Quantum secure direct communication (QSDC), a paradigm-shifting breakthrough in quantum communication, exploits quantum states for unmediated information transmission. Rooted in the inviolable fundamental laws of quantum mechanics, QSDC enables ultrasensitive detection of even the faintest eavesdropping attempts, guaranteeing true communication security solely when no interference exists. However, its practical scalability remains constrained by insufficient transmission rates. Semantic communication, which drastically boosts transmission efficiency by extracting core information features, nevertheless stays vulnerable to malicious intrusions. Integrating these paradigms promises to simultaneously enhance the equivalent data rate and security. Herein, we propose and experimentally validate a quantum semantic communication scheme, applying it to 3-dimensional point clouds. It achieves a 46.30-fold efficiency gain over direct transmission in the meaning domain, beyond the Wyner and Shannon capacity limits of syntactic communication. This breakthrough not only broadens the application scope of QSDC with limited bandwidth, but also marks a pivotal milestone in quantum information science.

Quantum Key Distribution (QKD) represents a groundbreaking cryptographic technology that enables theoretically unconditionally secure key generation between communication parties. With recent advancements in network integration, QKD systems have been successfully deployed across diverse complex scenarios. For last-mile access network applications, free-space optical channels emerge as an optimal transmission medium. In this work, we implement a free-space QKD system employing a high-repetition-rate phase-encoding BB84 protocol. The experimental setup incorporates a simplified, highly integrable synchronization apparatus and self-compensating phase drift correction mechanism, which enhances both system stability and secure key generation rate. Experimental results demonstrate robust performance over a 1.4-km free-space channel with approximately 13 dB attenuation, achieving a secure key rate (SKR) of 160.19 kbps while maintaining a quantum bit error rate (QBER) of 2.3%. These findings establish the feasibility and efficiency of phase-encoded free-space QKD for last-mile access network applications. 2026 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

Recent studies have revealed reentrant-localization transitions in quasiperiodic one-dimensional lattices, where the competition between dimerized hopping and staggered disorder plays a central role. However, it remains unclear under what conditions reentrant localization and, in particular, multiple reentrant localization can occur. Here we investigate localization phenomena in a one-dimensional lattice subject to a periodic potential and an additional quasiperiodic modulation. Using both eigenstate-resolved indicators and experimentally accessible dynamical observables, we identify robust multiple-reentrant-localization transitions. We show that these transitions are uniquely stabilized by the dimer structure of the unit cell, where the competition between the on-site periodic potential and the quasiperiodic modulation becomes most pronounced. By systematically varying the periodicity parameter alpha and the quasiperiodic frequency beta, we find that the robust multiple-reentrant-localization behavior disappears for any deviation from the dimer configuration, confirming its essential role. Our results suggest that the interplay between these competing factors drives the multiple-reentrant-localization transitions.

Robust quantum transmission is driving a new paradigm in space-ground quantum networking. Although phase encoding has been widely adopted in terrestrial fiber channels, it has long been considered unsuitable for free-space quantum communication. Here, we demonstrate phase-encoded quantum communication over 1400 m of urban free space. The system maintained stable operation for nearly one hour, achieving 99.07

Quantum communication has reached a rate bottleneck, yet enhancing its throughput remains of profound significance. Here, we propose a scheme termed semantic quantum secure direct communication (QSDC), which is a novel paradigm integrating semantic communication with QSDC to realize highly efficient, task-oriented, and intrinsically secure information transmission. In semantic QSDC, meaningful semantic content is directly encoded into quantum states, whereby the fundamental laws of quantum physics guarantee inherent eavesdropping-detection capability and information-theoretic security. By harnessing semantic compression and artificial intelligence–assisted encoding strategies, this approach surpasses the intrinsic rate constraints of conventional QSDC. Simulation results show that semantic QSDC can surpass the Shannonian mutual information bound compared with conventional QSDC systems and demonstrate its potential to break through the linear rate-transmittance bound of quantum communication. These findings pave the way for high-rate secure communication.

The Riemann Hypothesis (RH), one of the most profound unsolved problems in mathematics, concerns the nontrivial zeros of the Riemann zeta function. Establishing connections between the RH and physical phenomena could offer new perspectives on its physical origin and verification. Here, we establish a direct correspondence between the nontrivial zeros of the zeta function and dynamical quantum phase transitions (DQPTs) in two realizable quantum systems, characterized by the averaged accumulated phase factor and the Loschmidt amplitude, respectively. This precise correspondence reveals that the RH can be viewed as the emergence of DQPTs at a specific temperature. We experimentally demonstrate this correspondence on a five-qubit spin-based system and further propose an universal quantum simulation framework for efficiently realizing both systems with polynomial resources, offering a quantum advantage for numerical verification of the RH. These findings uncover an intrinsic link between nonequilibrium critical dynamics and the RH, positioning quantum computing as a powerful platform for exploring one of mathematics' most enduring conjectures and beyond.

We present an analytical solution for the complex spectrum of a Creutz ladder subject to an imaginary Stark potential. By mapping the system to a momentum-space differential equation, we derive the closed-form solution for the momentum-space wavefunctions. We identify a distinct cross-shaped spectrum consisting of discrete localized sectors and a continuous branch of asymptotically real states. Our derivation reveals that the discrete sectors arise from a global phase winding condition, whereas the asymptotically real branch emerges when the energy magnitude is smaller than the inter-cell hopping strength, a regime in which the momentum-space wavefunction develops singularities. We demonstrate that these singularities prevent standard quantization; instead, the open boundary conditions are satisfied via a size-dependent imaginary energy component that regulates the wavefunction decay. To investigate the properties of this branch in the thermodynamic limit, we perform large-scale finite-size scaling analysis up to system sizes L∼109. The numerical results confirm the power-law decay of the residual imaginary energy, supporting the asymptotic reality of these states. Furthermore, scaling of the inverse participation ratio and fractal dimension indicates that these states, while exhibiting size-dependent localization in finite systems, evolve into an extended phase in the thermodynamic limit. Our results establish a theoretical framework for understanding spectral transitions in systems with imaginary Stark potentials, with potential realizations in photonic frequency synthetic dimensions.

Quantum communication provides us with a novel means of secure information transmission. Concurrently, there is a growing demand for multi-user quantum networks in tandem with the development of quantum communication devices. Given that most terrestrial quantum networks rely on optical fibers, the escalating user demand has rendered the cost and complexity of multi-fiber links critical issues that demand immediate attention. This article presents a duplex quantum communication link optimization scheme. This scheme significantly reduces the consumption of fiber link resources in duplex quantum communication systems, simplifies the deployment process, and cuts down costs. Based on this scheme, a corresponding experimental system was constructed and tested. The test results demonstrate that the scheme effectively simplifies the link without significantly compromising the performance of the original system.

In quantum information processing, the development of fast and robust control schemes remains a central challenge. Although quantum adiabatic evolution is inherently robust against control errors, it typically demands long evolution times. In this work, we propose to achieve rapid adiabatic evolution, in which nonadiabatic transitions induced by fast changes in the system Hamiltonian are mitigated by flipping the nonadiabatic transition matrix using π pulses. This enables a faster realization of adiabatic evolution while preserving its robustness. We demonstrate the effectiveness of our scheme in both two-level and three-level systems. Numerical simulations show that, for the same evolution duration, our scheme achieves higher fidelity and significantly suppresses nonadiabatic transitions compared to the traditional STIRAP protocol.

Quantum networks play a pivotal role in the advancement of quantum technologies, expanding the scope of applications and communication distances. However, the absence of practical quantum repeaters poses a significant obstacle to large-scale network construction. Trusted repeater networks, on the other hand, utilize classical trusted repeaters to connect users, thereby sacrificing the information-theoretic security advantage inherent in quantum communication. In this study, we propose a scheme for constructing a fully quantum network in which any two users are directly connected via a switchable optical router, ensuring information-theoretic security across the entire network with existing technologies. Considering that the practical point-to-point quantum communication distance in optical fibers has reached 100 km, our scheme effectively addresses the challenge of building a fully quantum network within an urban area. A 40-km-long functional quantum network has been established using commercial optical links, enabling full operations of tasks such as quantum secure direct communication and quantum key distribution.

The Riemann Hypothesis (RH), one of the most profound unsolved problems in mathematics, concerns the nontrivial zeros of the Riemann zeta function. Linking these zeros to physical phenomena offers new perspectives on their origin and verification. Here we establish a direct correspondence between these zeros and dynamical quantum phase transitions in two complementary engineered quantum many-body systems, characterized by the average accumulated phase factor and the Loschmidt amplitude, respectively. This precise correspondence recasts the RH as the occurrence of phase transitions at a unique temperature and identifies it as a previously unknown transition mechanism. We demonstrate this correspondence in a proof-of-principle experiment on a quantum processor. Moreover, we propose a quantum computational framework that implements both systems with polynomial resources, suggesting quantum advantage in probing the hypothesis. Our work bridges nonequilibrium quantum dynamics and number theory, positioning quantum computing as a powerful platform for exploring mathematical conjectures, phase transitions and beyond.

Real-time decoding is a critical bottleneck for large-scale fault-tolerant quantum computing. AI-based neural pre-decoders locally correct most physical errors before passing residual syndromes to a global decoder, enabling sub-microsecond latencies. However, existing architectures carry significant overhead from dense 3D convolutions. We present QuantiSpect, a lightweight 3D convolutional neural network (CNN) pre-decoder for the rotated surface code, built on the decoding pipeline of Chamberland et al. The key idea is to replace the dense 3D convolutions with three parallel branches in each residual block: a depthwise spatial branch, a depthwise temporal branch, and a grouped spatio-temporal branch, followed by a squeeze-and-excitation channel gate. This reflects the structure of surface code errors, where spatial and temporal syndrome correlations are partially separable. On a unified 4xA100 GPU benchmark, QuantiSpect matches the receptive field of the Accurate baseline at R=13 while using 2.71x fewer parameters (0.663M vs 1.80M) and 2.84x fewer per-voxel convolutional MACs. It matches Accurate's circuit-level threshold and accuracy at moderate and large code distances, reduces the logical error rate by up to 1.85x relative to uncorrelated PyMatching at d=13, p=0.5

Variational quantum learning is traditionally constrained to unitary dynamics, often treating quantum channels as detrimental noise. In this work, we reformulate the quantum channels as trainable computational primitives and establish a non-unitary quantum machine learning framework grounded in open-system dynamics. We demonstrate that the outputs of channel-enhanced quantum models form a structured superposition of multiple functional components. Each component is governed by an effective observable whose spectrum can be adaptively modulated during training, a significant departure from the spectral invariance in unitary transformations. Moreover, the proposed framework generalizes conventional unitary quantum models by retaining them as a special case while introducing additional non-unitary degrees of freedom. Furthermore, we reveal that trainable quantum channels enrich the optimization geometry through ensemble-averaged gradient and additional optimization directions induced by the Kraus operators. Extensive experiments on classification tasks using trainable amplitude-damping and phase-damping channels confirm enhanced optimization dynamics and predictive performance. In addition, we experimentally validate the proposed framework through hardware inference using ten-qubit quantum models implemented on the superconducting quantum processor, confirming its practical feasibility and hardware compatibility. Our work provides a principled approach for leveraging quantum channels as trainable resources and advances the design of high-performance quantum learning architectures.

Variational quantum algorithms (VQAs) have emerged as a promising approach to quantum cryptanalysis on noisy intermediate-scale quantum (NISQ) devices. Although numerous variational attack schemes have been proposed for symmetric cryptosystems, a systematic and modular benchmarking framework to evaluate their performance is still lacking. In this work, we present a comprehensive benchmark study of variational quantum attacks on the Simplified Data Encryption Standard (S-DES), focusing on the modular design choices that determine attack efficiency. We formulate variational quantum attacks within a unified framework consisting of four components: initial state preparation, parameterized circuit (Ansatz) design, cost function construction, and classical optimization. Through numerical simulations, we systematically compare representative design alternatives and evaluate their combinations in terms of convergence behavior, success probability, and effective time complexity. We further introduce standardized metrics for assessing variational quantum attack performance. Our results reveal clear performance hierarchies among different modular configurations and show that carefully optimized designs can significantly outperform naive quantum search. This work establishes a principled benchmark methodology for variational quantum cryptanalysis and positions S-DES as a practical testbed for evaluating quantum attacks on symmetric ciphers in the NISQ era.

We study a continuum Hatano–Nelson model with a saturating nonlinear nonreciprocity and analyze its stationary states via the associated phase-space flow. We uncover a global scenario controlled by a subcritical Hopf bifurcation and a saddle-node of limit cycles, which together generate a finite coexistence window. In this window, skin modes and extended states are both stable at a fixed energy E, separated by a nonlinear basin separatrix in phase space rather than a spectral (mobility-edge) mechanism in a linear system. An averaged amplitude equation yields closed-form predictions for the limit-cycle branches and the SNLC threshold. Building on the basin geometry, we introduce a basin-fraction order parameter that exhibits a first-order-like jump at SNLC. Intriguing physical phenomena in the coexistence window are also revealed, such as separatrix-induced long-lived spatial transients and hysteresis. Overall, our findings highlight that, beyond linear spectral concepts, global attractor-basin geometry provides a powerful and complementary lens for understanding stationary states in nonlinear non-Hermitian systems.

Achieving quantum advantage remains a milestone in the noisy intermediate-scale quantum era. Without complexity proofs, scaling advantage-where quantum resource requirements grow more slowly than their classical counterparts-is the primary indicator. However, direct applications of quantum optimization algorithms to classically intractable problems have yet to demonstrate this advantage. Here we develop enhanced quantum solvers for the NP-complete one-in-three Boolean satisfiability problem. We propose a restricting space reduction algorithm that achieves optimal search-space dimensionality under mod-2 arithmetic, thereby reducing qubit requirements and time complexity. Numerical studies on instances with up to 70 variables demonstrate that our enhanced quantum approximate optimization algorithm- and quantum adiabatic algorithm-based solvers outperform state-of-the-art classical solvers; the quantum adiabatic algorithm-based solver serves as a lower-bound reference while retaining scaling advantage. Furthermore, experiments on a 13-qubit superconducting processor confirm the predicted improvements. Collectively, our results provide empirical evidence of quantum speedup for an NP-complete problem.

We propose a disorder-free one-dimensional single-particle Hamiltonian hosting an exact mobility edge (ME), placing the system outside the assumptions of no-go theorems regarding unbounded potentials. By applying a linear Stark potential selectively to one sublattice of a dimerized chain, we generate an effective Hamiltonian with unbounded, staggered hopping amplitudes. The unbounded nature of the hopping places the model outside the scope of the Simon-Spencer theorem, while the staggered scaling allows it to evade broader constraints on Jacobi matrices. We analytically derive the bulk spectrum in reciprocal space, identifying a sharp ME where the energy magnitude equals the intercell hopping strength. This edge separates a continuum of extended states from two distinct localized branches: a standard unbounded Wannier-Stark ladder and an anomalous bounded branch accumulating at the ME. The existence of extended states is supported by finite-size scaling of the inverse participation ratio up to system sizes L similar to 109. Furthermore, we propose an experimental realization using photonic frequency synthetic dimensions. Our numerical results indicate that the ME is robust against potential experimental imperfections, including frequency detuning errors and photon loss, establishing a practical path for observing MEs in disorder-free systems.