubits. The experimental results clearly show that when the error rate is below the threshold, the probability of correct output in the circuit, formed with fault-tolerant gates, is higher than that in the corresponding non-encoded circuit. In contrast, when the error rate is above the threshold, no advantage is observed in the fault-tolerant implementation. The developed high-accuracy optical system may provide a reliable platform to investigate error propagation in more complex circuits with fault-tolerant gates.