Performance Improvement of Atmospheric Continuous-Variable Quantum Key Distribution with Untrusted Source

Atmospheric continuous-variable quantum key distribution (ACVQKD) has been proven to be secure theoretically with the assumption that the signal source is well protected by the sender so that it cannot be compromised. However, this assumption is quite unpractical in realistic quantum communication system. In this work, we investigate a practical situation in which the signal source is no longer protected by the legitimate parts, but is exposed to the untrusted atmospheric channel. We show that the performance of ACVQKD is reduced by removing the assumption, especially when putting the untrusted source at the middle of the channel. To improve the performance of the ACVQKD with the untrusted source, a non-Gaussian operation, called photon subtraction, is subsequently introduced. Numerical analysis shows that the performance of ACVQKD with an untrusted source can be improved by properly adopting the photon subtraction operation. Moreover, a special situation where the untrusted source is located in the middle of the atmospheric channel is also considered. Under direct reconciliation, we find that its performance can be significantly improved when the photon subtraction operation is manipulated by the sender.     

N2O处理对背沟刻蚀金属氧化物薄膜晶体管性能的影响

通过采用稀土元素镨掺杂铟锡锌氧化物半导体作为薄膜晶体管沟道层,成功实现了基于铝酸的湿法背沟道刻蚀薄膜晶体管的制备.研究了N₂O等离子体处理对薄膜晶体管背沟道界面的影响,对其处理功率和时间对器件性能的影响做了具体研究.结果表明,在一定的功率和时间处理下能获得良好的器件性能,所制备的器件具有良好的正向偏压热稳定性和光照条件下负向偏压热稳定性.高分辨透射电镜结果显示,该非晶结构的金属氧化物半导体材料可以有效抵抗铝酸的刻蚀,未发现明显的成分偏析现象.进一步的X射线光电能谱测试表明, N₂O等离子体处理能在界面处形成一个富氧、低载流子浓度的界面层.其一方面可以有效抵抗器件在沉积氧化硅钝化层时等离子体对背沟道的损伤;另一方面作为氢的钝化体,抑制了低能级施主态氢的产生,为低成本、高效的薄膜晶体管性能优化方式提供了重要参考.     

最优路径搜索压缩感知水声通信信道估计

将信号恢复中最优路径搜索的A*正交匹配追踪(A*Orthogonal Matching Pursuit,A*OMP)伪贪婪算法引入到水声通信信道估计中,可以有效改善正交匹配追踪(OMP)算法容易陷入局部最优的问题,并提出了一种改进型的A*OMP水声信道估计算法。改进了路径初始化方式,同时为了避免过多迭代引起的未知误差,将前后两次迭代残差之差作为停止准则。在正交频分复用(OFDM)通信体制下,对OMP、A*OMP和本文改进方法的估计误差和误比特率进行了仿真对比,随着信噪比的增加,改进方法未出现误差平台,且受导频间隔影响较小。仿真结果表明相对于OMP算法和传统A*OMP算法,在高信噪比下改进方法的估计误差分别降低约2和1个数量级,海试数据结果验证了改进方法的可行性,其误比特率分别平均降低42.0%和4.7%。     

Robustness of two-qubit and three-qubit states in correlated quantum channels

We investigate how the correlated actions of quantum channels affect the robustness of entangled states. We consider the Bell-like state and random two-qubit pure states in the correlated depolarizing, bit flip, bit-phase flip, and phase flip channels. It is found that the robustness of two-qubit pure states can be noticeably enhanced due to the correlations between consecutive actions of these noisy channels, and the Bell-like state is always the most robust one. We also consider the robustness of three-qubit pure states in correlated noisy channels. For the correlated bit flip and phase flip channels, the result shows that although the most robust and most fragile states are locally unitary equivalent, they exhibit different robustness in different correlated channels, and the effect of channel correlations on them is also significantly different. However, for the correlated depolarizing and bit-phase flip channels, the robustness of two special three-qubit pure states is exactly the same. Moreover, compared with the random three-qubit pure states, they are neither the most robust states nor the most fragile states.     

A prototype of quantum von Neumann architecture

A modern computer system, based on the von Neumann architecture, is a complicated system with several interactive modular parts. It requires a thorough understanding of the physics of information storage, processing, protection, readout, etc. Quantum computing, as the most generic usage of quantum information, follows a hybrid architecture so far, namely, quantum algorithms are stored and controlled classically, and mainly the executions of them are quantum, leading to the so-called quantum processing units. Such a quantum–classical hybrid is constrained by its classical ingredients, and cannot reveal the computational power of a fully quantum computer system as conceived from the beginning of the field. Recently, the nature of quantum information has been further recognized, such as the no-programming and no-control theorems, and the unifying understandings of quantum algorithms and computing models. As a result, in this work, we propose a model of a universal quantum computer system, the quantum version of the von Neumann architecture. It uses ebits (i.e. Bell states) as elements of the quantum memory unit, and qubits as elements of the quantum control unit and processing unit. As a digital quantum system, its global configurations can be viewed as tensor-network states. Its universality is proved by the capability to execute quantum algorithms based on a program composition scheme via a universal quantum gate teleportation. It is also protected by the uncertainty principle, the fundamental law of quantum information, making it quantum-secure and distinct from the classical case. In particular, we introduce a few variants of quantum circuits, including the tailed, nested, and topological ones, to characterize the roles of quantum memory and control, which could also be of independent interest in other contexts. In all, our primary study demonstrates the manifold power of quantum information and paves the way for the creation of quantum computer systems in the near future.     

闪电连续电流的光谱分析及通道温度特性研究

连续电流是闪电放电过程中的一个重要子物理过程,它是指雷暴云局部电荷中心在回击之后沿原通道对地的持续放电过程。在连续电流阶段,原本发光微弱的通道其亮度有时会突然增强,这种现象被称为叠加了M分量,自20世纪连续电流被发现以来,国内外学者进行了许多观测研究。目前主要是利用电磁学和光学的观测手段揭示其放电和发光的宏观特征,利用光谱观测对其通道内部微观的发光信息和物理特性等的研究还很缺乏。如关于连续电流阶段放电通道内的温度特性参数目前鲜有报道,而温度是研究闪电连续电流放电通道物理特性所必需的基本参量,也是预防连续电流引起的雷电灾害事故所关心的参数。依据由无狭缝高速光谱仪观测的一次云对地闪电首次回击后叠加三个M分量的连续电流过程的光谱资料,分析了整个放电过程中光谱的演化特征,计算了连续电流放电过程电流核心通道和外围电晕通道的温度,研究了两者随通道高度的变化特性。结果表明,在初始回击阶段,通道的光辐射主要是激发能较高的一次电离的氮离子辐射,在之后连续电流阶段,通道的光辐射则主要是激发能较低的中性氮、氧原子辐射。离子线辐射在回击初期时最强,氢Hα线和红外波段的中性原子线在M1时最强,连续谱在M2时最强。近红外波段的四条线OⅠ 777.4, NⅠ 746.8, 821.6和868.3 nm在整个放电过程都可以被观测到。在连续电流阶段,电流核心通道温度为42 060～43 940 K,比相应回击核心通道温度高6 020～7 900 K;外围电晕通道温度为16 170～20 500 K;通道核心温度和电晕温度均随时间变化不大;通道核心温度随通道上升呈减小趋势,而外围电晕温度随通道上升呈增大趋势。     

A threshold voltage analytical model for high-k gate dielectric MOSFETs with fully overlapped lightly doped drain structures

We investigate the influence of voltage drop across the lightly doped drain(LDD) region and the built-in potential on MOSFETs,and develop a threshold voltage model for high-k gate dielectric MOSFETs with fully overlapped LDD structures by solving the two-dimensional Poisson’s equation in the silicon and gate dielectric layers.The model can predict the fringing-induced barrier lowering effect and the short channel effect.It is also valid for non-LDD MOSFETs.Based on this model,the relationship between threshold voltage roll-off and three parameters,channel length,drain voltage and gate dielectric permittivity,is investigated.Compared with the non-LDD MOSFET,the LDD MOSFET depends slightly on channel length,drain voltage,and gate dielectric permittivity.The model is verified at the end of the paper.     

Effects of Relativistic and Ponderomotive Nonlinearities on an Intense Laser Pulse Propagation in a Plasma Channel

The optical guiding of a moderately intense laser pulse in a parabolic preformed plasma channel is analyzed by means of the variational method.Relativistic,ponderomotive and their coupling nonlinearities are included.The conditions for periodic defocusing and focusing,as well as constant spot size propagation are given.It is found that the laser focusing is released by the coupling of relativistic and ponderomotive nonlinearities.     

同轴场畸变气体火花开关的多通道放电特性

设计了一种同轴场畸变气体火花开关,在开关仅受触发脉冲作用和开关内外电极分别连接正负充电电容两种条件下,实验研究了触发脉冲峰值对开关间隙在氮气中的放电通道数的影响,比较了两种条件下的放电通道数。开关仅受触发脉冲作用时,放电通道承载电流较小;开关内外电极分别连接充电电容,触发脉冲施加于开关触发极时,放电通道承载电流较大。实验结果表明:仅受触发脉冲作用时,开关内间隙的平均通道数随着触发脉冲峰值增加而显著增加;开关电极连接电容的情况下,随着触发脉冲峰值增加,开关内间隙的平均通道数增加,外间隙的平均通道数减小;相近的过电压倍数下,开关电极连接电容情况下的平均通道数明显小于开关仅受触发脉冲作用情况下的平均通道数。     

The breakdown mechanism of a high-side pLDMOS based on a thin-layer silicon-on-insulator structure

A high-side thin-layer silicon-on-insulator (SOI) pLDMOS is proposed, adopting field implant (FI) and multiple field plate (MFP) technologies. The breakdown mechanisms of back gate (BG) turn-on, surface channel punch-through, and vertical and lateral avalanche breakdown are investigated by setting up analytical models, simulating related parameters and verifying experimentally. The device structure is optimized based on the above research. The shallow junction achieved through FI technology attenuates the BG effect, the optimized channel length eliminates the surface channel punch-through, the advised thickness of the buried oxide dispels the vertical avalanche breakdown, and the MFP technology avoids premature lateral avalanche breakdown by modulating the electric field distribution. Finally, for the first time, a 300 V high-side pLDMOS is experimentally realized on a 1.5 μ m thick thin-layer SOI.