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Effects of interface steps on the valley-orbit coupling in a Si/SiGe quantum dot
摘要： Valley-orbit coupling is a key parameter for a silicon quantum dot in determining its suitability for applications in quantum information processing. In this paper we study the effect of interface steps on the magnitude and phase of valley-orbit coupling for an electron in a silicon quantum dot. Within the effective-mass approximation, we ?nd that the location of a step on the interface is important in determining both the magnitude and the phase of the valley-orbit coupling in a Si/SiGe quantum dot. Speci?cally, our numerical results show that the magnitude of valley-orbit coupling can be suppressed up to 75% by a step of one atomic monolayer, and its phase can change by almost π . When two steps are present, the minimum value of the valley-orbit coupling can even approach zero. Our calculation can in principle be generalized to multiple steps as well, as long as the width of the regions between steps is much larger than the atomistic length scale. We also clarify the effects of an applied external magnetic ?eld and the higher orbital states on the valley-orbit coupling. Overall, our results illustrate that interface roughness can strongly affect both the magnitude and the phase of the valley-orbit coupling, which are crucial parameters for both spin and charge qubits in silicon.
关键词： interface steps,silicon quantum dot,effective-mass approximation,quantum information processing,valley-orbit coupling
更新于2025-09-11 14:15:04
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Optimized free-form surface modeling of point clouds from laser-based measurement
摘要： Freeform parameterizations to reproduce structure deformation are increasingly important topics in laser-scanner-based deformation analyses. High-accuracy assurance of free-form surface approximation is extremely critical for reliable deformation analysis. One main challenge in this field is the model selection. Improper model complexity could result in under-fitting the real object shape or overfitting data noises, and thus a failure of deformation analysis. A multi-sensor system could integrate advantages of different sensors and improve the quality of mission completed. This paper combines terrestrial laser scanning (TLS) and laser tracker (LT) technologies, to enhance high-accuracy surface modeling in deformation analysis. A surface-based B-spline approximation and a multi-sensor system are investigated, the latter of which focuses mainly on the combination of TLS and LT technologies. The innovation of this paper is that the surface-based B-spline approximation is validated and optimized with LT corner cube reflectors. Hypothesis testing is adopted to select the best parameter setting by judging most consistency of TLS and LT in various epochs. In the B-spline surface modeling, both instrumental and numerical uncertainties are considered. We use the instrumental uncertainty model based on intensity value, as well as numerical uncertainty based on adjustment theories. A sampling strategy is proposed to avoid data gaps and obtain even distributed data points.
关键词： multi-sensor,laser tracker,Surface modeling,B-spline approximation,terrestrial laser scanning
更新于2025-09-11 14:15:04
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Polarized Positron Beams via Intense Two-Color Laser Pulses
摘要： The generation of ultrarelativistic polarized positrons during the interaction of an ultrarelativistic electron beam with a counterpropagating two-color petawatt laser pulse is investigated theoretically. Our Monte Carlo simulation, based on a semiclassical model, incorporates photon emissions and pair productions, using spin-resolved quantum probabilities in the local constant field approximation, and describes the polarization of electrons and positrons for the pair production and photon emission processes, as well as the classical spin precession in between. The main reason for the polarization is shown to be the spin asymmetry of the pair production process in strong external fields, combined with the asymmetry of the two-color laser field. Employing a feasible scenario, we show that highly polarized positron beams, with a polarization degree of ζ ≈ 60%, can be produced in a femtosecond timescale, with a small angular divergence, ～74 mrad, and high density, ～1014 cm?3. The laser-driven polarized positron source raises hope for providing an alternative for high-energy physics studies.
关键词： polarized positron beams,ultrarelativistic electron beam,local constant field approximation,spin-resolved quantum probabilities,high-energy physics,Monte Carlo simulation,two-color laser pulses
更新于2025-09-11 14:15:04
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Driven quantum dot coupled to a fractional quantum Hall edge
摘要： We study a model of a quantum dot coupled to a quantum Hall edge of the Laughlin state, taking into account short-range interactions between the dot and the edge. This system has been studied experimentally in electron quantum optics in the context of single particle sources. We consider driving the dot out of equilibrium by a time-dependent bias voltage. We calculate the resulting current on the edge by applying the Kubo formula to the bosonized Hamiltonian. The Hamiltonian of this system can also be mapped to the spin-boson model and, in this picture, the current can be perturbatively calculated using the noninteracting blip approximation. We show that both methods of solution are in fact equivalent. We present numerics demonstrating that the perturbative approaches capture the essential physics at early times, although they fail to capture the charge quantization (or lack thereof) in the current pulses integrated over long times.
关键词： spin-boson model,quantum Hall edge,Laughlin state,quantum dot,noninteracting blip approximation,Kubo formula
更新于2025-09-11 14:15:04
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Counterpropagating continuous-variable entangled states in lossy coupled-cavity optical waveguides
摘要： We present an integrated source of counterpropagating entangled states based on a coupled resonator optical waveguide that is pumped by a classical pulsed source incident from above the waveguide. We investigate theoretically the generation and propagation of continuous-variable entangled states in this coupled-cavity system in the presence of intrinsic loss. Using a tight-binding approximation, we derive analytic time-dependent expressions for the number of photons in each cavity, as well as for the correlation variance between the photons in different pairs of cavities, to evaluate the degree of quantum entanglement. We also derive simple approximate expressions for these quantities that can be used to guide the design of such systems, and discuss how pumping configurations and physical properties of the system affect the photon statistics and the degree of quantum correlation.
关键词： quantum entanglement,lossy coupled-cavity optical waveguides,continuous-variable entangled states,counterpropagating,tight-binding approximation
更新于2025-09-11 14:15:04
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Theoretical calculation of optical absorption property of Cu@Ag core–shell composite nanoparticle
摘要： Because of their unique surface plasmon resonance (SPR) absorption in the visible region of the electromagnetic (EM) wavelength, plasmonic nanoparticles (NPs) such as gold (Au), silver (Ag) and copper (Cu) are utilized to combine with another material in devices. In this work, the optical absorption property exhibited by core–shell NPs composed of Cu cores with Ag shells (Cu@Ag) was investigated by the Discrete Dipole Approximation (DDA) method. In the theoretical calculation, at ?rst, the Ag shell thickness was ?xed at 5 nm and the Cu core diameters were varied between 10 and 30 nm. Second, the Cu core size was ?xed at 20 nm and the Ag shell thickness was varied from 2 nm to 10 nm. It was observed that as the size of the Cu core increased with a ?xed Ag shell thickness, the absorption peak gradually shifted to that of the pure Cu peaks (at ～358 nm and ～510 nm). On the other hand, the increasing Ag shell thickness showed the shifting of the absorption peak to the absorption peak of pure Ag NP (～432 nm). The results revealed that varying either the Cu core size or the Ag shell thickness could result in obtaining tuneable light absorption. Such typical nanomaterials are expected to ?nd application in future medical, solar cell and novel functional devices.
关键词： discrete dipole approximation,Cu@Ag core-shell,localized surface plasmon resonance
更新于2025-09-11 14:15:04
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Plasmon-pole approximation for many-body effects in extrinsic graphene
摘要： We develop the plasmon-pole approximation (PPA) theory for calculating the carrier self-energy of extrinsic graphene as a function of doping density within analytical approximations to the GW random phase approximation (GW -RPA). Our calculated self-energy shows excellent quantitative agreement with the corresponding full GW -RPA calculation results in spite of the simplicity of the PPA, establishing the general validity of the plasmon-pole approximation scheme. We also provide a comparison between the PPA and the hydrodynamic approximation in graphene, and comment on the experimental implications of our ?ndings.
关键词： plasmon-pole approximation,self-energy,graphene,GW-RPA,many-body effects
更新于2025-09-11 14:15:04
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[IEEE 2018 25th IEEE International Conference on Image Processing (ICIP) - Athens, Greece (2018.10.7-2018.10.10)] 2018 25th IEEE International Conference on Image Processing (ICIP) - Light Field Image Compression Based on Convolutional Neural Networks and Linear Approximation
摘要： Computer vision applications such as refocusing, segmentation and classification become one of the most advanced imaging services. LightField (LF) imaging systems provide a rich semantic information of the scene. Using a dense set of cameras and microlens arrays (Plenoptic camera), the direction of each ray coming from the scene toward the LF capture system can be extracted and represented by spatial and angular coordinates. However, such imaging system induces many drawbacks including the large amount of data produced and complexity increase for scene representation. In this paper, we propose an efficient LF image coding scheme. This scheme first encodes a sparse set of views using the latest hybrid video encoder (JEM). Then, it estimates a second sparse set of views using a linear approximation. At the decoder side, we use a Deep Learning (DL) approach to estimate the whole LF image from the reconstructed sparse sets of views. Experimental results show that the proposed scheme provides higher visual quality and overcomes the state of the art LF image compression solution by 30% bitrate gain.
关键词： LightField,MachineLearning,future video coding,Linear approximation,CNN
更新于2025-09-11 14:15:04
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Subtleties of witnessing quantum coherence in nonisolated systems
摘要： Identifying nonclassicality unambiguously and inexpensively is a long-standing open challenge in physics. The no-signaling-in-time protocol was developed as an experimental test for macroscopic realism, and serves as a witness of quantum coherence in isolated quantum systems by comparing the quantum state to its completely dephased counterpart. We show that it provides a lower bound on a certain resource-theoretic coherence monotone. We go on to generalize the protocol to the case where the system of interest is coupled to an environment. Depending on the manner of the generalization, the resulting witness either reports on system coherence alone, or on a disjunction of system coherence with either (i) the existence of nonclassical system-environment correlations or (ii) non-negligible dynamics in the environment. These are distinct failure modes of the Born approximation in nonisolated systems.
关键词： no-signaling-in-time protocol,macroscopic realism,quantum coherence,Born approximation,nonclassicality
更新于2025-09-10 09:29:36
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Effective dielectric tensor of deformed-helix ferroelectric liquid crystals with subwavelength pitch and large tilt angle
摘要： Short pitch deformed helix ferroelectric liquid crystals have numerous applications as active materials in displays, optical telemetry, and biomedical devices. In this paper, we derive convenient analytical formulas to calculate the effective dielectric tensor of these materials beyond the space average approximation. By comparison with exact numerical calculations, we show that our formulas are remarkably accurate in predicting optical properties in virtually all practical situations, including the important case of large tilt angles, where the space average approximation breaks down. We also present a comparison between the two complementary approaches of expanding the mesoscopic dielectric tensor versus the mesoscopic transfer matrix, by deriving an expression for the effective transfer matrix as an in?nite expansion and explicitly calculating the corresponding effective dielectric tensor for the ?rst time. Our results demonstrate that both methods give accurate predictions when two-photon scattering terms are taken into account.
关键词： deformed-helix ferroelectric liquid crystals,space average approximation,effective dielectric tensor,two-photon scattering,optical properties
更新于2025-09-10 09:29:36