The article comments on a comprehensive review of integrated continuous-variable quantum light sources, high lighting its structured synthesis of recent advances and its relevance to scalable CV quantum computing.
Continuous-variable (CV) quantum light sources are the essential resource for quantum computation. Integrated CV quantum light sources offer a scalable pathway by harnessing low-loss nonlinear materials, versatile device architectures, and CMOS-compatible fabrication processes enabled by integrated photonics platforms. In this review, we briefly introduce recent progress on integrated CV quantum light sources, including single-mode squeezed states, two-mode squeezed states, and multimode entangled states. The key performance metrics of CV quantum light sources, such as the squeezing level, bandwidth, purity, and mode multiplexing, are analyzed. We highlight representative implementations of lithium niobate, silicon nitride, and silica platforms for CV quantum light sources and discuss major challenges for realizing integrated large-scale and fault-tolerant CV quantum computation.
Abstract Entanglement is an essential feature of quantum theory and the core of the majority of quantum information science and technologies. Quantum computing is one of the most important fruits of quantum entanglement and requires not only a bipartite entangled state but also more complicated multipartite entanglement. In previous experimental works to demonstrate various entanglement‐based quantum information processing, light has been extensively used. Experiments utilizing such a complicated state need highly complex optical circuits to propagate optical beams and a high level of spatial interference between different light beams to generate quantum entanglement or to efficiently perform balanced homodyne measurement. Current experiments have been performed in conventional free‐space optics with large numbers of optical components and a relatively large‐sized optical setup. Therefore, they are limited in stability and scalability. Integrated photonics offer new tools and additional capabilities for manipulating light in quantum information technology. Owing to integrated waveguide circuits, it is possible to stabilize and miniaturize complex optical circuits and achieve high interference of light beams. The integrated circuits have been firstly developed for discrete‐variable systems and then applied to continuous‐variable systems. In this article, we review the currently developed scheme for generation and verification of continuous‐variable quantum entanglement such as Einstein‐Podolsky‐Rosen beams using a photonic chip where waveguide circuits are integrated. This includes balanced homodyne measurement of a squeezed state of light. As a simple example, we also review an experiment for generating discrete‐variable quantum entanglement using integrated waveguide circuits.
Continuous-variable (CV) quantum microcombs generated in high-Q microresonators provide compact, frequency-multiplexed sources of entangled modes for integrated quantum information processing. Although deterministic Kerr-induced two-mode squeezing has been demonstrated on chip, achieving uniform squeezing across a large number of mode pairs remains a central challenge. Here we establish the conditions required for spectrally uniform squeezing and experimentally realize a vacuum-state CV quantum microcomb by combining a microresonator with an engineered single-family mode structure and optimized pump conditions. The device generates 14 independent two-mode squeezed states over a 0.7 THz bandwidth, each exhibiting more than 4 dB of raw squeezing, with a maximum of 4.3 dB. This uniform, high-performance quantum resource represents a key step toward scalable, integrated CV quantum technologies operating beyond classical limits.