Appearance of Spatial-Temporal Noise in Super-conducting Junction and Its Effect on Transport of Electron Pairs

Transport of electron pairs in super-conducting junction with spatial-temporal noise is investigated. We show that the spatial-temporal noise can produce the current of the electron pairs, which stems from a symmetry breaking of the system induced by the correlation of the spatial-temporal noise with the phase difference. It is found that there is a positive current for the electron pairs, exhibiting a peak with increasing the values of some parameters of the noises. The results provide a theoretical foundation for the further investigation of the super-conducting junction.     

Net Voltage and Phenomenon of Resonance Induced by Chaotic Signal for a Superconducting Junctions Device

The effects of a quenched chaotic signal on the over-damped motion of the electron pairs of a superconducting junctions device are studied. It is shown that the chaotic signal can induce the net voltage and the phenomenon of resonance.     

Giant-Resonance for a Four-Dimensionally Coupled System with Dichotomous Noise

In this paper, we investigate a four-dimensionally coupled system driven by dichotomous noise. A new kind of stochastic resonance is found, for which the response of the system to the input signal can be hugely intensified.     

Frequency （Stochastic） Resonance and Stochastic Resonance for a Superconducting Junctions＇ Device

In this paper, we investigate a Josephson-junction device with dichotomous resistance or a special SQUID （superconducting quantum interference device）. It is shown that frequency （stochastic） resonance and stochastic reso- nance can appear for some suitably selected parameters＇ values of the device respectively. Our results can provide some insights for the investigation of the SQUID response to the signal （including the input alternating current, the added al- ternating voltage, the vertically added alternating magnetic field, and the detected （electric-magnetic） temporal-periodic signal）.     

全铌超导Josephson结的EWB仿真模型

通过超低温实验直接测量了制备的全铌Josephson结的电压源驱动RCSJ模型的I-V特性曲线。建立了Josephson结在电路仿真软件EWB中的模型,极大的方便了Josephson结及相关电路的仿真研究。利用这一新模型对Josephson结的基本特性进行了较为系统的研究,包括RSJ模型和RCSJ模型的直流驱动I-V特性曲线。     

Photon-Assisted Electron Transport for a λ-shaped Carbon Nanotube Junction

We theoretically study the electron transport properties for two coupled single-walled caxbon nanotube quantum dots connected to metallic electrodes under the irradiation of an external electromagnetic field at low tempera- tures. Using the standaxd nonequilibrium Green＇s function techniques, we examine the time-averaged transmission coefficient and linear conductance. It is shown that by some numerical examples, the photon-assisted inter-dot coupling causes Fano resonance and the conductance of the system is sensitive to the external field parameters. The transport dependence on the external field parameters may be used to detect the high-frequency microwave irradiation.     

Bosonic Operator Realization of Hamiltonian for a Superconducting Quantum Interference Device

Based on the appropriate bosonic phase operator diagonalized in the entangled state representation we construct the Hamiltonian operator model for a superconducting quantum interference device. The current operator and voltage operator equations are derived.     

微波与热偏置下超导HEB太赫兹直接检测器的性能比较

本文介绍了一种基于超导氮化铌(NbN)热电子测辐射热计(HEB)的太赫兹(THz)直接检测器,并利用直流读出法和微波反射读出法,对微波与热偏置下HEB直接检测器的性能进行了比较.通过直流读出法,在最佳工作点处,测得微波偏置与热偏置条件下检测器的电流响应率分别为244A/W和20A/W,光学噪声等效功率(NEP)分别为4.5pW/√Hz和6.8pW/√Hz.相比于热偏置,微波偏置能够大大提高检测器的响应率.此外,我们利用微波反射读出法对微波偏置和热偏置下检测器的性能进行了比较.两种读出方式均可很好的表征检测器的性能,而相比于直流读出法,微波反射读出法更易于扩展到多像素阵列,同时具有很快的读出速度,对快速THz脉冲信号的检测具有重要意义.     

Unconventional Geometric Phase Gate with Superconducting Quantum Interference Device Qubits in Cavity QED

In the system with superconducting quantum interference devices （SQUID） in cavity, a scheme for constructing two-qubit quantum phase gate via a conventional geometric phase-shift is proposed by using a quantized cavity field and classical microwave pulses. In this scheme, the gate operation is realized in the subspace spanned by the two lower flux states of the SQUID system mud the population operator of the excited state has no effect on it. Thus the effect of decoherence caused from the levels of the SQUID system is possible to minimize. Under cavity decay, our strictly numerical simulation shows that it is also possible to realize the unconventional geometric phase gate. The experimental feasibility is discussed in detail.     

The potential of the superconductor-vacuum-superconductor junction as a mixing element at submillimetre wavelengths

By removing the solid insulator in the superconductor-insulator-superconductor junction and making use instead of the vacuum as the tunnelling medium it should be possible to reduce the junction capacitance by a factor of about ten. This would facilitate the development of tunnelling receivers for submillimetre wavelengths by making it possible to fabricate junctions of normal size with electrical properties appropriate for high-frequency operation.     

SiC电子输运特性的Monte Carlo数值模拟

利用系综MonteCarlo法研究了2H ,4H和6HSiC的电子输运特性.在模拟中考虑了对其输运过程有着重要影响的声学声子形变势散射、极化光学声子散射、谷间声子散射、电离杂质散射以及中性杂质散射.通过计算,获得了低场下这几种不同SiC多型电子迁移率同温度的关系,并以4H SiC为例,重点分析了中性杂质散射的影响.最后对高场下电子漂移速度的稳态和瞬态变化规律进行了研究.将模拟结果同已有的实验数据进行了比较,发现当阶跃电场强度为10×106V·cm-1时,4H Sic电子横向瞬态速度峰值接近33×107cm·s^-1,6H Sic接近30×107cm·s^-1.     

硅纳米结点电子输运性质的计算

运用第一性原理密度泛函理论结合非平衡格林函数方法,对3个Si原子构成的直线链耦合在Au(100)面形成的三明治结构的纳米结点的电子输运进行计算.结果得到结点电导随距离的变化,当d_z=1.584 nm时,结合能最小,结构最稳定,此时Si-Si键长为0.216 nm,Si-Au键长为0.227 nm,电导为0.729 G₀(G₀=2e²/h),其电子传输通道主要由Si原子的p_x、p_y轨道电子构成;随着外电压的增大,结点的电导减小,而其I-V曲线表现出线性特征.     

HIRFL—CSR实验环电子冷却装置调试

HIRFL-CSR实验环电子冷却装置采用了能够产生空心电子束的电子枪。弯曲螺线管内采用了静电偏转电极，冷却段采用了独立的高精度螺线管串联产生纵向磁场的设计。测量了沿离子束运动方向冷却段磁场分布及磁场平行度、电子枪和收集器性能、300kV高压电源相关参数。结果表明，此装置达到了预期的设计目标。: In CSRe electron cooling device， a special electron gun which can produce variable profile electron beam with different size and density distribution was adopted for decreasing ion losses. Electrostatic bending device was used for reducing electron beam losses and improving vacuum condition. The instability of the electron beam is suppressed because the secondary electrons from collector would come back to the collector in the same orbit finally. Longitudinal magnetic field with parallelism better than 10-4 was achieved by adopting of independent high precise solenoid coils at cooling section. In this case， the r.m.s deviations of the transverse magnetic field at cooling section in horizontal and vertical direction are 3.298×10-5 and 2.458×10-5 respectively. The characters of the gun and collector were investigated. The results were presented and indicate that it achieves the design purpose very well.     

1.3GHz新结构超导实用单胞腔物理设计

报道了一个新设计的单胞腔,其表面电场峰值与加速梯度之比值E_p/E_acc小于1.8.把它做为9胞腔的半端胞时,其中间胞π模的E_p/E_acc可以低到2.024,胞-胞间耦合系数k可高达1.95%.并用阻带模型计算了单胞腔的高次模特性;阐述了超导驻波腔腔形的概念、腔几何参数定义、腔胞和束管设计原则、加速模和高次模计算方法,并讨论了程序计算的可靠性条件.     

Quantum Nonlocality of Photon Pairs in Interference in a Mach-Zehnder Interferometer

Nonlocal character of entangled photon pairs generated in spontaneous parametric downconversion is demonstrated. One photon from a pair propagates through a Mach-Zehnder interferometer and is detected in coincidence-count measurement with its twin. Width of the coincidence-count interference pattern (measured for various values of path difference in the Mach-Zehnder interferometer) depends on spectral width of the twin as a result of entanglement of photons in a pair. The experimental setup is analyzed for a Gaussian spectral filter and a Fabry-Perot resonator. It is shown that nonlocal interference is much stronger for cw pumping in comparison with femtosecond pulsed pumping for values of parameters commonly used in spontaneous parametric downconversion experiments.     

吸收材料对超导高频腔高次模抑制的实验研究

束流粒子通过加速腔的基模加速,以达到所需的能量值. 由于腔本身的多谐性,束流在超导腔里面会激发起高次模,其中其电场分布对粒子加速起到负面作用的,称之谓有害高次模,减小或抑制有害高次模是加速腔研究的一个重要环节,利用铝模型腔对超导腔的高次模抑制进行研究,给出测量结果,研究表明:铁氧体是很好的微波吸收材料,对于所研究的超导腔内的高次模有着良好的吸收效果.     

Study of Properties in Superconducting Nanowires

We consider a simple approach of standard Ginzburg--Landau free-energy functional for a wire to study the properties of superconducting nanowires, and analyze the problem of quantum and thermally activated phase slips. In such systems one can consider a possibility for phase slips to be created not only due to thermal but also due to quantum fluctuations of a uperconducting order parameter. We obtain some expressions of the free energy, the entropy, the specific heat and the bias current, respectively. The bias current I is a function of the temperature and the length of superconducting nanowires, and has a quantum phase slip. We obtain the stochastic dynamics of superconductive-resistive switching in hysteretic current-biased superconducting nanowires undergoing phase-slip fluctuations, and obtain the distribution of switching currents. Our results can be verified in modern experiments with superconducting nanowires.     

Nonequilibrium Electron Transport Through a Quantum Dot from Kubo Formula

Based on the Kubo formula for an electron tunneling junction, we revisit the nonequilibrium transport properties through a quantum dot. Since the Fermi level of the quantum dot is set by the conduction electrons of the leads, we calculate the electron current from the left side by assuming the quantum dot coupled to the right lead as another side of the tunneling junction, and the other way round is used to calculate the current from the right side. By symmetrizing these two currents, an effective local density states on the dot can be obtained, and is discussed at high and low temperatures, respectively.