Chang-Ling Zou

Fully connected quantum networks enable simultaneous connection of every user to every other user and are a highly versatile and robust networking architecture. However, the scalability of such networks remains a great challenge for practical applications. Here we construct a large-scale fully connected quantum network founded on two-photon Hong-Ou-Mandel (HOM) interference, where user-to-user security is guaranteed even with an untrusted network provider. Using integrated soliton microcomb (SMC) and photonic encoding chips, we realize precise, massively parallel frequency generation and locking, high-visibility HOM interference and measurement-device-independent (MDI) quantum key distribution. The proposed architecture enables a fully connected quantum network over 200 kilometers with strict information-theoretic security via an untrusted network provider. The implemented networking architecture paves the way for large-scale fully connected MDI quantum networks across metropolitan and intercity regions.

Optical microcavities, which exhibit ultrahigh quality factors and exceptional light-field confinement, have become an important platform for investigating nonlinear phenomena and developing highly sensitive sensors. Within these systems, photothermal oscillations induced by competing thermo-optic effects in multimaterial structures show considerable application potential. However, their practical implementation is severely limited by frequency drift and high phase noise. In this study, we demonstrate the first successful frequency stabilization of photothermal oscillation signals using electro-optic injection locking within an optofluidic microbubble resonator. Experimental results show that after locking, the linewidth of the frequency spectrum narrows markedly and the phase noise is reduced by more than 10 dB at an offset frequency of 10 Hz. Statistical analysis of 450 consecutive measurements reveals that the standard deviations of both the center frequency and peak power in the locked state are significantly lower than those in the unlocked state. This approach converts unstable photothermal oscillation signals into controlled outputs with narrow spectral bandwidth and improved phase stability. It, therefore, offers a promising strategy for overcoming signal instability, while preserving the ultrahigh sensitivity of microcavities, and provides a strong foundation for sensing applications such as biomolecule detection and environmental gas monitoring.

Current commercial optical isolators (OIs) primarily rely on the Faraday effect in magneto-optical materials, which necessitates the use of external magnetic fields. Here, we report a passive OI constructed from compact, commercially available optical components and an atomic vapor cell, which does not require a biasing magnetic field or any external drive, and only requires that the intensity of the forward beam is higher than that of the backward beam, which is very easy to satisfy in isolator applications. Operating at 795 nm, this device uses the principle of nonlinear non-reciprocity to achieve a bandwidth of 6 GHz and an isolation ratio greater than 30 dB.

High-fidelity two-logical-qubit gates are essential for realizing fault-tolerant quantum computation with bosonic codes, yet experimentally reported fidelities have rarely exceeded 90%. Here, we propose a geometric phase engineering approach for implementing controlled-phase gates for binomially encoded logical qubits. This method leverages the structural simplicity of geometric drives to reduce the numerical optimization dimensionality while fully incorporating system nonlinearities, enabling fast and high-fidelity logical operations. As an example, we experimentally demonstrate a process fidelity of 97.4±0.8% with postselection to exclude leakage (94.9±0.7% without post selection) for a controlled-Z gate between two lowest-order binomial codes, surpassing all previously reported two-logical-qubit gates in bosonic codes. This Letter demonstrates that geometric phase engineering provides an effective and experimentally feasible route to fast, high-fidelity logical operations in bosonic quantum processors.