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arXiv:1906.10158 · Optics Express

Mid-infrared quantum optics in silicon

Lawrence M. Rosenfeld, Dominic A. Sulway, Gary F. Sinclair, Vikas Anant, Mark G. Thompson, John G. Rarity, Joshua W. Silverstone

Published Sep 25, 2020• 64 citations
arXivHTMLPDF

Abstract

Applied quantum optics stands to revolutionise many aspects of information technology, provided performance can be maintained when scaled up. Silicon quantum photonics satisfies the scaling requirements of miniaturisation and manufacturability, but at 1.55 µm it suffers from problematic linear and nonlinear loss. Here we show that, by translating silicon quantum photonics to the mid-infrared, a new quantum optics platform is created which can simultaneously maximise manufacturability and miniaturisation, while reducing loss. We demonstrate the necessary platform components: photon-pair generation, single-photon detection, and high-visibility quantum interference, all at wavelengths beyond 2 µm. Across various regimes, we observe a maximum net coincidence rate of 448 ± 12 Hz, a coincidence-to-accidental ratio of 25.7 ± 1.1, and, a net two-photon quantum interference visibility of 0.993 ± 0.017. Mid-infrared silicon quantum photonics will bring new quantum applications within reach.

DOI
10.1364/oe.386615

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Applied quantum optics stands to revolutionise many aspects of information technology, provided performance can be maintained when scaled up. Silicon quantum photonics satisfies the scaling requirements of miniaturisation and manufacturability, but at 1.55 µm it suffers from problematic linear and nonlinear loss. Here we show that, by translating silicon quantum photonics to the mid-infrared, a new quantum optics platform is created which can simultaneously maximise manufacturability and miniaturisation, while reducing loss. We demonstrate the necessary platform components: photon-pair generation, single-photon detection, and high-visibility quantum interference, all at wavelengths beyond 2 µm. Across various regimes, we observe a maximum net coincidence rate of 448 ± 12 Hz, a coincidence-to-accidental ratio of 25.7 ± 1.1, and, a net two-photon quantum interference visibility of 0.993 ± 0.017. Mid-infrared silicon quantum photonics will bring new quantum applications within reach.
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Silicon photonics in the mid-infrared is a promising platform for quantum technologies. Previous demonstrations of silicon mid-infrared quantum optics have used a 340 nm silicon layer height. In this work, we use industry-standard 220 nm silicon to implement a novel, to the best of our knowledge, photon-pair source with a peak coincidence-to-accidental ratio (CAR) of 20.9±2.9 at a net measured rate of 0.63±0.02 Hz and an inferred source efficiency of 2.85±0.04 MHz W −2 . Finally, we report the first integrated mid-infrared entanglement, generating a Bell state with a fidelity of F =94±2%.
Photon-pair sources are essential for complex and scalable quantum photonics circuits. Silicon photonics offers a scalable and low cost platform with a mature fabrication technology for realising this [1] . Recent demonstrations of photon-pair generation and quantum interference in the 2.1 µm band have paved the way towards mid-infrared integrated photon sources [2] , where many gases can be sensed with unique ‘fingerprint’ absorption lines. Producing long wavelength photons with large spectral detunings from the pump, utilising anomalous group-velocity dispersion and type-0 phase matching, is hard due to the highly dispersive nature of nanoscale silicon waveguides.
Abstract Although holding great promise for low noise, ease of operation and networking 1 , useful photonic quantum computing has been precluded by the need for beyond-state-of-the-art components, manufactured by the millions 2–6 . Here we introduce a manufacturable platform 7 for quantum computing with photons. We benchmark a set of monolithically integrated silicon-photonics-based modules to generate, manipulate, network and detect heralded photonic qubits, demonstrating dual-rail photonic qubits with 99.98% ± 0.01% state preparation and measurement fidelity, Hong–Ou–Mandel (HOM) quantum interference between independent photon sources with 99.50% ± 0.25% visibility, two-qubit fusion with 99.22% ± 0.12% fidelity and a chip-to-chip qubit interconnect with 99.72% ± 0.04% fidelity, conditional on photon detection and not accounting for loss. We preview a selection of next-generation technologies: low-loss silicon nitride (SiN) waveguides and components to address loss, as well as fabrication-tolerant photon sources, high-efficiency photon-number-resolving detectors (PNRDs), low-loss chip-to-fibre coupling and barium titanate (BTO) electro-optic phase shifters for high-performance fast switching.
Quantum-optical technologies are transforming communication and metrology by enabling security and sensitivity beyond classical limits. Currently, these technologies are available at visible, near-infrared (NIR) and telecom wavelengths but are strongly underdeveloped at longer wavelengths. There is a growing demand for quantum sources operating in the 2 μm region for various applications. For example, such sources can enable daylight satellite-to-ground based quantum communications by taking advantage of an atmospheric transparency window with reduced solar blackbody radiation compared to telecom wavelengths [1,2,3]. Moreover, squeezed 2 μm sources are expected to have an impact on quantum metrology. For example, in gravitational wave detectors (eg. LIGO), such long wavelengths could reduce the quantum noise and scattering loss from crystalline silicon test masses [4]. Here, we report the generation and characterisation of a photon pair source at 2.080 μm with coincidence-to-accidental ratio (CAR) exceeding 10.
Integrated quantum photonic circuits are a key enabling technology for the scalability of quantum information systems. Among the available platforms, silicon photonics offers an unrivalled capability for the large-scale integration of photonic components within compact footprints. However, the strong index contrast that enables ultra-compact silicon devices also makes them highly sensitive to fabrication imperfections. As circuit complexity increases, active tuning is generally required to maintain spectral alignment among the different components, leading to significant power consumption that ultimately limit scalability. Here, we demonstrate a fully integrated silicon quantum photon-pair source operating without active tuning of any component. The circuit combines photon-pair generation in a micro-ring resonator, pump rejection using Bragg filters, and signal/idler demultiplexing through modal add-drop filters with building blocks engineered to minimize sensitivity to fabrication variations. The resulting circuit achieves excellent experimental quantum performance. Coincidence rates up to 4000 counts s^-1 with coincidence-to-accidental ratios as high as 100 are obtained across the generated spectrum, while separate two-photon interference measurements yield raw visibilities exceeding 93% for individually selected ITU wavelength-channel pairs. By eliminating the need for active spectral tuning while maintaining high quantum performance, this work addresses a major bottleneck in the scaling of complex silicon quantum photonic circuits.