Quantum secure direct communication (QSDC), a vital branch of quantum communication, enables reliable, secure transmission under harsh conditions of high channel noise, large optical loss and stringent security constraints. Having undergone field trials and practical deployment, QSDC serves as a promising candidate for confidential transmission in ultra-high-security scenarios. Modern society relies heavily on ubiquitous communication, and 5G mobile networks have achieved rapid development and widespread commercialization in recent years, driving growing demands for robust 5G security. This paper proposes a QSDC-5G integrated secure transmission architecture to safeguard 5G data delivery. The solution maintains full compatibility with legacy classical networks while satisfying long-term security requirements for future communications. Laboratory simulation and stability tests were conducted on the proposed converged security network. Continuous 24-hour measurements demonstrate that the integrated network achieves an interface throughput of 12 kbps with a round-trip latency below 3500 ms. These key metrics satisfy the signaling transmission demands for single mobile terminal authentication when accessing private networks via base stations, laying a solid foundation for deep integration of QSDC into 5G systems.
The quantum internet is evolving from isolated point-to-point quantum key distribution links toward a globally interconnected, multi-layer protocol stack supporting entanglement distribution, quantum teleportation, and distributed quantum computing. As this architecture matures, each protocol layer-physical, link, network, transport, and application exposes negotiable security parameters: QKD protocol type, entanglement fidelity thresholds, purification rounds, error-correction schemes, and authentication methods. Yet no standardized mechanism exists to negotiate these parameters securely across layers or to prevent adversarial downgrade. The classical internet spent two decades rediscovering this lesson through attacks such as POODLE, FREAK, Logjam, KNOB, and Dragonblood; the quantum internet is now repeating the same architectural oversight. This study introduces QShield, a cross-layer security negotiation framework that binds every layer’s capability commitment into a unified transcript hash, ensuring that any single-layer downgrade invalidates the session-wide security context. We formalize a quantum security downgrade hierarchy spanning six levels from device-independent QKD to classical cryptography and identify twelve concrete downgrade attack vectors mapped from classical analogs. Evaluation across all twelve attack types shows that QShield with cross-layer transcript binding achieves 100
Quantum photonic simulators are pivotal for designing and analyzing quantum photonic circuits that utilize both continuous-variable (CV) and discrete-variable (DV) encodings. This review critically examines the transition from Gaussian to non-Gaussian photonic models and the computational overhead that emerges from simulating systems with more than 20 modes or photon numbers exceeding 10 per mode. Gaussian states; such as coherent and squeezed states, are modeled efficiently using first-moment vectors and covariance matrices of dimension 2n × 2n , where n is the number of modes. Non-Gaussian elements like the cubic phase gate U = exp (i γx̂^3) and photon-subtracted states demand full Fock space representations and scale exponentially with photon number d^2 , where d is the Hilbert space dimension. We analyze simulators including Strawberry Fields, Piquasso, and Perceval, benchmarking their support for tensor networks (bond dimension D >100), GPU acceleration, thus NVIDIA A100 with 1555 GB/s bandwidth, and SoC implementations such as Edge TPU with 8 TFLOPS. Special focus is given to noise models such as photon loss with transmissivity η, thermal noise modeled with n̅ = 1.5 , and dark count Poisson distributions ( λ = 0.1 ). The review underscores scalable techniques and hybrid quantum-classical workflows vital for near-term photonic quantum computing.
Scalable quantum networks require quantum interfaces that coherently connect stationary matter qubits with flying photonic qubits. In solid-state defect platforms, such interfaces require coordinated optical excitation, microwave spin control, photon detection, and feedback with nanosecond-level timing, while conventional instrument-based control systems become increasingly difficult to scale as experimental protocols grow in complexity. Here we present an open-source FPGA control architecture for solid-state spin–photon interface experiments. Built on the Quantum Instrumentation Control Kit (QICK), the platform extends the existing FPGA overlay by integrating a programmable multi-channel single-photon counter, enabling photon-count–centric experiment execution while preserving compatibility with the QICK software ecosystem. This architecture integrates time-gated single-photon detection with synchronized RF, microwave, and digital control within a unified hardware environment. Using single nitrogen-vacancy (NV) centers in diamond, we experimentally validate the platform through microwave spin manipulation, resonant optical control, automated measurement routines, and time-bin–encoded spin–photon correlation protocols relevant to quantum networking. These results establish an extensible and experimentally validated control framework for solid-state spin–photon interfaces, with clear potential to accelerate the development of scalable quantum-network nodes.
Rydberg atomic receivers (RARs) have emerged as a promising candidate for next-generation wireless communication systems due to their broadband tunability, SI traceability, compact configuration, and omnidirectional reception. Currently, the primary challenge hindering the further large-scale deployment of RARs lies in the low data transmission rates, which is attributed to the narrow instantaneous bandwidth. This work improves data transmission rates from a signal processing perspective, proposing a cost-effective and operationally efficient solution. The Rydberg-atom-based electro-optic conversion (RAEOC) system behaves as a linear system under strong local oscillator biasing and small-signal excitation. Specifically, we develop a dynamic response model for the RAEOC system and derive its frequency-response expression via time-dependent perturbation theory, Laplace transformation, and vectorization-based computation. Furthermore, we establish a comprehensive RAR communication simulation framework. Monte Carlo simulations demonstrate that the frequency-domain estimation and equalization algorithm can significantly improve the bit error rate performance of RARs in broadband signal reception. Our equalization method suppresses inherent passband distortion in RAR systems to enhance data throughput under finite bandwidth.
Quantum annealing promises advantages for combinatorial optimization, but current hardware remains limited by sparse qubit connectivity. Encoding constrained problems onto these devices typically requires auxiliary variables that introduce dense couplings, degrading performance. Here we present prefix-sum encoding, which transforms coverage constraints into sequential variable chains with only nearest-neighbor interactions. We prove that a relaxed enforcement scheme, tracking whether coverage occurred rather than where, is mathematically equivalent to standard coverage while creating beneficial degeneracy in the solution landscape. Applied to haplotype inference, a hard problem in computational genomics, our encoding reduces qubit requirements by 18
We present an empirical model describing the detection response of single-photon detectors under pulsed illumination from a single-photon source based on a quantum dot. The model does not rely on assumptions about the recovery dynamics, but incorporates measured recovery functions to predict the effective detection efficiency. This model was successfully validated through a calibration of a superconducting nanowire single-photon detector at photon fluxes of up to 19 million photons per second at a wavelength of 929 nm. Calibrations of three silicon single-photon avalanche detectors with different dead times revealed deviations from the model predictions, suggesting an unaccounted influence of the different electronic design on the detector performance. Owing to its flexibility, the proposed model enables accurate estimation of photon fluxes from single-photon emitters and provides a practical tool for evaluating loss budgets of each component and therefore of entire quantum optical systems, thereby improving the overall system performance.
I present a physical-layer monitoring framework for quantum key distribution (QKD) implementations based on Krylov/operator-growth diagnostics. Running alongside standard parameter estimation, privacy amplification, and composable security proofs, it addresses a focused question: whether the temporal correlation structure of an observed quantum bit error rate (QBER) stream carries additional information about physical channel perturbations. Within a specified local-Hamiltonian channel model, the Lanczos coefficients of the channel Liouvillian define an operator-growth autocorrelation template, and deviations from it serve as anomaly scores for implementation monitoring. For the model studied here, the QBER autocorrelation relates to the operator autocorrelation through a proportionality relation, C_QBER(τ )=α (N)C_op(τ ), with α (N) an explicitly specified calibration factor. Local Hamiltonian perturbations generically distort the associated Krylov fingerprint once the perturbation reaches the support of the monitored observable, consistent with the locality of the Lanczos recursion and with Lieb–Robinson bounds. The resulting three-layer pipeline combines adaptive frequency filtering, Krylov-template extraction, and calibrated slope detection. On simulated BB84-like QBER data with realistic hardware noise, the detector achieves high anomaly discrimination under the tested perturbation classes (AUC=0.9899). On 181,606 public QBER measurements from a deployed fiber-optic QKD system, it yields a 4.5
Quantum annealing is a promising heuristic for combinatorial optimization, but on current hardware its solution quality degrades for larger and more complex problems due to noise and small energy gaps. Reverse annealing has been established as a refinement strategy, yet it remains unclear how problem characteristics, particularly the implemented quadratic unconstrained binary optimization (QUBO) matrix structure, influence refinement success and the optimal parameter regime. We find that combining forward and reverse annealing improves solution quality, with the magnitude of the improvement depending strongly on the problem class and corresponding QUBO size, while efficiency gains are tied to both annealing and problem-instance parameters. The benefits of reverse annealing increase with problem complexity and are strongest in regimes where forward annealing is increasingly limited. In these settings, reverse annealing yields larger efficiency gains than simply extending forward annealing times. We establish these results through a systematic experimental study on a D-Wave Advantage system, benchmarking reverse annealing across Max-Cut, Number Partitioning, and sparse clustering problems while varying reverse distance, pause duration, and annealing time. We identify optimal reverse annealing parameter regimes that depend on QUBO characteristics and are consistent with expected freeze-out behavior and with the energy-level-crossing structure observed for small representative instances. These findings demonstrate that reverse annealing is most valuable for large, high-complexity optimization problems and is likely to gain importance as quantum annealing hardware scales toward more realistic applications.
Joint remote implementation of quantum operations (JRIO) is crucial for distributed quantum computation. We propose a probabilistic JRIO scheme using a three-photon nonmaximally hyperentangled Greenberger-Horne-Zeilinger (GHZ) state, which is simultaneously entangled in the polarization and spatial-mode degrees of freedom (DOFs), as the shared quantum resource. This JRIO protocol operates on two core principles: transferring the quantum-state information of the target qubit to the senders’ joint system via polarization-DOF entanglement and applying local operations, then executing quantum operations on the receiver’s system using entanglement in the spatial-mode DOF. The construction of the proposed scheme requires weak cross-Kerr nonlinearities, X homodyne measurements, simple linear optical elements, and common single-photon detectors. This work extends the framework of the previous JRIO protocol to the scenario of a nonmaximally hyperentangled quantum channel, enriching the theoretical family of distributed quantum operation schemes.
Quantum technologies are increasingly framed as dual-use, raising concerns about civilian benefits alongside potential military and security applications. This paper examines how dual-use quantum technologies are communicatively constructed across four functionally differentiated domains: science, politics, the military, and business. Rather than treating dual-use as an inherent property of technology, we conceptualize it as a communicative category through which uncertainty, responsibility, and future expectations are negotiated. Drawing on Niklas Luhmann’s systems theory, we analyze a qualitative corpus of scientific publications, policy documents, military strategy reports, and business communications. We show that shared terms such as dual-use, security, and quantum advantage circulate across domains but acquire distinct meanings as they are re-embedded within domain-specific communicative codes. These translations generate both resonance and dissonance, producing structured misalignment rather than convergence. The paper contributes to our understanding of dual-use quantum technologies by reconstructing domain-specific articulations of dual-use, explaining their divergence through functional differentiation, and highlighting implications for responsibility, authority, and governance.
In this paper, we construct entanglement-assisted quantum error-correcting codes (EAQEC codes) of physical qubits p^s over 𝔽_p^m. We compare our EAQEC codes with all known EAQEC codes to see that our EAQEC codes are new in the sense that their parameters are different from all the previous constructions. If we fix the physical qubits and the logical qubits of EAQEC codes, many of them have larger quantum distances than the well known EAQEC codes in the literature. Moreover, some of our EAQEC codes achieve larger quantum distances while requiring fewer or the same number of entangled bits compared with existing EAQEC codes when the numbers of physical qubits and logical qubits are fixed. We construct asymmetric entanglement-assisted quantum error-correcting (AEAQEC) MDS codes of physical qubits p^s over 𝔽_p^m. When the physical qubits of the AEAQEC codes is fixed, many of our AEAQEC codes have a significantly larger number of quantum distances compared to all previously constructed AEAQEC codes. We also provide a version of Singleton bound for all AEAQEC codes.
Continued advancements in quantum computing have stimulated growing interest in translating quantum technologies into real-world applications. Consequently, the investigation of practically motivated NP-hard problems is of significant value. This study investigates the performance of a variational quantum eigensolver (VQE) in addressing the traveling salesperson problem (TSP) through noiseless simulations representative of noisy intermediate-scale quantum (NISQ) devices using higher-order binary optimization (HOBO) encodings. We construct a HOBO Hamiltonian with an efficient binary representation and propose an all-valid-state HOBO (AVS-HOBO) scheme based on cyclic mapping that eliminates one penalty term and reuses states that would otherwise be invalid. Using TSP instances of up to 20 cities, we compare the original HOBO and AVS-HOBO encodings from multiple perspectives, including the energy convergence behavior and the approximation, tour-length, and feasibility ratios. In addition to simulations, we perform computations on real quantum hardware with different device architectures, where we not only compare the performances of different chips but also investigate the effects of different error-mitigation methods on actual quantum machines. The results indicate that AVS-HOBO encoding enhances the practical reliability of VQE on NISQ devices and improves scalability for larger TSP instances, with broader applicability to constrained quantum optimization problems.
This work assesses the literature on QKD-PQC Hybrid Authenticated Key Exchange (HAKE) and related schemes, based on security proofs (e.g. availability of such a proof and underlying model), performance, and near-term implementation. We evaluate these protocols across diverse dual-use environments, ranging from strategic military SATCOM to high-value civilian infrastructure, such as banking backbones. The trade-offs among various solutions are discussed based on their Technology Readiness Level (TRL) and performance. Moreover, we identify specific use cases such as untrusted satellite nodes or long-distance terrestrial links which might require alternative measures depending on the operational requirements.
The development of novel technologies does not take place in a moral, economic, or geopolitical vacuum. Therefore, questions of funding, use-cases, and contexts of use will directly influence both moral and practical judgements around the ways in which these technologies are, or should be, developed and deployed. This article examines the growth of Quantum Technologies (QTs) in light of these challenges, and the ways in which they are already raising concerns with respect to questions of ‘dual-use’. The article argues that ‘dual-use’ as a category is inadequate for normative judgement as it conflates moral evaluation with a descriptive classification, and therefore misses important contextual and procedural elements. The article proposes making Responsible Innovation (RI) frameworks integral to the development of QTs in order to enable context-sensitive ethical assessment and decision-making guidance. Finally, the article proposes a way forward that engages with the principle-based concerns of those critical of military uses of QTs, while respecting the challenges posed by current geopolitical realities.
Cold-atom systems have emerged as a highly promising avenue for quantum-enhanced position, navigation, and timing applications. However, their wider adoption is currently hampered in part by the large footprint of the systems. In leveraging the miniaturisation possible through photonic integrated circuits, cold-atom sensors would be able to reach much wider commercial adoption. In this paper, we a propose a system for evanescently trapping 87Rb BECs using strip silicon nitride waveguides buried in silica using red- and blue-detuned fundamental and higher-order modes, providing a three-dimensional adjustable trap for BEC-based, chip-scale work in quantum science and technologies. Requiring no external lasers for PIC loading and capable of trapping bulk atom clouds, our method – when combined with other existing miniaturising technologies – can potentially produce shoebox or smaller sized deployable ultracold atom systems.
The recent developments of quantum technologies (QTs) have spurred growing interest for advancing applications of these technologies in many sectors including the military. Organizational and technical perspectives have been explored to shed light on implications for armed forces, however, only limited academic attention has been directed towards the connection between applications and operational environments. Consequently, this paper investigates the unique context of applying QTs to accomplish military tasks. This is examined through the theoretical model Technology-to-Performance Chain (TPC) by Goodhue and Thompson concerning task-technology fit and utilization. Firstly, two Danish national strategies and a NATO Challenge Programme are analyzed to identify similarities and differences in technology and task characteristics leading to potential fits. Secondly, the utilization aspect of the TPC model is explored by introducing a new framework that simultaneously enables a categorization of QTs according to both operational environments and contributions to task solution. In conclusion, the paper identifies potential fits between QTs and military tasks and specifies expected operational environments and task solutions of QTs. This paper thus advances the current understanding of how QTs can be applied in a military context with insights for other emerging and disruptive technologies as well as the ecosystems responsible for developing these technologies.
A hybrid optical pumping method employing a broad linewidth laser is proposed to enhance spin coherence and suppress virtual magnetic field noise in atomic magnetometers. The central frequency of broad linewidth laser is tuned to the resonance peak of the alkali-metal atoms D1 line. Its multiple frequency components suppress AC-Stark shift fluctuations caused by pumping laser frequency variations, thereby reducing virtual magnetic field noise. In addition, these components decrease the average optical absorption cross-section, improving the uniformity of atomic spin polarization, further enhancing spin coherence and extending transverse relaxation time. Experimental results show that, compared with narrow linewidth pumping, the proposed method suppresses virtual magnetic field noise by 17.95
Entanglement in high-dimensional systems plays a vital role in quantum information processing (QIP), as it extends the available Hilbert space, supports the manipulation of more intricate information, and broadens the scope of implementable quantum operations. In the paper, we present a deterministic scheme for the four-dimensional two-qudit Bell entangled state analysis for the four-photon system in the polarization degree of freedom, resorting to the weak cross-Kerr nonlinearity and some linear optical components. In our scheme, the analysis of four-dimensional Bell entangled state is constructed by three-photon Toffoli gate and quantum nondemolition detectors (QND1 and QND2). By phase shifts of the coherent beams, the 16 orthogonal four-dimensional two-qudit Bell states can be completely distinguished from each other. The proposal can be extended to the four-dimensional three-qudit entangled state analysis and n-qudit entangled state analysis. In addition, our deterministic scheme for high-dimensional entangled state analysis can be applied to high-dimensional quantum teleportation, including both uncontrolled and controlled quantum teleportation protocols. Moreover, our scheme can achieve high fidelity and efficiency, further broadening its applicability in high-dimensional QIP.
