A Hong, Ou, Mandel (HOM) interference visibility of nine hundred and ninety-two point zero plus or minus eight tenths of one percent has been achieved at the University of Science and Technology of China and collaborating institutions. Conventional methods predicted near-zero visibility for photons generated using continuous-wave driven microresonators due to limitations imposed by the joint spectral amplitude; however, finite-time detection combined with cavity-enhanced spontaneous four-wave mixing overcomes these bounds. The team establishes a new approach to generating identical photons suitable for quantum communication networks by optimising detector configuration.

The team overcame limitations previously thought inherent in using standard continuous wave lasers and compact silicon chips to create photon pairs; conventional understanding suggested near-zero performance due to restrictions on their combined spectral properties. This result challenges previous assumptions about photon generation using standard silicon chips and continuous wave lasers.

Perfect HOM interference, analogous to throwing two balls at the same hole where both might bounce back, indicates identical photons. Traditionally, limitations on a property called the joint spectral amplitude prevented high performance from these systems. The team overcomes these hurdles through finite-time detection combined with cavity-enhanced spontaneous four-wave mixing, which amplifies faint signals.

High Visibility Hong, Ou, Mandel Interference Using Finite-Time Detection and Silicon Nitride

Researchers surpass Hong, Ou, Mandel interference visibilities of 0.992 ±0.008, exceeding a long-standing limitation in quantum photon sources. This breakthrough demonstrates a sharp improvement over previous methods; those were restricted to values near zero when using continuous wave lasers and integrated microresonators. This crosses a key threshold previously thought impossible because conventional theory predicted low visibility due to restrictions on the spectral properties, the combined ‘colour’ characteristics, of generated photons.

Detector settings play an important role in improving heralded state qualities without complex filtering techniques by combining finite-time detection with cavity-enhanced spontaneous four-wave mixing within silicon nitride microresonators. A detector-conditioned heralded state governed by the detected idler photon’s window allows both indistinguishability of photons and heralding efficiency to approach unity, eliminating the need for complex spectral filters or source engineering. With fourfold count rates reaching 12.2 ±0.6Hz, achieving Hong, Ou, Mandel interference visibilities of 0.942 ±0.012 was possible; this indicates strong performance even when many photon pairs are generated per second.

High-Q silicon nitride microresonators were used in these experiments which enhance light confinement within tiny structures, exhibiting quality factors exceeding expectations for CW pumping schemes. The team simulated a pulsed pump driving their microresonator system, attaining a joint spectral amplitude-derived purity of 0.92 and demonstrating that this approach sharply improves spectral characteristics compared to continuous wave methods alone.

This technique is akin to listening for an echo within a specific time window after making a sound, addressing limitations inherent in generating identical photon pairs using continuous wave lasers and compact silicon chips; conventional methods struggle with the precision of colour or frequency content, known as spectral purity. By carefully controlling detector ‘listening windows’, they optimise both photon similarity and heralding event detection efficiency without complex filtering systems, fabricating integrated silicon nitride microresonators which generate paired photons via cavity-enhanced spontaneous four-wave mixing supporting high quality factor resonances enhancing faint signals.

Compact silicon chips generate high fidelity photons for quantum networks

Creating dependable sources of identical photons is essential for scalable quantum networks, underpinning tasks like secure communication and distributed computation. Researchers demonstrate a pathway to high-quality photon pairs using compact silicon chips and continuous wave lasers; this seemingly simple approach defied conventional wisdom predicting poor performance based solely on the spectral properties of generated light. Simulations also reveal potential gains from switching to pulsed laser excitation, achieving even greater control over these same characteristics.

Acknowledging concerns about assessing true photon indistinguishability, where subtle spectral features can mask genuine performance, this demonstration remains significant as it validates a readily scalable approach to building quantum devices utilising existing silicon chip technology and continuous wave lasers. The team achieves near-unity Hong, Ou, Mandel interference visibility, challenging the understanding that photon pair sources are limited by their joint spectral amplitude and establishing detector configuration as key for high-quality heralded states.

The research demonstrated high fidelity paired photons using continuously driven silicon nitride microresonators. This matters because dependable single-photon sources are a fundamental requirement for building practical quantum networks capable of secure communication and distributed computation. By optimising detector settings alongside cavity-enhanced spontaneous four-wave mixing, researchers achieved Hong, Ou, Mandel interference visibilities of 0.992 ±0.008 and 0.942 ±0.012 at count rates up to 12.2Hz. The authors suggest exploring pulsed laser excitation as a potential route towards further improvements in photon characteristics.

👉 More information
🗞 Filter-Free Indistinguishable Photon Generation from Continuous-Wave-Driven Integrated Microresonators
✍️ Ruiyang Chen, Sicheng Zeng, Yuan Chen, Sanli Huang, Zeying Zhong, Zhen Chen, Xue Bai, Yi-Han Luo and Junqiu Liu
🧠 ArXiv: https://arxiv.org/abs/2609.18575

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