Global optimization design of quasi-optics fower combiner of solid-state millimeter wave resonator

This paper describes a global optimization design of quasi-optics power combiner of solid-state millimeterwave resonator. It is operated in the frequency range from 50 to 300 GHz using GaAs Gunn diodes. It is shown that sourcearrays containing N² (N=3,5,...2K+1, where k is positive integer) individual elements. It is very efficient power transfer of energy from the source-array to the fractional power of the fundamental beam mode etc.. The RF output power exceeded the sum of the individual diodes to be threefold to sevenfold. And this data is the global optimization solution.     

Beam steering correction of the quarter wave resonator in the HISCL

The Intensity Heavy Ion Superconducting Linear Accelerator as the injector of the High Intensity Heavy-Ion Accelerator Facility, which is a new project proposed in China has been designed. One of the design options in the low energy part is based on Quarter Wave Resonators (QWRs). However, because of the unsymmetrical geometry of the cavity, there are dipole fields near the beam hole, which may steer the beam vertically, thus leading to emittance growth and beam loss. The effect of the dipole mode field is analyzed, and a method to overcome the beam steering effect by placing QWRs with opposite orientation is proposed in this paper. The simulation results show that the beam steering effect is reduced effectively by this method, and the deviation of the beam centroid is decreased from 2.87 mm to 0.1 mm. The emittance growth is also smaller.     

改进铜铌溅射型QWR超导腔性能的探讨

通过直流偏压二级溅射方法，在无氧铜腔体表面溅射一层铌膜，研制了铜铌溅射型射频超导1/4波长谐振腔(quarter wave resonator,QWR)，该腔主要用于重离子的加速，是北京放射性核束装置中后加速部分的预研项目.目前国际上很多实验室都在研究进一步提高铜铌溅射型QWR超导腔的性能，通过多种方法的实验研究，发现在无氧铜衬底与铌膜之间加入一层氮 化铌（NbN）薄膜，可以使得表面铌膜的超导温度转变点由原来的8.8K提高到了接近9.6K ，该方法有可能成为提高QWR腔加速性能的重要途径，目前进一步研究正 关键词： 溅射 QWR超导腔 氮化铌NbN 超导温度     

Compact superconducting single-and dual-band filter design using multimode stepped-impedance resonator

This study presents two multimode stepped-impedance structures to design single-and dual-band filters. Transmission zeroes are introduced for the single-band filter by using dual-mode stepped-impedance resonators. The single-band filter with high selectivity is centered at 6.02 GHz and has a fractional bandwidth(FBW) of 25.6%. Four stubs(two low frequency and two high frequency ones) are connected to the rectangular patch in the center to construct a quadruplemode resonator. The independent conditions of the center frequencies of the high and low bands of the resonator are analyzed. A dual-band filter, which operates at 1.53 GHz and 2.44 GHz with FWBs of 12.1% and 14.1%, respectively is designed. The single-and dual-band filters are both fabricated with double-sided YBCO films and they can be used in mobile and satellite communications.     

Electromagnetic wave generation in a cylindrical resonator by electrons orbiting in a radial electrostatic field

The mechanisms leading to the generation of microwaves by electrons orbiting in a radial electrostatic field produced by a positively charged filament on the axis of a cylindrical resonator are investigated theoretically. The dispersion relations describing the interaction of the waves with the electrons are obtained. It is shown that the generation of electromagnetic fields is possible on account of both Cherenkov and plasma resonances. The frequencies and growth rates of waves under Cherenkov resonance conditions and also plasma resonance conditions in uniform and nonuniform electron layers are found. The advantages and disadvantages of different generation mechanisms are determined. Zh. Tekh. Fiz. 68, 91–94 (August 1998)     

Design of a superconducting low beta niobium resonator

The proposed high current injector for the superconducting Linac at the Inter-University Accelerator Centre will have several accelerating structures, including a superconducting module which will contain low beta niobium resonators. A prototype resonator for the low beta module has been designed. The resonator has been carefully modelled to optimize the electromagnetic parameters. In order to validate them, a room-temperature copper model has been built and tested. In this paper we present details of the electromagnetic design of the low beta resonator, briefly discuss the mechanical and engineering design, and present results from the measurements on the room-temperature copper model.     

Phase-locking transition in a chirped superconducting Josephson resonator

We observe a sharp threshold for dynamic phase locking in a high-Q transmission line resonator embedded with a Josephson tunnel junction, and driven with a purely ac, chirped microwave signal. When the drive amplitude is below a critical value, which depends on the chirp rate and is sensitive to the junction critical current I0, the resonator is only excited near its linear resonance frequency. For a larger amplitude, the resonator phase locks to the chirped drive and its amplitude grows until a deterministic maximum is reached. Near threshold, the oscillator evolves smoothly in one of two diverging trajectories, providing a way to discriminate small changes in I0 with a nonswitching detector, with potential applications in quantum state measurement.     

Preliminary design and multipacting simulation of a SRF quarter wave electron gun at Peking University

Peking University is designing a new SRF gun that is composed of a quarter wave resonator (QWR) and an elliptical cavity. Compared to the elliptical cavity, the QWR is sufficiently compact at the same frequency and its electric field is quasi-DC. The RF parameters are determined by optimization of QWR cavity structure and the possible multipacting locations are analyzed by 2D MP simulation. The simulation results show that multipacting is not a critical issue for our optimized cavity structure.     

Preliminary design and multipacting simulation of a SRF quarter wave electron gun at Peking University

Peking University is designing a new SRF gun that is composed of a quarter wave resonator （QWR） and an elliptical cavity. Compared to the elliptical cavity, the QWR is sufficiently compact at the same frequency and its electric field is quasi-DC. The RF parameters are determined by optimization of QWR cavity structure and the possible multipacting locations are analyzed by 2D MP simulation. The simulation results show that multipacting is not a critical issue for our optimized cavity structure.     

Strong coupling of a spin ensemble to a superconducting resonator

We report the realization of a quantum circuit in which an ensemble of electronic spins is coupled to a frequency tunable superconducting resonator. The spins are nitrogen-vacancy centers in a diamond crystal. The achievement of strong coupling is manifested by the appearance of a vacuum Rabi splitting in the transmission spectrum of the resonator when its frequency is tuned through the nitrogen-vacancy center electron spin resonance.     

Geometry dependent multipacting of a superconducting quarter-wave resonator at PKU

A superconducting quarter-wave resonator (QWR) of frequency=162.5 MHz and β=0.085 (β =v/c) has been designed at Peking University. The multipacting (MP) simulation and analysis for the QWR with CST Particle Studio has been performed. The simulation results reveal that there is no sign of MP with its normal operating accelerating gradients in the range of 6-8 MV/m. The accelerating gradient range that may incur MP is from about 1.4 to 3.2 MV/m, and the places where MP may be encountered are mainly located at the top part of the QWR. So the effect of different top geometries on MP has also been studied in depth. Our results show that an inward convex round roof is better than other round roofs, and plane roofs have an advantage over round roofs on the suppression of MP in general. While considering the optimization of its electromagnetic (EM) design, our initial designed model is also acceptable.     

Integrated superconducting circuit for qubit and resonator protection

A semi-infinite waveguide acts as a mirror and helps protect the qubit in front of it from decoherence. Here, we investigate the interference effect in an open waveguide consisting of resonators with different decay rates. We find that a lossy resonator works as a mirror and changes the effective decay rate of the other. The spontaneous radiation of qubit is related to its environment, and we can control it by arranging the lossy resonator's position or frequency. Our approach helps improving the qubit performance, as well as the quantum gate fidelities.     

Coupling and readout of semiconductor quantum dots with a superconducting microwave resonator

In a circuit quantum electrodynamics(circuit QED) architecture, the microwave resonator could be used to couple and probe qubits. The long-range coupling and information transfer between nonlocal qubits can be performed via photons trapped in a microwave resonator, promising an effective approach for scaling up solid-state qubits. A series of important advances in the hybrid system composed of a microwave resonator and semiconductor qubits have been achieved in recent years. For instance,with ap...     

High-contrast dispersive readout of a superconducting flux qubit using a nonlinear resonator

We demonstrate high-contrast state detection of a superconducting flux qubit. Detection is realized by probing the microwave transmission of a nonlinear resonator, based on a SQUID. Depending on the driving strength of the resonator, the detector can be operated in the monostable or the bistable mode. The bistable operation combines high-sensitivity with intrinsic latching. The measured contrast of Rabi oscillations is as high as 87%; of the missing 13%, only 3% of the loss of contrast is unaccounted for. Experiments involving two consecutive detection pulses are consistent with preparation of the qubit state by the first measurement.     

使用改进的形状优化方法设计高均匀度的超导MRI磁体

针对设计带铁磁的超导磁共振成像磁体,提出了一种确定类的优化算法来优化极靴的形状以达到匀场的目的。这种方法集合了灵敏度分析、形状优化的理论和有限元方法计算非线性铁磁材料极靴的配置,来改善两个极靴之间大体积成像区的磁场均匀度。需要指出的是,本优化方法不受极靴初始形状的限制,均可以快速收敛。我们通过一个紧凑型的1.2T双平面磁共振磁体,展示了这种方法。     

Non-Markovian entanglement transfer to distant atoms in a coupled superconducting resonator

We investigate the non-Markovian effects on the entanglement transfer to the distant non-interacting atom qubits,which are embedded in a coupled superconducting resonator. The master equation governing the dynamics of the system is derived by the non-Markovian quantum state diffusion(NMQSD) method. Based on the solution, we show that the memory effect of the environment can lead to higher entanglement revival and make the entanglement last for a longer time. That is to say, the non-Markovian environment can enhance the entanglement transfer. It is also found that the maximum entanglement transferred to distant atoms can be modified by appropriately selecting the frequency of the modulated intercavity coupling. Moreover, with the initial anti-correlated state, the entanglement between the cavity fields can be almost completely transferred to the separated atoms. Lastly, we show that the memory effect has a significant impact on the generation of entanglement from the initial non-entangled states.     

Controllable microwave frequency comb generation in a tunable superconducting coplanar-waveguide resonator

Frequency combs are useful in a wide range of applications,such as optical metrology and high-precision spec-troscopy.We experimentally study a controllable fre...     

粒子群算法改进及在高温超导磁体优化设计中的应用

本文阐述了基本粒子群优化方法及其改进,选用测试函数对该算法及其改进算法的寻优性能作了对比;并利用Comsol软件对单螺线管超导储能磁体进行了电磁计算,阐述了磁场垂直分量最大值的位置及高温超导磁体的磁场垂直分量对临界电流的影响;最后将各种优化方法应用于高温超导磁体的设计中。经联合仿真优化,高温超导磁体减小了体积,提高了材料利用率,节约了材料用量,并减小了制冷时所消耗的电源功率。     

一种三柱式超导电抗器的概念设计

无功平衡对提高电网的经济效益和改善供电质量至关重要。目前用于电网无功补偿的传统电抗器难以实现无级调节,容量较小,或装置控制复杂,有较严重的谐波,难以在高电压等级的电网中大规模应用。为了解决高压电网的无功缺额问题,研究了一种三柱式的超导电抗器。文章介绍了该超导电抗器的工作原理,阐述了超导电抗器的设计方法。按照设计方法,对35kV电压等级的超导电抗器进行设计;在理论设计的基础上,采用有限元方法对理论设计进行优化,完成概念设计。仿真结果表明,该三柱式超导电抗器有较好的无功调节性能;该概念设计为高压大容量超导电抗器的研制提供了一定的参考依据。