Near perfect two-photon interference out a down-converter on a silicon photonic chip

Abstract

Integrated entangled photon-pair sources are key elements for enabling large-scale quantum photonic solutions, and addresses the challenges of both scaling-up and stability. Here we report the first demonstration of an energy-time entangled photon-pair source based on spontaneous parametric down-conversion in silicon-based platform through an optically induced second-order (𝜒 (2) ) nonlinearity, ensuring type-0 quasi-phase-matching of fundamental harmonic and its second-harmonic inside the waveguide. The developed source shows a coincidence-toaccidental ratio of 1635 at 8 of 𝜇W pump power. Remarkably, we report two-photon interference with near-perfect visibility of 99.36±1.94%, showing high-quality photonic entanglement without excess background noise. This opens a new horizon for quantum technologies requiring the integration of a large variety of building functionalities on single chips.Quantum science benefits from a worldwide research effort for developing disruptive technique finding repercussion in communication and processing of information. The realization of flexible, scalable and operational devices in quantum technologies and systems requires new approaches for hardware components. Integrated quantum photonics addresses the challenges of both scaling-up and stability, enabling the realization of key physical resources, such as on-chip photon pair generators, filters, modulators and detectors, and especially their interconnects, leading the quest for advanced large-scale monolithic devices [1,2]. The range of desired building functions, each performing a special task, has motivated the emergence of hybrid platforms combining the best of different photonic technologies, including 𝜒 (2) and 𝜒 (3) nonlinearities based platforms [3,4] in single functional chips [5][6][7][8]. The price to pay lies in the complex hybrid integration of each elementary building blocks revealing new technological issues, such as excessive optical losses due to transitions [9]. An elegant solution, still keeping additional benefits of merging 𝜒 (2) -and 𝜒 (3) -nonlinearities based platforms, without compromising the overall functionality of the single device, lies in inducing an effective 𝜒 (2) nonlinearity in a silicon (Si)-based chip.Among multiple physical approaches, the Si-based technology remains an outstanding option due to ubiquitous capabilities developed by the microelectronics industry. While the linear circuitry in Si photonics is well established, achieving flexible, efficient and integrated quantum sources that would allow entangled photon-pair generation has remained challenging [8,10]. The latter is essential for further advances of photonic quantum devices and applications [11]. The creation of entangled photons in Si-based devices is naturally obtained through spontaneous four-wave mixing (SFWM), which generates photonic noise, degrading the overall system's performance. Recent publications show that the ability to detect photon correlations (entanglement) is limited by spurious effects such as two-photon and f...

Coherent Photogalvanic Effect for Second-Order Nonlinear Photonics

“…It is exploited for several linear [25] and nonlinear applications, such as four-wave mixing [26,27], third-harmonic generation (THG) [28], supercontinuum [29] and Kerr comb [30] generation using χ (3) nonlinearity. AOP now allows to add χ (2) processes, such as SHG, differencefrequency generation [31] and spontaneous parametric down-conversion [32], to the already impressive nonlinear toolbox of Si 3 N 4 . Recently, there have been several qualitative attempts to explain the time dynamics of AOP, which exhibits growth and saturation, and its dependence on waveguide dimensions [21,22,33].…”