High-performance photonic chips provide a powerful platform for analog computing, enabling the simulation of high-dimensional physical systems using low-dimensional devices with additional synthetic dimensions. The realization of large-scale complex simulations necessitates an architecture capable of rich coupling configurations (encompassing symmetric, asymmetric and long-range coupling schemes) which is also crucial for scaling up. Previous approaches rely on excessive physical components to introduce asymmetric coupling, however, are restricted in reconfiguring and scaling by the relatively complicated structures. Here, to solve this problem, we propose a hybrid-frequency synthetic-dimension simulator architecture that combines both intra-resonant and inter-resonant frequency-lattice sites, and experimentally demonstrate it using the thin-film lithium niobate (TFLN) photonic chip. Employing this hybrid programmable architecture, we are able to simulate both the regular and long-range coupled forms of diverse compound-lattice models, such as the Hall ladder, Creutz ladder (symmetric) and Su-Schrieffer-Heeger (SSH, asymmetric) model, on a single chip, simultaneously reducing the experimental requirements significantly. As results, the direct readout of the bandstructure of the SSH model is able to be achieved, to be distinguished from all previous works, and important phenomena such as spin-momentum locking, topological flat band and Aharonov-Bohm cage effect are also observed with lower experimental requirements. Furthermore, applications like piecewise-continuous optical frequency shifting can be enabled by cascading our devices. Our results offer promising insights for future large-scale complex on-chip simulators with rich couplings.

Photons are essential for interconnecting quantum systems in quantum networks, where polarization is a widely used degree of freedom for encoding quantum information. However, frequency bands suitable for different quantum systems often do not align. While polarization-preserving quantum frequency conversion (PPQFC) is essential for interconnecting heterogeneous quantum systems, existing solutions lack cross-band capability between ultraviolet (UV) and near-infrared (NIR) regimes. Here, we experimentally demonstrated a PPQFC method that exploits the low-loss, self-phase stabilization of polarization and facilitates cross-band achromatic waveguide coupling. Specifically, we demonstrated the polarization-preserving quantum frequency conversion from UV 369.5 nm to visible 580 nm with infrared pumping at 1018 nm, achieving long-term fidelity of 97.6% +/- 1.0% at wavelengths relevant to trapped ions 171Yb+ and solid-state 153Eu3+:Y2SiO5 quantum systems. This work demonstrates a versatile PPQFC solution for future heterogeneous quantum networks.

Quantum mechanics is compatible with scenarios where physical processes happen in an indefinite order. In theory, this feature could be detected through violations of inequalities on the observed correlations, analogous to Bell inequalities. However, experimental demonstrations of such violations have been missing until recently due to the complexity of the required setup. Here, we report an experimental violation of a Bell-like inequality involving the correlations of four parties, one of which is spacelike separated from the others. Our demonstration uses 3-kilometer fiber spools to simulate spacelike separation and achieves high-speed operations in photonic time-bin encoding, nanosecond synchronization, and accurate temperature stabilization. These experimental advances enable a violation by 5.7 SDs and open a path toward a certification of indefinite order in conditions that guarantee spacelike separation with existing state-of-the-art devices. However, the certification is not device independent, as it relies on knowledge about the setup to exclude bidirectional signaling-a loophole inherent to implementations in classical acyclic spacetimes, which may be resolved in future quantum-spacetime tests.

We investigate quantum quenches starting from a critical point and experimentally probe the associated defect statistics using a trapped-ion quantum simulator of the transverse-field Ising model. The cumulants of the defect number distribution exhibit universal scaling with quench depth, featuring Gaussian behavior at leading order and systematic subleading corrections. Our results are in excellent agreement with both exact and approximate theoretical predictions, establishing quench-depth scaling as a powerful and precise experimental benchmark for nonequilibrium quantum critical dynamics.

Modified divacancies in the 4H polytype of silicon carbide (SiC) exhibit enhanced charge stability and spin addressability at room temperature, making them attractive for quantum applications. However, their low formation yield and lack of direct structural identification have hindered progress. Here, we demonstrate a controllable method for high-yield engineering and identification of oxygen-related modified divacancy color centers in 4H-SiC via oxygen-ion implantation. Based on their distinct optical and spin-resonance characteristics, we experimentally resolve four types of modified divacancies. Furthermore, by measuring isotope-resolved 17 O $^{17}{\rm O}$ hyperfine interactions, we identify them as the four crystallographic configurations of oxygen-vacancy (OV) complexes. Remarkably, single OV centers account for over 90% of the total defect population and exhibit superior optical properties and spin coherence compared with defects created by conventional carbon or nitrogen implantation. We characterize the zero-phonon lines of these OV centers and reveal distinct temperature-dependent behavior in spin-readout contrast. By optimizing implantation dose and annealing temperature, we achieve high-density ensembles and observe Rabi-oscillation beating patterns associated with different orientations of basal-type defects. These results establish a high-yield route for scalable engineering of these four oxygen-related modified divacancies in 4H-SiC and clarify their atomic structure, opening new opportunities for solid-state quantum technologies.

Weak measurement (WM) offers the advantage of amplifying small signals at the cost of postselecting a small portion of the probes. This so-called weak-value amplification effect makes it compare favorably with conventional techniques (without postselection) to overcome various technical noises. However, certain types of technical noise, such as jitter and pixelation, present insurmountable limitations for both WM and conventional techniques. In this work, we propose an advanced variant of WM that incorporates time-momentum correlation (TMC) into biased weak measurement (BWM). By employing the Fisher information metric, we theoretically show that TMC-BWM can overcome jitter and pixelation, and meanwhile extract significantly higher Fisher information. This dual advantage was experimentally validated in a magnetic-sensing application when applying severe jitter and pixelation, and it remains robust under natural conditions, achieving a 24.8-dB improvement in precision over the standard WM scheme. Moreover, merely classical resources are required to achieve this dual metrological advantage.

Observation of the universe demands telescopes with high resolution. In the optical band, traditional interference requires bringing interfering fields together, which limits the resolution due to the restricted length of baseline. Here we demonstrate the very long-baseline interferometer (VLBI) in optical band, where two interfering fields never met each other. In particular, we report the first quantum interference observation when the input of VLBI is single-photon state. Interference is recovered after measuring the amplitudes of photon fields and digitally processing the signals of quantum receivers. Moreover, we analyze interference in time and spectral domains for broadband thermal light input and show that the ultrahigh spectral resolution can improve the precision of radial velocity to 0.08 centimeters per second, which is 2 orders of magnitude better than that achievable at the current stage. Further, we apply the spectrally resolved interference in distinguishing two independent sources with angular resolutions beyond diffraction limit. Our investigations have a profound effect on the VLBI, quantum optics, and precision measurement.

Solid-state spin defects encode local perturbations as measurable shifts in spin-transition frequencies, but mechanical actuation and quantum readout remain physically separated, resulting in a discrete measurement setup. Integrating these functions requires an on-site mechano-quantum interface that programs the lattice state of a defect host and quantitatively maps it onto the spin Hamiltonian. Here we first report an on-chip programmable mechano-quantum transducer (OCPMQT) that integrates voltage-defined micromechanical actuation with in situ spin-frequency readout in a two-dimensional van der Waals quantum-defect host. Mechanically programmed lattice states are encoded as shifts in the axial zero-field splitting parameter and resolved by optically detected magnetic resonance (ODMR) spectroscopy. Within a chip volume of 2.05*10^-2 cm^3, the transducer accesses ODMR-inferred strains as low as 0.0080

Photons are among the most important carriers of quantum information owing to their rich degrees of freedom (DoFs), including various spatiotemporal structures. The ability to characterize these DoFs, as well as the hidden correlations among them, directly determines whether they can be exploited for quantum tasks. While various methods have been developed for measuring the spatiotemporal structure of classical light fields, owing to the technical challenges posed by weak photon flux, there have so far been no reports of observing such structures in their quantum counterparts, except for a few studies limited to correlations within individual DoFs. Here, we propose and experimentally demonstrate a self-referenced, high-efficiency, and all-optical method, termed 3D imaging of photonic wave packets, for comprehensive characterization of the spatiotemporal structure of a quantum light field, i.e., the biphoton spatiotemporal wave packet. Benefiting from this developed method, we successfully observe the spatial-spatial, spectral-spectral, and spatiotemporal correlations of biphotons generated via spontaneous parametric down-conversion, revealing rich local and nonlocal spatiotemporal structure in quantum light fields. This method will further advance the understanding of the dynamics in nonlinear quantum optics and expand the potential of photons for applications in quantum communication and quantum computing.

Solid-state color centers are promising candidates for nodes in quantum network architectures. However, realizing scalable and fully functional quantum nodes, comprising both processor and memory qubits with high-fidelity universal gate operations, remains a central challenge in this field. Here, we demonstrate a fully functional quantum node in silicon carbide, where electron spins act as quantum processors and nuclear spins serve as quantum memory. Specifically, we design a pulse sequence that combines dynamical decoupling with hyperfine interactions to realize decoherence-protected universal gate operations between the processor and memory qubits. Leveraging this gate, we deterministically prepare entangled states within the quantum node, achieving a fidelity of 90

The negatively charged boron vacancy in two-dimensional hexagonal boron nitride has emerged as a promising candidate for quantum sensing. The coherence time of this defect spins which coherent quantum sensing resides in is limited spin-phonon interactions, while the underlying physical mechanism of the corresponding high-temperature behavior is still not fully understood. Here, we probe the single- and double-quantum relaxation rates on this center over the temperature range from 293 to 393 K. The results show that both relaxation rates increase with increasing temperature, and the double-quantum relaxation rate significantly increases rapidly. At high temperature (above 400 K), the double-quantum relaxation rate is much greater than single-quantum relaxation rate, and may dominate the decoherence channel of spin-phonon interactions. Using a theoretical model of second-order spin-phonon interactions, we attribute the high-temperature spin relaxation rates to interactions with higher-energy effective phonon mode, aiding the further understanding and guiding high-temperature sensing applications.

Quantum systems can be fundamentally classified into discrete-variable (DV) and continuous-variable (CV) systems. The degree of quantum advantage achieved with a quantum system is often dictated by the scalability, robustness, and operational feasibility-factors that are closely tied to the nature of the variables employed. Notably, DV and CV systems are largely complementary in these factors. Consequently, integrating DV and CV variables holds significant promise for overcoming the inherent challenges associated with relying solely on one type of variable system. In this study, we build a bidirectional quantum analog-to-digital converter (QADC/QDAC), which facilitates deterministic and reversible quantum information transfer between CV and DV systems. This QADC/QDAC is hardware-efficient, and the error decreases exponentially with the number of qubits, thereby allowing high-fidelity information transfer with a few qubits. With this photonic QADC/QDAC, we demonstrate efficient CV mode tomography leveraging DV tomography techniques and achieve deterministic generation of non-Gaussian CV mode from qubits. Our findings address a critical barrier in constructing hybrid quantum processors and open up new avenues for scientific exploration previously inaccessible to single-variable quantum systems.

Open systems feature a variety of phenomena that arise from non-Hermitian physics. Recent theoretical studies have offered many insights into these phenomena through the non-Bloch band theory, though many of the theory's key features are experimentally elusive. In particular, the correspondence between complex momenta and non-Hermitian bands, while central to non-Bloch band theory, has so far defied direct experimental observation. Here we experimentally study the non-Hermitian spectral deformation in complex-momentum space, by implementing a non-Hermitian lattice with long-range couplings in the synthetic orbital-angular-momentum (OAM) dimension of photons inside a degenerate cavity. Encoding the complex momenta in the phase and amplitude modulations of the OAM modes, and devising a complex-momentum-resolved projective detection, we reconstruct the spectral deformation in complex-momentum space, where the eigenspectrum on the complex plane morphs through distinct geometries. This enables us to experimentally extract key information of the system under the non-Bloch band theory, including exceptional points in the complex-momentum space, the open-boundary spectra, and the generalized Brillouin zone. Our work demonstrates a versatile platform for exploring non-Hermitian physics and non-Bloch band theory, and opens the avenue for direct experimental investigation of non-Bloch features in the complex-momentum space.

High-fidelity focused spots, achieving the diffraction limit and ultra-low crosstalk, are critical for manipulating trapped atoms and ions. Despite the existence of various aberration compensation techniques, obtaining such high-quality focused spots remains challenging for far-detuned laser systems. Here, we demonstrate a universal in-situ aberration correction technique for far-detuned-laser-based individual addressing systems. Our approach utilizes a trapped ion as a probe and a spatial light modulator for optical aberration compensation, demonstrating 17-fold suppression of crosstalk and achieving a low Rabi crosstalk of 0.031(4)%, nearly a four-fold improvement over previous state-of-the-art results. This method establishes an effective tool for high-fidelity quantum operations in trapped ion and atom systems, pivotal for quantum computing.

In the last decade, it was understood that quantum networks involving several independent sources of entanglement which are distributed and measured by several parties allowed for completely novel forms of nonclassical quantum correlations, when entangled measurements are performed. Here, we experimentally obtain quantum correlations in a triangle network structure, and provide solid evidence of its nonlocality. Specifically, we first obtain the elegant distribution proposed in (Entropy 21, 325) by performing a six-photon experiment. Then, we justify its nonlocality based on machine learning tools to estimate the distance of the experimentally obtained correlation to the local set, and through the violation of a family of conjectured inequalities tailored for the triangle network.

Global-scale entanglement distribution has been a formidable challenge due to the unavoidable losses in communication channels. Here we propose a backbone channel for a quantum network based on balloon-based aerial relays. We demonstrate that the atmospheric disturbances in balloon-based channels can be almost eliminated through optimizing beam waist positions and employing a series of adaptive optics systems, which boosts the channel efficiency to -21 dB over a 10 000 km distance, outperforming satellite-based relays by 12 dB with the same device parameters. We then propose a global-scale quantum networking scheme based on hybrid-channel quantum repeaters that combine ground-based quantum repeaters and balloon-based aerial relays. Servers are interconnected globally via a chain of balloons, while multiple clients link to local servers through fiber connections, facilitating rapid client switching and network scalability. Our simulations, employing stateof-the-art Eu3+:Y2SiO5 quantum memories and mature entanglement sources based on spontaneous parametric down-conversion, demonstrate an entanglement distribution rate in the subhertz range between clients separated by 10 000 km. This approach offers a practical path toward global quantum networking in the near future.

Entanglement is fundamental to quantum physics and information processing. In this work, we introduce the Few-Shot Randomized Measurement (FSRM) method, developing an unbiased estimator for mixed-state entanglement from just three experimental shot outcomes. By incorporating the Bell measurement (BM), we supplement the traditional computational-basis measurement to enhance the randomized measurement scheme, which is scalable to n-qubit systems via BMs on qubit pairs. Our approach enables direct estimation of entanglement through random unitary evolution in a photonic system. Compared to the classical shadow method, BM-enhanced FSRM requires no prior knowledge of the local unitaries, offering greater robustness against unitary imperfections. Additionally, we find that utilizing more versatile measurement settings with fewer repeats per setting is more efficient under fixed measurement resources. Our protocol and experimental demonstration represent a significant advancement in the efficient and practical characterization of quantum states.

Gaussian boson sampling (GBS) provides a route toward demonstrating quantum computational advantage. However, optical loss, which reduces the entanglement in the system, can render GBS results classically simulable. We propose a nonlinear photonic architecture based on optical parametric amplifiers (OPAs) arranged in an interferometer network. This active configuration amplifies quantum correlations within the circuit while preserving the #P-hard Hafnian structure of the output probabilities. Using logarithmic negativity, we numerically show that entanglement scales linearly with both the OPA gain and network depth in the lossless limit and maintains linear scaling with the number of modes under realistic loss rate. These scaling behaviors suggest that classical simulation in lossy scenarios remains computationally intractable. The decomposition of the output into a core state and a random Gaussian displacement shows that the SU(1,1) network outperforms the SU(2) network when loss is present. Our results demonstrate that OPA-boosted GBS preserves computational hardness in noisy environments, offering a more effective implementations of near-term photonic quantum computers.

Quantum sensor networks typically encode N unknown parameters while targeting a single linear combination, rendering the N-1 remaining parameters as nuisance directions. To rigorously quantify estimation precision under such nuisances, we introduce the concept of effective quantum Fisher information (EQFI) and develop an exact EQFI-based phase map that systematically describes the allocation between local and global EQFI. Leveraging this geometric framework, we identify a fundamental bottleneck termed the "barrel effect": the global EQFI is strictly bounded by the weakest weighted local sensing capacity among all nodes. We further establish concrete conditions for saturating this bound. Crucially, this geometric map delineates how the trade-off between local and global EQFI depends dynamically on quantum correlations, and uncovers a counterintuitive "overcorrelated" regime where excessive correlations actively degrade both local and global performance. Finally, we apply the phase map to intrinsic local privacy and identify the condition under which every local parameter is inaccessible while the desired global combination remains estimable. Overall, our work provides a principled methodology for engineering optimal network states in quantum sensing architectures.