专题 · 量子密码、量子纠缠、集成光子学与光纤传感

Large-scale quantum networks will enable entirely new applications of quantum information science in fields such as quantum communication, distributed quantum computing, sensing, and metrology. To build nodes of such networks, diamond color defects are one of the promising candidates. Their excellent optical properties, fast spin-qubit control, and long spin coherence times make them well suited for quantum information processing and quantum memory applications. Additionally, recent advances in the heterogeneous integration of diamond nanophotonic structures with photonic integrated circuits have made these systems more efficient and well suited for scalable quantum processor architectures. In this comprehensive review, we discuss the optical and spin properties of these systems, recent progress in the building blocks of quantum networks, and demonstrations of metropolitan-scale quantum networks, as well as the challenges associated with these systems at both the fundamental and experimental levels, along with potential solutions.

Deterministic remote entanglement of superconducting qutrits via time-bin microwave photons surpasses the negativity bound of two-qubit states.

Spectral crowding of collective motional modes limits the fidelity of entangling interactions in trapped-ion quantum processors by inducing off-resonant coupling to spectator modes. We introduce a geometric-phase entangling interaction driven by a transverse, time-dependent structured-light force. By applying the force in a plane orthogonal to the optical propagation direction, we reduce the effects of spectral crowding while preserving single-ion addressing. The scheme is compatible with arbitrary qubit encodings, provided that the qubit states experience a differential AC Stark shift. We experimentally realize high-fidelity two-qubit gates with error rates below 5 × 10 − 3 in ion crystals containing up to 12 ions confined within a single potential well. These results establish gradient-field light-shift gates as a scalable approach to high-fidelity entanglement generation in spectrally crowded trapped-ion systems.

We show that a bound impurity in a Bose-Einstein condensate can be directly mapped to an Unruh-DeWitt detector interacting with a relativistic quantum field. We provide explicit experimental parameters for an implementation using K 41 impurities coupled to a Rb 87 condensate via finite-time Feshbach tuning. As an application, we study the extraction of vacuum entanglement from distant regions of the condensate and find viable parameters for the implementation of entanglement harvesting.

Modern precision experiments often probe unknown classical fields with bosonic sensors in quantum-noise-limited regimes where vacuum fluctuations limit conventional readout. We introduce quantum signal learning, a sensing framework that extends metrology to a broader property-learning setting, and propose a quantum-enhanced protocol that simultaneously estimates many properties of a classical signal with shot noise suppressed below the vacuum level. Our scheme requires only two-mode squeezing, passive optics, and static homodyne measurements, and enables post hoc classical estimation of many properties from the same experimental dataset. We prove that our protocol enables a quantum speedup for common classical sensing tasks, including measuring electromagnetic correlations, real-time feedback control of interferometric cavities, and Fourier-domain matched filtering. To establish these separations, we introduce an optimal-transport conditioning method and show both worst-case exponential separations from all entanglement-free strategies and practical speedups over homodyne and heterodyne baselines. We further show that when squeezing is treated as a resource, a protocol with squeezed light can sense a structured classical background exponentially faster than any coherent classical probe.

Entanglement is a central resource in quantum technologies, and the realization of photonic entanglement necessarily relies on interaction with matter. Resonance fluorescence, originating from the coherent interaction between a driving field and a two-level system, plays a pivotal role in quantum optics. Here, we experimentally demonstrate high-quality generation of post-selected temporal-mode entanglement using vacuum–one-photon number superposition states from a single quantum dot, an approach conceptually aligned with early proposals based on identical single photons, yet whose high-quality experimental realization has remained absent. By delocalizing this superposition via a beam splitter, we realize post-selected temporal-mode entanglement and observe a clear violation of the Clauser–Horn–Shimony–Holt Bell inequality using Franson-type interferometry. Our scheme removes the need for multiphoton generation, simplifies the experimental requirements, and establishes a scalable pathway toward solid-state entangled photon sources.

Silicon is a leading material platform for photonic quantum technologies. However, a key challenge remains the efficient integration of high-performance single-photon sources in the near infrared. Here we present an all-silicon single-photon source at 1217 nm wavelength, fabricated by nanoscale positioning of a single W center in a circular Bragg grating cavity. The operation wavelength corresponds to the W center’s zero-phonon line that is enhanced by the cavity. Under above-gap continuous-wave excitation, we obtain a saturated photon count rate of 1.29 × 10 6 counts/s with pronounced photon antibunching ( g (2) (0) = 0.06 ± 0.02). Triggered operation under weak pulsed excitation produces single photons with 93 ± 2% purity. At saturation, we reveal purity degradation due to repumping processes, that could be mitigated using selective excitation schemes in the future. These results represent a major step towards on-demand sources of indistinguishable single photons in silicon photonics.

Realizing photonic quantum computing at scale requires integrated circuits that combine ultra-low loss with fast, low-power, low-hysteresis, and low-crosstalk reconfiguration. These requirements are particularly challenging at visible wavelengths, where many quantum resource-state generators, including single-photon sources and quantum memories, naturally operate. Low-confinement silicon nitride waveguides offer the requisite loss performance, but conventional thermo-optic modulators dissipate significant static power, driving thermal crosstalk and precluding cryogenic operation. Visible-wavelength piezo-optomechanical circuits avoid these drawbacks, but existing demonstrations rely either on high-confinement waveguides with propagation losses of 35-100 dB/m, or on low-confinement platforms using foundry-incompatible lead zirconate titanate (PZT). Here we combine piezo-optomechanical actuation with a CMOS-foundry-fabricated, low-confinement silicon nitride platform, achieving 2.6 dB/m propagation loss at 780 nm, megahertz-scale modulation bandwidth, a half-wave voltage-length product of 2.8 V ⋅ m, and negligible hysteresis. We demonstrate reconfigurable Mach-Zehnder interferometers with 0.63 dB loss per spiral phase shifter, enabling deep, actively reconfigurable visible-wavelength quantum photonic circuits.

Non-Hermitian physics has unlocked a wealth of unconventional wave phenomena beyond the reach of Hermitian systems, with exceptional points (EPs) driving enhanced sensitivity, nonreciprocal transport, and topological behavior unique to non-Hermitian degeneracies. Here, we present a scalable and reconfigurable silicon photonic integrated circuit capable of emulating arbitrary non-Hermitian time evolution with high precision. Using this programmable platform, we implement a two-band non-Hermitian Hamiltonian defined on a Klein-bottle topology, a nonorientable parameter space that enables exceptional phases forbidden on orientable manifolds. Through an on-chip amplitude-and-phase reconstruction protocol, we retrieve the full complex Hamiltonian at multiple points in parameter space and experimentally map the associated Fermi arc where the imaginary eigenvalue gap closes. The orientation of the measured Fermi arc reveals a nontrivial exceptional topology: it implies the presence of same-charge EPs (or an EP monopole) that cannot annihilate locally on the Klein bottle. Our results demonstrate the first photonic realization of exceptional topology on a nonorientable manifold and establish a versatile platform for exploring exotic non-Hermitian and topological models relevant to classical and quantum photonics.

Large-scale quantum networks will enable entirely new applications of quantum information science in fields such as quantum communication, distributed quantum computing, sensing, and metrology. To build nodes of such networks, diamond color defects are one of the promising candidates. Their excellent optical properties, fast spin-qubit control, and long spin coherence times make them well suited for quantum information processing and quantum memory applications. Additionally, recent advances in the heterogeneous integration of diamond nanophotonic structures with photonic integrated circuits have made these systems more efficient and well suited for scalable quantum processor architectures. In this comprehensive review, we discuss the optical and spin properties of these systems, recent progress in the building blocks of quantum networks, and demonstrations of metropolitan-scale quantum networks, as well as the challenges associated with these systems at both the fundamental and experimental levels, along with potential solutions.

Synchronized laser oscillators are essential for probing the fastest processes in chemistry, materials science, and biology down to attosecond timescales. Tight synchronization is also crucial at scientific facilities such as free-electron lasers or radio telescopes and is increasingly relevant to communication and information technologies in multi-node networks. Current synchronization approaches based on mode-locked lasers achieve the required performance, but their complexity, cost, and size hinder deployment in multi-node networks. Here, we demonstrate attosecond-level synchronization between chip-integrated microresonator soliton combs operating at either 25 or 300 GHz pulse repetition rate. For synchronization, each oscillator receives over fiber a pair of continuous-wave lasers as a two-tone timing reference. The lasers power the microcombs, and Kerr-nonlinear synchronization results in integrated relative timing jitter below 400 as (1 kHz to 1 MHz), without any active stabilization. This approach enables scalable precision timing for large facilities, data centers, disaggregated computing, navigation, and quantum networks; ultimately, it may lead to chip-integrated attosecond photonics.

Optical modulators in the visible regime have far-reaching applications from biophotonics to quantum science. Implementations of such optical phase modulators on a silicon-on-insulator waveguide platform have been mainly limited to utilization of the thermo-optic effect, liquid crystal technology, as well as piezo-optomechanical effects which are limited in modulation speed and modulation efficiency. Here, we report, to our knowledge, the demonstration of the first highly scalable compact phase modulator in the visible regime based on altering the refractive index of an indium-tin oxide capacitive stack over a Si 3 N 4 waveguide through the charge accumulation effect. The phase modulator architecture achieves a modulation efficiency, V π L, of 0.5V⋅cm at a zero static power consumption. Bandwidth and V π scale inversely, with the minimum V π value being 12.4±0.4V for a 400 µm long modulator and a corresponding phase modulator loss of 2.5 dB, and the highest −3dB bandwidth being 150 MHz for a 10 µm long modulator with a corresponding phase modulator loss of 0.06 dB. By enhancing the energy efficiency and bandwidth of phase modulators in the visible regime, this work enables implementation of large-scale and high-speed integrated photonic systems with applications from biotechnology to quantum sensing and computing.