AAPPS Bulletin最新文献

The XY spin chain is a paradigmatic example of a model solved by free fermions, in which the energy eigenspectrum is built from combinations of quasi-energies. In this article, we show that by extending the XY model’s anisotropy parameter (lambda) to complex values, it is possible for two of the quasi-energies to become degenerate. In the non-Hermitian XY model, these quasi-energy degeneracies give rise to exceptional points (EPs) where eigenvalues and their corresponding eigenvectors coalesce. The distinct (lambda) values at which EPs appear form concentric rings in the complex plane which are shown in the infinite system size limit to converge to the unit circle coinciding with the boundary between distinct topological phases. The non-Hermitian model is also seen to possess a line of broken (mathcal{P}mathcal{T}) symmetry along the pure imaginary (lambda)-axis. For finite systems, there are four EP values on this broken (mathcal{P}mathcal{T})-symmetric line if the system size is a multiple of 4.

Over the past four decades, quantum communication has evolved as a dynamic interdisciplinary field, advancing theoretical concepts and practical implementations. This article provides a concise overview focusing on recent progress in different aspects of secure quantum communication and quantum computation protocols, which can be applied to several real-world applications in quantum networks. These protocols guarantee unconditional security while enhancing communication rates and computation capabilities by harnessing quantum advantages. We also explore the role of non-terrestrial networks in quantum applications, with a focus on quantum technologies such as quantum key distribution and beyond, suitable for satellite-based applications. These technologies can contribute to future extensions of the quantum internet across intercontinental territories, connecting complex quantum network applications. Further, we delve into discussing the integration of quantum communication into 6G technology. The key innovation of this article lies in integrating quantum communication into 6G networks through a novel system-level simulation framework. 6G-enabled quantum networks are expected to meet the high demands on ubiquitous coverage, data rate, latency, and energy consumption. To address these issues, we design and evaluate four traffic demand scenarios using numerical simulation, illustrating how superdense coding doubles the data transmission rate and fulfills the high traffic demands on data rate, while under low traffic demand, entanglement resources can be reserved for future applications. Specifically, our investigation demonstrates how resource utilization adapts to different traffic demands, with adjustments based on available resources and practical constraints, evaluated over an ideal noise-free communication channel. The proof-of-work simulation is implemented using Python and is based on the system model we designed for varying traffic demands to pave the way for efficient quantum networks and gain deeper insights into their feasibility with available resources.

Near-term quantum devices offer promising avenues for addressing the electronic structure problem in quantum chemistry, yet their limited qubits and susceptibility to noise constrain algorithmic scalability. Although the variational quantum eigensolver (VQE) has shown potential for small-scale systems, further improvements are necessary to handle large basis sets and large many-electron molecules efficiently. In this work, we introduce RO-VQE, an improved approach derived from the earlier optimized orbital algorithm that employs a randomized procedure for selecting and optimizing orbitals. We evaluate RO-VQE on hydrogen chains systems (H₂ and H₄)—a well-established benchmark for quantum chemistry methods—using minimal, split-valence, and correlation-consistent basis sets. For these systems, RO-VQE improves ground-state energy estimations compared to conventional VQE methods, matching the accuracy of systematic strategies in these test cases. These proof-of-concept results suggest that randomized active-space selection may offer a practical compromise in NISQ-era quantum computations, offering a flexible alternative to more deterministic methods, particularly for systems constrained by limited quantum resources.

In this work, we introduce an explicit P-wave to construct the diquarks ([qc]_{widehat{V}}), then construct the local four-quark currents to explore the hidden-charm tetraquark states with the (J^{PC}=0^{++}), (1^{+-}), and (2^{++}) in the framework of the QCD sum rules at length. Our calculations indicate that the light-flavor SU(3) breaking effects on the tetraquark masses are tiny. The predictions support assigning the X(4475) and X(4500) as the ([uc]_{widehat{V}}[overline{uc}]_{widehat{V}}-[dc]_{widehat{V}}[overline{dc}]_{widehat{V}}) and ([sc]_{widehat{V}}[overline{sc}]_{widehat{V}}) tetraquark states with the (J^{PC}=0^{++}) respectively, and assigning the (Z_{c}(4600)) and (Z_{bar{c}bar{s}}(4600)) as the ([uc]_{widehat{V}}[overline{dc}]_{widehat{V}}) and ([qc]_{widehat{V}}[overline{sc}]_{widehat{V}}) tetraquark states with the (J^{PC}=1^{+-}) respectively. On the other hand, there is no room for the X(4710) and X(4700). Combined with previous works, the X(4475), X(4500), (Z_{c}(4600)), and (Z_{bar{c}bar{s}}(4600)) might have other important Fock components besides the (widehat{V}widehat{V}) type components.

The variation of edge confinement modes such as L-mode, H-mode, QH-mode, and I-mode and transitions between these modes in toroidal devices is attributed to interplay between turbulent inflow plasmas from divertor and outflow plasmas from the edge in magnetic configuration with x-point. A concept of flow impedance is introduced to model edge confinement of plasmas in tokamak and stellarator. The core confinement improvement is largely due to effective core heating profile, and direct ion heating with PNB system is favorable compared to electron heating in generation of sufficient α-power essential for sustaining the ignition state. Validation of transition physics of sustained ignition state from external to internal α-heating is critical for design of the next step magnetic fusion device. The most probable path for a compact ignition test device in magnetic fusion is suggested. The device size and expected performance of a tokamak plasma are projected based on critical review of experimental data of magnetic fusion research accumulated for half a century such as τ_E scaling laws and n_iτ_ET_i data. A tokamak plasma, V_p ~ 240 m³, equipped with direct ion heating system that can yield fusion power of ~ 220 MW (i.e., α-power up to ~ 45 MW) may be sufficient to test ignition state and transition physics. Practical actuators for control of the core and edge confinement which can be developed based on effective core heating and control of inflow plasmas from divertor are suggested.

The Electron-Ion Collider (EIC) is the world’s first electron + heavy-ion collider, and also performs polarized electron + polarized proton and light ion collisions, that will be constructed at Brookhaven National Laboratory in the USA. It will explore new areas of quantum chromodynamics (QCD) and foster the richness of nuclear and hadron physics. The EIC program will produce many new and very extensive results in nuclear and hadron physics over the next few decades. As an international cooperation project, it is essential for the future development of this field in Asia to focus on taking the lead in this EIC project.

Magnetic resonance wireless power transfer (WPT) has emerged as a pivotal technology for near-field electromagnetic manipulation, enabling wire-free energy delivery across diverse applications ranging from consumer electronics and implantable medical devices to electric vehicles. While near-field coupling facilitates this paradigm shift, it imposes inherent constraints: the exponential decay of coupling strength fundamentally limits transfer distance to short-to-mid ranges, and complex power delivery pathways—exemplified by robotic arms—necessitate relay coils configured in domino-like arrays. Conventional domino architectures, however, suffer from significant drawbacks including detrimental frequency splitting due to multi-coil near-field coupling, exacerbated system losses under load, and an inherent lack of precise spatial control over energy delivery. To overcome these limitations, we introduce a customized WPT paradigm based on a one-dimensional non-Hermitian chain with engineered iso-spectral modulation. Through precise control of inter-resonator coupling strengths following a parabolic profile, we achieve an equally spaced eigenvalue spectrum. Crucially, frequency-selective excitation enables deterministic and customized energy localization at predetermined sites within the chain. This approach not only provides a novel platform for developing advanced WPT systems, particularly for simultaneous multi-target energy delivery, but also deepens the fundamental understanding of complex energy transfer dynamics governed by tailored coupling and non-Hermitian physics.

By using both diagrammatic theory and Chevy ansatz approach, we derive an exact set of equations, which determines the spectral function of Fermi polarons with multiple particle-hole excitations at nonzero temperature. In the diagrammatic theory, we find out the complete series of Feynman diagrams for the multi-particle vertex functions, when the unregularized contact interaction strength becomes infinitesimal, a typical situation occurring in two- or three-dimensional free space. The latter Chevy ansatz approach is more widely applicable, allowing a nonzero interaction strength. We clarify the equivalence of the two approaches for an infinitesimal interaction strength and show that the variational coefficients in the Chevy ansatz are precisely the on-shell multi-particle vertex functions divided by an excitation energy. Truncated to a particular order of particle-hole excitations, the set of equations can be used to approximately calculate the finite-temperature polaron spectral function, once the numerical singularities in the equations are appropriately treated. As a concrete example, we calculate the finite-temperature spectral function of Fermi polarons in one-dimensional lattices, taking into account all the two-particle-hole excitations. We show that the inclusion of two-particle-hole excitations quantitatively improve the predictions on the polaron spectral function. Our results provide a useful way to solve the challenge problem of accurately predicting the finite-temperature spectral function of Fermi polarons in three-dimensional free space. In addition, our clarification of the complete set of Feynman diagrams for the multi-particle polaron vertex functions may inspire the development of more accurate diagrammatic theories of population-imbalanced strongly interacting Fermi gases, beyond the conventional many-body T-matrix approximation.

We attempt to propose the first orthogonal-state-based protocols of measurement-device-independent quantum secure direct communication and quantum dialogue employing single basis, i.e., Bell basis as decoy qubits for eavesdropping detection. Orthogonal-state-based protocols are inherently distinct from conventional conjugate-coding protocols, offering unconditional security derived from the duality and monogamy of entanglement. Noise imposes a major challenge to the efficient implementation of these measurement-device-independent based secure direct quantum communication protocols. Notably, these orthogonal-state-based protocols demonstrate improved performance over conjugate-coding-based protocols under certain noisy environments, highlighting the significance of selecting the best basis choice of decoy qubits for secure quantum communication under collective noise. Further, we rigorously analyze the security of the proposed protocols against various eavesdropping strategies, including intercept-and-resend attack, entangle-and-measure attack, information leakage attack, flip attack, and disturbance or modification attack. Our findings also show that, with appropriate modifications, the proposed orthogonal-state-based measurement-device-independent quantum secure direct communication protocol can be transformed into orthogonal-state-based measurement-device-independent versions of quantum key distribution and quantum key negotiation protocols, expanding their applicability. Our protocols leverage fundamentally distinct resources to close the security loopholes linked to measurement devices, while also effectively doubling the distance for secure direct message transmission compared to traditional quantum secure direct communication protocols. Additionally, we calculate the efficiency of our proposed protocols and compare them with standard versions of measurement-device-independent quantum secure direct communication protocols. Ultimately, we discuss system and operational complexity of our proposed protocols in light of experimental elements and the processes.