Advanced quantum technologies最新文献

Non-Hermitian systems have attracted increasing attention in recent years, particularly those exhibiting Parity-Time (PT) symmetry. Quantum metrology establishes the ultimate attainable bounds for parameter estimation in both Hermitian and non-Hermitian systems. However, comparatively little is known about non-Hermitian systems with anti-Parity-Time (APT) symmetry. In this work, we investigate the theoretical bounds on quantum parameter estimation precision for an APT-symmetric system governed by the Bogoliubov–de Gennes (BdG) Hamiltonian. We explicitly derive the expression for the quantum Fisher information (QFI) and compare the attainable precision limits for both multiplicative and non-multiplicative parameters in the BdG Hamiltonian. Our analysis of the effective QFI reveals that quantum parameter estimation precision can be significantly enhanced as the system approaches the exceptional point with unbroken APT symmetry, where Heisenberg scaling becomes achievable. We also examine how the effective QFI depends on the choice of initial states. Furthermore, we demonstrate that entanglement in multi-particle initial state can provide an additional enhancement to the QFI. The ratio of limit of parameter estimation precision of the entangled state to the greatest one we have found over all the tensor product states is 1.22, which is greater than 1. Our analysis of two-particle states confirms that entanglement in the initial state can further increase the QFI, highlighting it as a valuable quantum resource. These findings lay a theoretical foundation for future experimental explorations of parameter estimation in APT-symmetric non-Hermitian systems.

Based on the Sagnac effect, we propose how to achieve nonreciprocal strong mechanical squeezing via periodic driving in a spinning microdisk optomechanical system. We find that the strong nonreciprocal squeezing effect happens when the system is driven by a periodically modulated pump in a chosen port but not in the other. By appropriately choosing the ratio of the optomechanical coupling sidebands, the squeezing degree in the steady state can far surpass the 3-dB limit. We provide a detailed analysis of the underlying nonreciprocal squeezing mechanism by introducing the Bogoliubov mode and demonstrate that cooling it into ground state is the decisive factor to generate the nonreciprocal squeezing effect. We show that the proposed scheme has strong robustness against thermal noise and even for high thermal phonon occupation number $��2�\times �{10}^3�$, the 3-dB squeezing limit still can be broken. Specifically, by utilizing the technique of adiabatic elimination of cavity mode, we obtain the analytical result of nonreciprocal squeezing, which matches very well with the numerical simulation. We also demonstrate that the generated nonreciprocal squeezing can be effectively measured by the output field in the experiment. Our scheme provides a potential path to manipulate nonreciprocal mechanical squeezing and also has significant applications ranging from nonreciprocal quantum metrology to directional quantum communication.

Quantum secret sharing (QSS) holds a significant place in quantum cryptography. Unlike traditional QSS schemes, which often simplistically model participants as either completely honest or fully malicious, rational QSS introduces a more realistic framework by modeling participants as rational entities who strategically act to maximize their own utility. In this paper, for the first time, a rational quantum multi-secret sharing scheme designed to share a classical bit string by configuring multiple effective reconstruction rounds is proposed. Further, a novel method is proposed to facilitate equilibrium achievement—deception deterrence. In terms of efficiency, the scheme achieves, for the first time, an effective reconstruction round ratio $��{\eta }_0�=�\frac{1}{4}�$ and a communication efficiency $��\eta �=�\frac{1}{�8�(�2�t�-�1�)�}�$ are independent of the total number of reconstruction rounds $��r�+�w�$ configured in the scheme, overcoming the communication efficiency limitation inherent in existing schemes. In terms of equilibrium achievement, the proposed new method not only returns to the essence of strategic interaction among rational participants themselves but also avoids the substantial verification cost.

A second-order topological photonic crystal design based on an all-dielectric silicon platform is proposed, featuring truncated rectangular air holes to realize a wide common photonic bandgap. A polarization-independent topological corner state (TCS) cavity is constructed, realizing degenerate resonant frequencies for both transverse electric and transverse magnetic polarizations via geometric optimization. By integrating this TCS cavity with a dual-polarization topological edge state waveguide, a compact topological cavity-waveguide coupled system is formed, demonstrating asymmetric Fano resonances for both polarizations, which arise from the interference between localized corner states and propagating edge states. This system achieves ultrahigh quality factors, high refractive index sensing sensitivities along with exceptional figures of merit, and excellent robustness against structural imperfections. It offers promising prospects for practical applications in polarization-division multiplexing, integrated photonic circuits, refractive index sensors, and quantum information technologies.

A quantum-enhanced scheme for microwave (MW) electric (E) field detection is theoretically proposed, utilizing transient amplification without inversion (AWI) in cold ⁸⁷Rb atoms. It is achieved by modulating a continuous-wave coupling laser into a periodic near-square-wave pulse, which enables precise control over quantum coherence and induces transient gain. Simulation results demonstrate significant performance enhancements of the AWI scheme compared to conventional electromagnetically induced transparency (EIT) approaches. In comparison, the AWI scheme shows 7.3 times enhanced transient transmission intensity. The reduction of the full width at half maximum from 0.54 × 2π to 0.15 × 2π MHz represents a 72% narrowing of the spectral linewidth, which enables superior spectral resolution and extends the range of measurable Autler-Townes splitting. Furthermore, the minimum detectable MW E-field strength of 172.8 nV cm⁻¹ represents an order of magnitude improvement. The robustness of the AWI signal against simulated technical noise is also confirmed. The demonstrated capabilities establish AWI as a promising technique for high-sensitivity quantum MW electrometry.

We propose a novel quantum digital signature protocol that eliminates the need for a trusted third-party, a common limitation in existing quantum signature schemes. While the concept of third-party-free quantum signatures has been discussed in earlier works, such as Gottesman and Chuang (2001), no concrete protocol with provable information-theoretic security has been presented to date. Recent studies have explored computationally secure quantum signature schemes without trusted parties, but their security relies on assumptions about quantum computational hardness. In contrast, our protocol achieves information-theoretic unforgeability based solely on the non-cloning property of quantum states. It uses classical private keys and quantum public keys, and requires only single-qubit operations. The scheme also satisfies key security properties, including asymmetry, undeniability, and expandability, making it suitable for implementation in near-term quantum technologies.

In the node classification task on graphs, mainstream graph neural networks often adopt the same neighborhood aggregation strategy for all nodes. This approach results in biased learning toward features from the majority nodes while devaluing those from the minority nodes under class imbalance. In particular, for marginal nodes, limited neighboring information can severely impact classification performance. To address this challenge, this paper proposes a feature fusion-based hybrid quantum-classical graph residual neural network (QGRNN). Leveraging the nonlinear expressive capacity of qubits in modeling complex feature interactions, the model innovatively integrates a structure-driven node selection mechanism with a quantum feature enhancement module, while also dynamically fusing classical features and Hamiltonian expectation values through a gated residual fusion mechanism to compensate for representational deficiencies of marginal nodes overlooked by classical methods. Experimental results show that QGRNN consistently outperforms baselines across a range of node classification tasks. In binary and ternary classification settings, it exhibits strong discriminative capability and robustness, especially maintaining high accuracy under severe class imbalance. In addition, QGRNN also demonstrates strong generality in other tasks, in recommendation scenarios, achieving an average improvement of 36.3% on NDCG@5, 44.3% on Recall@5, and 21.9% on Recall@10 compared to the baseline.

State-of-the-art free-space continuous-variable quantum key distribution (CV-QKD) protocols use phase reference pulses to modulate the wavefront of a real local oscillator at the receiver, thereby compensating for wavefront distortions caused by atmospheric turbulence. It is normally assumed that the wavefront distortion in the phase reference pulses is identical to the wavefront distortion in the quantum signals, which are multiplexed during transmission. However, in real-world deployments, there can exist a relative wavefront error (WFE) between the reference pulses and quantum signals, which, among other deleterious effects, can severely limit secure key transfer in satellite-to-Earth CV-QKD. In this work, we introduce machine learning-based wavefront correction algorithms, which utilize multi-plane light conversion for decomposition of the reference pulses and quantum signals into the Hermite-Gaussian (HG) basis, then estimate the difference in HG mode phase measurements. Through detailed simulations of the Earth-satellite channel, we demonstrate that our algorithm can identify and compensate for any relative WFEs that may exist. We quantify the gains available in our algorithm in terms of the CV-QKD secure key rate. We show channels where positive secure key rates are obtained using our algorithms, while information loss without wavefront correction would result in null key rates.