Hybrid III-V/Silicon Photonics Generate Biphoton States at Rates Above 10s mW for Scalable Quantum Technologies

The demand for compact and scalable photonic technologies drives research into hybrid circuits that combine the best properties of different materials, and a crucial component of these systems is bright, tunable sources of entangled photon pairs. Lorenzo Lazzari, Jérémie Schuhmann, and Othmane Meskine, working at Université Paris Cité and the CNRS, alongside colleagues including Martina Morassi and Aristide Lemaître from Université Paris-Saclay and the CNRS, now demonstrate a significant advance in this field. Their team has created a device that integrates both the generation of entangled photon pairs and the ability to manipulate their properties directly on a single chip. By combining an aluminium gallium arsenide source with a silicon-on-insulator circuit, they achieve a high photon pair generation rate and demonstrate predictable control over the entangled state, paving the way for more complex and compact quantum photonic systems.

Université Côte d’Azur, CNRS, Institut de Physique de Nice, 06200, Nice, France. Hybrid photonic circuits, combining the strengths of different materials, are vital for creating compact, scalable platforms for quantum technologies. A key requirement is the availability of bright sources of tunable entangled photon pairs to support the growing range of quantum applications currently under development. Researchers have now demonstrated a heterogeneously integrated device that merges biphoton generation with on-chip quantum state engineering, combining an aluminum gallium arsenide (AlGaAs) photon-pair source with a silicon-on-insulator (SOI) circuit. This device generates photon pairs and then manipulates their quantum properties directly on the chip, paving the way for more complex quantum circuits and enhancing potential applications in quantum communication, computation, and sensing.

Entangled Photons in Integrated Waveguides

This research focuses on integrated quantum photonics, specifically the generation, manipulation, and detection of entangled photon pairs using AlGaAs-based waveguides and, increasingly, silicon photonics. The overarching goal is to build practical, scalable quantum technologies for applications including secure quantum communication, high-precision quantum metrology, and the building blocks for quantum computing. A significant emphasis is placed on controlling the timing and frequency of photons to enhance quantum performance, and on exploring both continuous-variable and discrete-variable approaches to quantum information processing. The research utilizes AlGaAs Bragg reflection waveguides for generating entangled photons, offering advantages in fabrication, integration, and control.

Silicon photonics is being explored as a complementary platform, offering potential for scalability and cost reduction. The process relies on spontaneous parametric down-conversion (SPDC) to generate entangled photon pairs, and Hong-Ou-Mandel (HOM) interferometry to characterize and manipulate these two-photon states. Researchers are actively improving the performance of HOM interferometry, even in the presence of imperfections. The team manipulates the spectral and temporal properties of photons to optimize entanglement quality and measurement precision, including techniques for compensating for dispersion and shaping photon wavefunctions.

They explore continuous-variable quantum information, encoding quantum information in continuous degrees of freedom like the amplitude and phase of light. Discrete-variable quantum information, encoding information in discrete degrees of freedom like polarization, is also investigated. Dispersion compensation corrects for different wavelengths traveling at different speeds, crucial for maintaining entanglement quality. Bragg gratings control the spectral properties of the generated photons, and researchers are developing electrically injected photon sources for more compact and efficient devices. Specific research goals include improving entanglement quality by generating photons with narrower bandwidths and better timing correlations, mitigating imperfections that degrade entanglement, and engineering the spectral properties of photons for optimal performance.

They aim to achieve measurement precision beyond classical limits using entangled photons, and to explore the use of continuous-variable states for quantum metrology. Optimizing HOM interferometry, improving its visibility and performance, and using it for quantum state tomography are also key objectives. The research focuses on developing integrated photonic circuits that can generate, manipulate, and detect entangled photons, leveraging silicon photonics to reduce cost and complexity. Fundamental studies investigate the properties of entangled photons and the interplay between continuous-variable and discrete-variable quantum information processing, while time-frequency metrology uses time-frequency analysis to characterize and control quantum states of light and improve measurement precision.

Recent developments include significant progress in developing electrically injected photon sources, and increasing focus on integrating AlGaAs components with silicon photonics. Sophisticated techniques are being developed to manipulate the spectral and temporal properties of photons with greater precision, and computational methods are being used to design photonic circuits that meet specific performance requirements. Exploration of new materials and fabrication techniques aims to further improve the performance and scalability of quantum photonic devices. In summary, this research is at the forefront of integrated quantum photonics, with a strong emphasis on practical implementation and scalability, aiming to build robust, efficient, and integrated quantum photonic devices for a wide range of applications.

Hybrid Circuit Generates High-Purity Entangled Photons

Scientists have demonstrated a groundbreaking hybrid photonic circuit that efficiently generates and manipulates entangled photon pairs, essential for advanced quantum technologies. The work merges an aluminum gallium arsenide (AlGaAs) photon-pair source with a silicon-on-insulator (SOI) circuit, achieving high brightness and precise control over the properties of the generated light. This integration leverages the strengths of both materials to create a compact and scalable platform for quantum photonics. The team achieved a photon-pair generation rate exceeding 1,000,000 pairs per second per milliwatt of pump power, a significant advancement in hybrid photonics.

Crucially, the device exhibits a coincidence-to-accidental ratio reaching up to 600, indicating a highly pure source of entangled photons. This performance is achieved through a novel nonlinearly shaped taper design that efficiently transfers photon pairs from the AlGaAs source to the underlying silicon waveguide. Measurements confirm transmission efficiencies of approximately 80% for both polarizations within a 45 nanometer bandwidth centered at 1560 nanometers, a key wavelength for telecommunications. Researchers developed a predictive model to simulate how the geometry of the coupling region influences the joint spectral amplitude (JSA) of the generated biphoton state, both in amplitude and phase.

This allows for precise tailoring of the entanglement properties and spectral bandwidth directly on the chip, eliminating the need for external components. The validity of this model was confirmed through Hong-Ou-Mandel (HOM) interferometry, a standard technique for characterizing entangled photons. This breakthrough delivers a versatile platform for quantum-enhanced metrology and other applications, surpassing the limitations of fully monolithic implementations.

On-Chip Biphoton Generation and Correlation Control

This work demonstrates a hybrid integrated photonic circuit that combines efficient biphoton generation with on-chip control of quantum correlations. Researchers successfully merged an aluminium gallium arsenide source with a silicon-on-insulator circuit, achieving a photon pair generation rate exceeding 10s mW and a high coincidence-to-accidental ratio. Crucially, the design enables predictable manipulation of the biphoton joint spectral amplitude, allowing for complex state engineering directly on the chip. The achievement bridges a gap between hybrid and monolithic semiconductor platforms, offering a new state-of-the-art for on-chip quantum photonics.

By carefully designing the coupling between materials, the team demonstrated precise control over both the amplitude and phase of the generated photon pairs, opening possibilities for advanced quantum metrology and the emulation of exotic particle statistics. While acknowledging that further refinements to coupling design and fabrication could enhance transmission efficiency and polarization insensitivity, the team suggests that inverse design approaches and numerical optimisation of waveguide dispersion represent promising avenues for future research. The broad emission bandwidth and polarization versatility of this hybrid device, combined with potential for electrical pumping, positions it as a strong candidate for robust and scalable quantum technologies, including communication, computation, and precision sensing.