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Optica

Micrometer-scale integrated silicon source of time-energy entangled photons

Davide Grassani, Stefano Azzini, Marco Liscidini, Mattéo Galli, Michael John Strain, Marc Sorel, John E. Sipe, Daniele Bajoni

Published Jan 26, 2015• 263 citations
Publisher

Abstract

Entanglement is a fundamental resource in quantum information processing. Several studies have explored the integration of sources of entangled states on a silicon chip, but the devices demonstrated so far require millimeter lengths and pump powers of the order of hundreds of milliwatts to produce an appreciable photon flux, hindering their scalability and dense integration. Microring resonators have been shown to be efficient sources of photon pairs, but entangled state emission has never been proven in these devices. Here we report the first demonstration, to the best of our knowledge, of a microring resonator capable of emitting time-energy entangled photons. We use a Franson experiment to show a violation of Bell’s inequality by more than seven standard deviations with an internal pair generation exceeding 107 Hz. The source is integrated on a silicon chip, operates at milliwatt and submilliwatt pump power, emits in the telecom band, and outputs into a photonic waveguide. These are all essential features of an entangled state emitter for a quantum photonic network.

DOI
10.1364/optica.2.000088

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Entanglement is a fundamental resource in quantum information processing. Several studies have explored the integration of sources of entangled states on a silicon chip, but the devices demonstrated so far require millimeter lengths and pump powers of the order of hundreds of milliwatts to produce an appreciable photon flux, hindering their scalability and dense integration. Microring resonators have been shown to be efficient sources of photon pairs, but entangled state emission has never been proven in these devices. Here we report the first demonstration, to the best of our knowledge, of a microring resonator capable of emitting time-energy entangled photons. We use a Franson experiment to show a violation of Bell’s inequality by more than seven standard deviations with an internal pair generation exceeding 107 Hz. The source is integrated on a silicon chip, operates at milliwatt and submilliwatt pump power, emits in the telecom band, and outputs into a photonic waveguide. These are all essential features of an entangled state emitter for a quantum photonic network.
Entanglement is a fundamental resource in quantum information processing. Several studies have explored the integration of sources of entangled states on a silicon chip but the sources demonstrated so far require millimeter lengths and pump powers of the order of hundreds of mWs to produce an appreciable photon flux, hindering their scalability and dense integration. Microring resonators have been shown to be efficient sources of photon pairs, but entangled state emission has never been demonstrated. Here we report the first demonstration of a microring resonator capable of emitting time-energy entangled photons. We use a Franson experiment to show a violation of Bell's inequality by as much as 11 standard deviations. The source is integrated on a silicon chip, operates at sub-mW pump power, emits in the telecom band with a pair generation rate exceeding 107^77 Hz per nmnmnm, and outputs into a photonic waveguide. These are all essential features of an entangled states emitter for a quantum photonic networks.
Entangled photon-pair sources are essential components for emerging quantum information-processing technologies. Among various platforms, on-chip microresonators offer strong potential due to their resonant enhancement and suitability for wafer-scale integration. In this study, we demonstrate ultrabright entangled photon-pair generation from high- Q silicon microring resonators. By optimizing the device geometry and coupling configuration to suppress sidewall scattering and selectively excite the fundamental mode, we achieve single-mode resonance with an intrinsic Q -factor of 1.26 × 10 6 using only standard fabrication processes available in CMOS foundries. The resulting high- Q resonator yields a record-high brightness coefficient of 3.9 × 10 9 Hz/GHz/mW 2 . At an on-chip pump power of 240 μW, we obtain a maximum brightness of 22.0 MHz/GHz and a maximum photon-pair generation rate of 9.19 MHz. At a low-pump power of 10 μW, Franson-type two-photon interference exhibits a visibility of 98.0 ± 0.2%, confirming high-quality time–energy entanglement. These results show that narrow bandwidth and high generation rate can be achieved simultaneously in CMOS-compatible silicon photonic sources, thereby advancing their use in quantum repeaters and scalable quantum networks.
An integrated source of time-energy entangled photons is demonstrated through resonantly enhanced spontaneous four-wave mixing in a silicon micro-ring resonator. A Franson type set-up is employed to show the quantum interference between photon pairs with a visibility exceeding 90% and a violation of the Bell's inequality by more than 10 standard deviations. The high spectral brightness and the extremely small footprint of our source make it suitable for the development of quantum information protocols integrated on chip.
Integrated quantum photonics leverages the on-chip generation of nonclassical states of light to realize key functionalities of quantum devices. Typically, the generation of such nonclassical states relies on whispering gallery mode resonators, such as integrated optical micro-rings, which enhance the efficiency of the underlying spontaneous nonlinear processes. While these kinds of resonators excel in maximizing either the temporal confinement or the spatial overlap between different resonant modes, they are usually associated with large mode volumes, imposing an intrinsic limitation on the efficiency and footprint of the device. Here, we engineer a source of time-energy entangled photon pairs based on a silicon photonic crystal cavity, implemented in a fully CMOS-compatible platform. In this device, resonantly enhanced spontaneous four-wave mixing converts pump photon pairs into signal/idler photon pairs under the energy-conserving condition in the telecommunication C-band. The design of the resonator is based on an effective bichromatic confinement potential, allowing it to achieve up to nine close-to-equally spaced modes in frequency, while preserving small mode volumes, and the whole chip, including grating couplers and access waveguides, is fabricated in a single run on a silicon-on-insulator platform. Besides demonstrating efficient photon pair generation, we also implement a Franson-type interference experiment, demonstrating entanglement between signal and idler photons with a Bell inequality violation exceeding five standard deviations. The high generation efficiency combined with the small device footprint in a CMOS-compatible integrated structure opens a pathway toward the implementation of compact quantum light sources in all-silicon photonic platforms.
Integrated time-bin-entangled photon-pair source with cavity-enhanced nonlinear optical processes is essential for quantum information technologies. However, microcavities with a high quality factor inherently introduce a trade-off between generation efficiency and photon bandwidth, which hinders the development of high-speed quantum networks with an integrated source. Here, we address this challenge by optimizing the nonlinearity property of the material and the geometry of the integrated microring resonator with a 4H-silicon carbide platform. Operating at a loaded quality factor of 1.9 ×\times× 10^5 - spectral bandwidth of 1.0 GHz and pumped with 300-ps double pulses separated by 1.25 ns at a repetition rate of 160 MHz, the device achieves a time-bin-entangled photon-pair generation rate of 1.35 ×\times× 10^7 s^-1 mW^-2. A raw visibility of 95.55 ±\pm± 0.18% is measured, showing a violation of Bell's inequality by more than 138 standard deviations, and a fidelity of 94.37 ±\pm± 0.22% is obtained by quantum state tomography. These results provide a scalable pathway to an efficient and broadband time-bin entangled quantum light source, overcoming intrinsic limitations of cavity-based designs and advancing integrated platforms for future quantum communication networks.