Researchers in China have achieved a major leap in quantum photonics by generating a massive 60-mode entangled cluster state directly on a chip using optical microresonators.
By leveraging a deterministic, continuous-variable approach and a multiple-laser pump technique, they overcame traditional limitations in scalability. The team confirmed high-quality entanglement using advanced detection methods, paving the way for powerful quantum technologies like chip-based computers, secure communications, and cutting-edge sensors.
Breakthrough in On-Chip Quantum Entanglement
A research team from Peking University and the Chinese Academy of Sciences has achieved a major advance in quantum photonics by generating large-scale entangled states—known as cluster states—directly on a chip. Using optical microresonators, they produced a 60-mode cluster state, which is about ten times larger than what had been previously achieved with on-chip systems. Their findings were published in Light: Science & Applications.
Cluster states are crucial for many quantum technologies because they allow multiple quantum systems to interact in a coordinated, entangled way. This kind of entanglement underpins powerful applications in quantum computing, ultra-secure communications, and precision sensing. Until now, creating large cluster states on a chip was challenging, as most methods relied on probabilistic processes that limited scalability. The researchers overcame this by using a continuous-variable approach that generates entanglement deterministically—meaning reliably and on demand.
How Optical Microresonators Enable Scalable Entanglement
At the heart of the breakthrough is an optical microresonator, a tiny ring-shaped device that traps light in a circular path and supports a series of closely spaced frequency modes. The team used up to three synchronized lasers in a multi-pump setup. The main laser triggered degenerate four-wave mixing to produce pairs of entangled light modes, while the other lasers added additional connections through non-degenerate four-wave mixing. Together, this setup created a highly interconnected network of 60 entangled light modes, arranged in both linear and grid-like structures.
Advanced measurement techniques, including phase-locked balanced homodyne detection, were used to directly assess the orthogonal quadratures of the light modes. By constructing a covariance matrix and applying the positive partial transpose (PPT) criterion, the researchers confirmed the stability of the entanglement links, with a measured squeezing of up to 3 dB—a world-leading squeezing level clearly indicating high-quality entanglement.
Toward Scalable, Practical Quantum Devices
This achievement not only provides a robust experimental platform for exploring quantum entanglement but also paves the way for the development of scalable, chip-based quantum light sources. They could be the foundation for next-generation quantum computers, ultra-secure communications, and advanced sensors, all within compact and efficient devices.
Reference: “Large-scale cluster quantum microcombs” by Ze Wang, Kangkang Li, Yue Wang, Xin Zhou, Yinke Cheng, Boxuan Jing, Fengxiao Sun, Jincheng Li, Zhilin Li, Bingyan Wu, Qihuang Gong, Qiongyi He, Bei-Bei Li and Qi-Fan Yang, 16 April 2025, Light: Science & Applications.
DOI: 10.1038/s41377-025-01812-2
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