Roadmap on Integrated Quantum Photonics (2102.03323v2)

Abstract: Integrated photonics is at the heart of many classical technologies, from optical communications to biosensors, LIDAR, and data center fiber interconnects. There is strong evidence that these integrated technologies will play a key role in quantum systems as they grow from few-qubit prototypes to tens of thousands of qubits. The underlying laser and optical quantum technologies, with the required functionality and performance, can only be realized through the integration of these components onto quantum photonic integrated circuits (QPICs) with accompanying electronics. In the last decade, remarkable advances in quantum photonic integration and a dramatic reduction in optical losses have enabled benchtop experiments to be scaled down to prototype chips with improvements in efficiency, robustness, and key performance metrics. The reduction in size, weight, power, and improvement in stability that will be enabled by QPICs will play a key role in increasing the degree of complexity and scale in quantum demonstrations. In the next decade, with sustained research, development, and investment in the quantum photonic ecosystem (i.e. PIC-based platforms, devices and circuits, fabrication and integration processes, packaging, and testing and benchmarking), we will witness the transition from single- and few-function prototypes to the large-scale integration of multi-functional and reconfigurable QPICs that will define how information is processed, stored, transmitted, and utilized for quantum computing, communications, metrology, and sensing. This roadmap highlights the current progress in the field of integrated quantum photonics, future challenges, and advances in science and technology needed to meet these challenges.

• The paper outlines a comprehensive analysis of integrated quantum photonic circuits, emphasizing scalable platforms using silicon, lithium niobate, and III-V semiconductors.
• It demonstrates advancements in integrating quantum light sources and detectors, focusing on improving photon indistinguishability and coupling efficiency.
• The paper offers a strategic framework for deploying QPICs in quantum communication, computing, and sensing applications by enhancing photonic-electronic integration.

An Overview of the Journal of Physics: Photonics (2021) Roadmap on Integrated Quantum Photonics

The "Roadmap on Integrated Quantum Photonics" presents a comprehensive examination of the current status, challenges, and future directions of quantum photonic integration. The document emphasizes the potential of Quantum Photonic Integrated Circuits (QPICs) as a transformative platform for advancing the field of quantum information science and technology. This paper assembles insights from a multi-disciplinary team of researchers, providing a systemic outline spanning material science advances, device engineering, and applications in quantum computing and communication.

The roadmap explores the heterogeneous integration for QPICs, underscoring the blending of various materials and technologies to establish scalable, efficient, and versatile photonic circuits. It highlights several material platforms, such as silicon, lithium niobate, III-V semiconductors, and more, that are central to QPICs. These materials are discussed in the context of their suitability for achieving low-loss photonic guiding, efficient nonlinear processes, and electrical to optical interfacing.

With respect to quantum light sources and detectors, the roadmap identifies advancing the integration of reliable quantum dot and color center sources as a strategic thrust, coupled with the integration of high-efficiency detectors like waveguide-integrated superconducting single-photon detectors (SNSPDs). Challenges such as improving photon indistinguishability, minimizing decoherence in solid-state systems, and managing losses at both material and device levels are also addressed.

The paper covers photonic circuit integration with an emphasis on the necessity of robust coupling between photonic and electronic signals to enable quantum information protocols. Various devices including high-performance lasers, modulators, detectors, and nonlinear optics components are discussed, providing domain researchers with critical insight into ongoing developments toward wafer-scale integration. The layout illustrates the enduring issue of coupling efficiency, specifically between free-space inputs and on-chip components, essential for preserving quantum state fidelity in integrated devices.

In addition, the roadmap emphasizes the importance of combining QPICs with current encoding strategies, such as spatial, frequency, and time bins, to fully exploit their high-dimensional capabilities for quantum information processing. Material progress and novel design methodologies for photonic crystal fibers, waveguides, and resonators are showcased in terms of their role in frequency conversion and information processing tasks.

Applications of these integrated systems span quantum communication, computing, and sensing. Practical deployment of QPICs would bolster high-rate quantum key distribution, enable robust qubit networks for quantum processing, and offer enhanced precision in quantum measurement and metrology. The roadmap critiques the continued development of foundational techniques such as error-correction, efficient memory interfaces, and scalable quantum state generation as integral to the realization of functional quantum networks.

Comments on the increasing relevance of machine learning for photonics encapsulate the dynamic intersections of computational techniques with photonic system design. The integration of machine learning algorithms in design, characterization, and operational optimization of QPICs suggests a futuristic blend that could significantly accelerate progress in this domain.

In conclusion, the roadmap articulates a clear path forward in integrated quantum photonics, addressing critical science and technology challenges through a lens focused on collaborative advances across multiple disciplines. It provides a strategic framework for researchers dedicated to producing scalable quantum systems that align with the broad agenda of quantum information science and technology. This comprehensive document serves as an invaluable resource for guiding further research and development efforts in this pivotal domain.