1,217 research outputs found
Simulating periodic systems on quantum computer
The variational quantum eigensolver (VQE) is one of the most appealing
quantum algorithms to simulate electronic structure properties of molecules on
near-term noisy intermediate-scale quantum devices. In this work, we generalize
the VQE algorithm for simulating extended systems. However, the numerical study
of an one-dimensional (1D) infinite hydrogen chain using existing VQE
algorithms shows a remarkable deviation of the ground state energy with respect
to the exact full configuration interaction (FCI) result. Here, we present two
schemes to improve the accuracy of quantum simulations for extended systems.
The first one is a modified VQE algorithm, which introduces an unitary
transformation of Hartree-Fock orbitals to avoid the complex Hamiltonian. The
second one is a Post-VQE approach combining VQE with the quantum subspace
expansion approach (VQE/QSE). Numerical benchmark calculations demonstrate that
both of two schemes provide an accurate enough description of the potential
energy curve of the 1D hydrogen chain. In addition, excited states computed
with the VQE/QSE approach also agree very well with FCI results
Rapid thermal annealing and crystallization mechanisms study of silicon nanocrystal in silicon carbide matrix
In this paper, a positive effect of rapid thermal annealing (RTA) technique has been researched and compared with conventional furnace annealing for Si nanocrystalline in silicon carbide (SiC) matrix system. Amorphous Si-rich SiC layer has been deposited by co-sputtering in different Si concentrations (50 to approximately 80 v%). Si nanocrystals (Si-NC) containing different grain sizes have been fabricated within the SiC matrix under two different annealing conditions: furnace annealing and RTA both at 1,100°C. HRTEM image clearly reveals both Si and SiC-NC formed in the films. Much better "degree of crystallization" of Si-NC can be achieved in RTA than furnace annealing from the research of GIXRD and Raman analysis, especially in high-Si-concentration situation. Differences from the two annealing procedures and the crystallization mechanism have been discussed based on the experimental results
Lagging propagation phase of spatially structured beams
The structured beams especially with spatially varying phase distribution have attracted tremendous attention in both physics and engineering. Recently, studies have shown that the transverse spatial confinement of optical fields or photons leads to a modification of the group velocity but the phase velocity of propagating structured beams is revealed insufficiently in the experiments. In this work, we provide the theoretical model and experimental observation of propagation phase of structured beams. The analysis suggests that the spatially structured beams with a definite axial component of wavevector kr carry a so called “lagging propagation phase”, which can be considered as a generalized Gouy phase that originally appears within a focal region. Taking the higher-order Bessel beam as an example, the propagation phase difference is demonstrated by mapping to the rotating angle of intensity patterns superposed with different radial and angular phase gradients. Physically, the lagging propagation phase may provide an interpretation for the dynamic evolution of complex structured beams or interfering fringes upon propagation such as the vortex knots or braids. From the application aspect, the lagging propagation phase would facilitate a promising way for structured beams in optical sensing and metrology
Controlled generation of Poincar\'e sphere beams with inverse-designed multimode meta-waveguides
The angular momentum of light can be described by positions on various
Poincar\'e spheres, where different structured light beams have proven useful
for numerous optical applications. However, the dynamic generation and control
of arbitrary structured light on different Poincar\'e spheres is still handled
via bulky optics in free space. Here we propose and demonstrate multimode
silicon photonic integrated meta-waveguides to generate arbitrary structured
light beams on polarization/orbit/higher-order/hybrid Poincar\'e spheres. The
multimode meta-waveguides are inversely designed to map polarization
states/higher-order spatial modes to orbit angular momentum, generating
polarization-/charge-diverse orbit angular momentum modes. Based on the
fundamental orbit angular momentum mode basis enabled by the meta-waveguides,
different structured-light fields on polarization/orbit/higher-order/hybrid
Poincar\'e spheres could be flexibly generated by controlling the relative
amplitude and phase profiles of on-chip guided modes. The demonstrated photonic
integrated devices hold great potential for the flexible manipulation of
structure light beams in many applications
Let's Chat to Find the APIs: Connecting Human, LLM and Knowledge Graph through AI Chain
API recommendation methods have evolved from literal and semantic keyword
matching to query expansion and query clarification. The latest query
clarification method is knowledge graph (KG)-based, but limitations include
out-of-vocabulary (OOV) failures and rigid question templates. To address these
limitations, we propose a novel knowledge-guided query clarification approach
for API recommendation that leverages a large language model (LLM) guided by
KG. We utilize the LLM as a neural knowledge base to overcome OOV failures,
generating fluent and appropriate clarification questions and options. We also
leverage the structured API knowledge and entity relationships stored in the KG
to filter out noise, and transfer the optimal clarification path from KG to the
LLM, increasing the efficiency of the clarification process. Our approach is
designed as an AI chain that consists of five steps, each handled by a separate
LLM call, to improve accuracy, efficiency, and fluency for query clarification
in API recommendation. We verify the usefulness of each unit in our AI chain,
which all received high scores close to a perfect 5. When compared to the
baselines, our approach shows a significant improvement in MRR, with a maximum
increase of 63.9% higher when the query statement is covered in KG and 37.2%
when it is not. Ablation experiments reveal that the guidance of knowledge in
the KG and the knowledge-guided pathfinding strategy are crucial for our
approach's performance, resulting in a 19.0% and 22.2% increase in MAP,
respectively. Our approach demonstrates a way to bridge the gap between KG and
LLM, effectively compensating for the strengths and weaknesses of both.Comment: Accepted on ASE'202
Parameter Uncertainty Effects of Stiffeners on the Vibration of Plates
The paper concerns parameter uncertainty effects of rib-stiffeners on the vibro-acoustics of thin plate structures. To gain a deep insight into the uncertainty propagation mechanism, a simple beam-stiffened plate model is built up in the first instance. By a simple mode-based hybrid technique, both the dynamic response of the beam and the statistical energy response of the plate can be approximated as functions of the beam natural frequency variations. It is found that if the amount of beam uncertainty is small enough (e.g., the generated set of natural frequency variations is narrower than the corresponding half-power bandwidth of the resonant modes), the real part of the beam mobility tends to be affected relatively little compared to the imaginary part. As a result, only the phase part of the dynamic response of the beam tends to be affected while the amplitude part can be affected relatively slightly. This is especially true when the beam and the plate have a large dynamic mismatch. One can thus deduce that, for stiffened-panel structures, the parameter uncertainties of stiffeners tend to affect little the structure-borne-sound transmission between ribs and the panel foundations. Numerical investigations of different rib-stiffened plates were conducted to validate the main conclusions
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