Elastic scattering is one of the useful methods to control the transmission behaviors of microwave photons transporting in microwave quantum networks without energy consumption.Therefore,it is of practical significance for developing microwave quantum devices and constructing multi-node microwave quantum networks.The transmission line embedded by a single Josephson junction can be described by different circuit models(series and parallel).In this work,we first theoretically analyze the transmission characteristics of microwave photons scattered by different elastic scattering models described by series or parallel embedding models,generated by a single LC loop or a nonlinear Josephson junction device,respectively.The classical microwave transport theory predicts that the series LC loop and the parallel LC loop lead to different elastic scattering behaviors of microwave photons,i.e.the series LC circuit yields the resonant reflection and the parallel LC circuit leads alternatively to the resonant transmission.Recently,the transport properties of microwave photons scattered by a Josephson junction embedded in a transmission line have been discussed,and the results suggested that the Josephson junction embedded in the transmission line can be described by a series embedding circuit,which implies the resonant reflection.We argue here that if the Josephson junction is embedded in parallel in the transmission line,the elastically scattered microwave photons should be transmitted by resonant transmission.In order to test which of the above two different embedding circuit models yielding the completely different elastic scattering behaviors,is physically correct,we then fabricate such a device,i.e.a single Joseph junction device embedded in a transmission line,and measure its elastic scattering transmission coefficient at an extremely low temperature.The results are consistent with the expected effect of the parallel embedding circuit model,but inconsistent with the behaviors predicted by the series embedding circuit model in the literature.According to the above theoretical and experimental analyses of the elastic scattering of a single Josephson junction device,we further propose a scheme to control the elastic scattering behavior of microwave photons by modulating a DC superconducting quantum interference device with a bypass current,which can be applied to the construction of a microwave quantum network based on elastic scattering node controls.

In this Letter, we experimentally demonstrated that Josephson threshold detectors (JTDs) could be developed to implement the sensitive detection of broadband microwave photons. Beginning with the numerical simulations of the damped dynamics for the macroscopic phase particle generated by a Josephson junction (JJ), we showed that the time-domain threshold voltage state switched measurements of the JJ driven by a low-frequency triangular wave current, which could be utilized to implement the sensitive microwave photons detection. The detectable signal power can be determined by using the Kumar–Caroll index to quantify the distinguishability between two statistical distributions on the measured threshold switched durations of the JJ with and without the signal input. Experimentally, we fabricated the Al/AlOx/Al JJ and measured its threshold responses, at 50 mK temperature, to the input microwave photons at the frequency of ∼5 GHz. The experimental results indicated that the weak microwave signals, which are phenomenologically threatened by the additional thermal noise that modifies the damped phase dynamics of the JJ, can be detected by the fabricated JTD. The detectable power of the microwave signals demonstrated here was calibrated as about −92 dBm (corresponding to the photons rate of ∼2×108 photons/ms). Based on the numerical simulations for optimizing the relevant performance indicators of the detectors, we further argue that the JTDs could be utilized to achieve the sensitive detection of broadband microwave photons at the single-photon level.

The electromagnetic induced transparency (EIT) to atomic systems and its various applications have been extensively investigated, both theoretically and experimentally. In this paper, we study how to similarly verify these phenomena in the waveguide coupled to the transmission line resonators. By making use of real space quantum scattering theory, we calculate the transmission spectrum of the waveguide photons scattered by a single quarter-wavelength transmission line resonator. Our experimental results show that the resonant microwave transporting along the feedline is completely reflected by the resonator. This is similar to the situation of the light absorbed by the resonant atomic medium, and thus its transmission is significantly suppressed.Like the EIT phenomena in atomic gas, wherein the resonant absorption can be significantly suppressed by applying a strong pumping light to control the optical properties of medium, the transport properties of the resonant microwave can be investigated by coupling it into an auxiliary quarter-wavelength resonator in this paper. If the frequency of the auxiliary quarter-wavelength resonator is different from the resonant frequency, the calculated transmission spectrum shows that the coupling with auxiliary quarter-wavelength resonator induces the complete transmission of the resonant microwave. This is one of the features of the EIT-like effect, and can be simply explained as the frequency renormalization of the coupling resonators. Also, by adjusting the coupling strength between the resonators, the width of the microwave transmission spectrum window can be manipulated. Our experimental observations verify such an argument, but the phase shift mutation (another typical signs of the EIT effect) of the resonant microwave cannot be observed. In physics, this is because the interference between the transmitted microwave and the reflected micowave with different frequencies does not take place in the coupling region between the two resonators.It is expected that the effects with the complete EIT-like phenomena can be observed, in future, by fabricating the sample of two quarter-wavelength transmission line resonators with the same frequency, and thus the coupling between the two resonators can be controlled.

The accurate time-frequency (TF) positioning of power quality (PQ) disturbances is the basis of dealing with PQ problems in power systems. To accurately detect PQ disturbances, this article proposes a Kaiser window-based S-transform (KST) that provides better time resolution at fundamental frequency to detect the amplitude information for voltage swell, sag, interrupt, flicker, and better frequency resolution at higher frequencies to detect the frequency of time-varying harmonics and oscillatory transient. Based on short-time Fourier transform and S-transform, KST uses a Kaiser window with the characteristic of inherent optimal energy concentration as the kernel function. The Kaiser window can be adjusted adaptively according to the detection demand of PQ disturbances by the designed control function. This allows KST to easily accommodate different detection requirements at different frequencies. The utilization of Fourier transform ensures that KST can be realized quickly. The complex TF matrix is generated after a signal is transformed by KST, where the column vector is expressed as the distribution of amplitude and phase with time at a certain frequency, and the row vector represents the distribution of amplitude and phase with frequency at a certain sampling time. Experimental results demonstrate that the proposed KST significantly outperforms the state-of-the-art techniques in TF analysis of PQ signals, especially for the energy concentration and the detection of fundamental wave.

近年来,研发以直接调控量子系统波函数本身为主要标志的第二代量子技术,如原子钟和量子信息技术(主要包括量子通信、量子计算机和量子传感)等受到了国际学术界和产业界的极大关注.其中,实现微弱电磁信号物理极限检测的单光子探测器是实现光量子信息处理必不可少的关键器件.面向量子信息处理的应用,本文介绍单光子探测的基本原理及单光子探测器主要的性能指标,系统总结在光量子信息处理研究中发挥重要作用的超导单光子探测器近20年来的研究进展,并对推动未来微波量子信息处理研究的微波单光子态探测器的发展前景进行展望.

Renewable energy sources will be more vigorously deployed under the global trend of carbon emission reduction. The connection of numerous renewable energy sources poses an increasingly critical challenge to power quality (PQ) issues in power systems. Time-frequency analysis (TFA) is a foundational technique for real-time monitoring and disturbance detection for power signals. This paper develops an improved S-transform (IST) to accurately detect the disturbances such as oscillatory transient, time-varying harmonics and interharmonics, flicker, swell, sag, interrupt, phase jump, and frequency variation. The proposed IST features the exploration of a designed Gaussian window as the kernel function, whose shape and frequency spectrum can be controlled using a standard deviation based detection frequency parameter. This ensures that the detection requirements at different detection frequencies can be easily met. The IST can be realized by fast Fourier transform (FFT) and its inverse, which ensures that it can be implemented quickly. The IST can accurately detect the amplitude and phase information of fundamental signal, which is beneficial to determine the start and end time, and the intensity of disturbance. With the increase of detection frequency, IST also has excellent energy concentration performance. Simulation and experimental results validated the effectiveness and feasibility of the proposed method.

The determination of uranium in environmental samples has always been a crucial environmental issue due to its adverse impacts on human life. Electrochemical detection is one of the most suitable methods for directly determining uranium because of its portable instrument and quick response characteristics. The ion-selective membrane in the working electrodes is selectively responsible for uranium transport and separation. This mini-review provides a general overview of the membrane-based ion-selective electrodes in detecting uranium ions reported in the literature. The ion-selective membranes are classified according to their ionophore categories. Furthermore, the limits and outlook are also discussed to provide a reference for further developing membrane-based electrochemical uranium sensors.

为了对未知脉冲所含的光子数进行标定,针对不同光子数的光脉冲在超导环境下,微波动态电感探测器(MKID)作用时,测量系统输出的信号差异性,采用平均区间取值法和迭代法分别进行标定,并进行了理论分析和实验验证.结果表明,MKID能够在低温测量系统中对未知1550nm单脉冲光的光子数进行识别;经过数据处理后得到平均光子数分别为1.98和1.81;其中平均区间取值法标定光子数过程较为简单,迭代法有待继续探索.这一结果对单脉冲光子数检测是有帮助的.

If the electromagnetic waves are scattered by the periodic structure of media with different refractive indexes, a band gap in the transmitted spectrum can be generated. This is the photonic crystal whose band gap is usually uncontrollable as its structure parameters are fixed after the fabrication. Alternatively, based on the quantum theory in real space for single photons transporting along a one-dimensional waveguide embed by a series of two-level atoms, we propose here a quantum mechanical configuration to implement the photonic crystal with adjustable band gap. It is shown that if the scattering two-level atoms are arranged as a periodic array, the desirable band gap in the photonic transmission spectrum can be formed. This is the atomic-type photonic crystal, in which the center frequency of the gap can be controlled by adjusting the eigenfrequencies of the atoms. The possible physical implementations of our proposal with the voltage-biased superconducting qubits for the centimeter waves and the voltage-biased electrons on liquid helium for the millimeter waves are also discussed.

Power divider is a useful device that divides the power of signal into different subpowers at a certain ratio. The superconducting power divider plays an important role in various superconducting quantum computing circuits and superconducting microwave photon detectors. Therefore, in this paper we investigate how to design and prepare a typical coplanar waveguide superconducting microwave power divider. The parameters are designed by using the odd-even mode method to analyze the transport features of a three-port microwave network. Specifically, the microwave transport properties of the device with a center frequency of 5 GHz and 3 dB power division ratio are simulated. Then, the designed aluminum coplanar waveguide superconducting power divider on silicon is prepared by micro-processing technology and experimentally tested at low temperature. It is shown that the measurement results are consistent with the design parameters. It is noted that the center frequency of the actually prepared power divider is measured to be about 5.25 GHz, which is slightly different from the result of the design and simulation. This difference is probably due to the following main reasons. Firstly, the limited precision of the micromachining process is caused by the fact that the fabricated quarter-wave impedance matching line is etched incompletely, leading the length of the impedance matching line to be shortened. As a consequence, the frequency of the prepared power divider is slightly higher. Secondly, the simulation software is not designed specially for superconducting device simulations, thereby yielding the design parameters slightly different from those of the fabricated superconducting devices. Additionally, a series of attenuations has been used in the experimental test system of the superconducting microwave power dividers for reducing the various noises. This causes the input test signal to weaken, thus the reflected signal turns significantly small. Therefore, none of the S11 parameters of the device can be effectively measured. Finally, neither of S21 and S31 parameters measured in the experiment is the predicted –3 dB, which is mainly due to the imperfections in the welding between SMA connectors and high-frequency transmission lines, and the spot welding between high-frequency transmission lines and power divider samples, and also due to the discontinuities of the high-frequency transmission line and the power divider and so on. All these factors can yield the tested insertion loss of the device. Hopefully, the method in this work can be extended to designing and preparing other passive superconducting microwave devices.

It has been nearly 110 years since the discovery of superconductors, and more than 30 years since the discovery of high temperature superconductors (HTS). Great progress has been made in the application of superconducting electronics in the last two decades. HTS microwave devices have shown much higher perfomance than the traditional ones and have found their ways to the industry applications in mobile communication, radar, and special communication applications. Owing to the ultrahigh sensitivity to magnetic fields and currents, superconducting quantum interference devices (SQUIDs) have been used as the irresplacible sensors in geological surveying, magnetic resonanc imaging, biomagnetic imaging, and other areas. The sensitivity of superconducting radiation detectors such as superconducting SIS mixer, superconducting hot electron bolometer, superconducting transition edge sensor, superconducting nanowire single photon detector, and superconducting microwave kinetic inductance detector are near the quantum limitation. They are now key technology in geophysics, astrophysics, quantum information science, biomedicine, and so on. Superconducting Josephson parametric amplifier has become a key element for superconducting quantum computing. Superconducting integrated circuit has been included in the international roadmap for devices and systems, and shows that having the potential to become one of the mainstreams for post-Moore information processing technology. In metrology, superconducting Josephson effect and Josephson junction array devices have been widely used in the redefinition of quantum voltage reference and basic units of the International system of Units. Superconducting electronics plays an important role in the current quantum information technology boom, which in turn promotes the development of superconducting electronics. This review will brief introduce the research and application of superconducting electronics in China in recent years.

Noise is one of the main factors affecting the performance index of weak signal detection devices, and the optimal filtering algorithm is an effective method to adaptively extract various useful weak signals from the white noise background. In order to improve the performance of single photon detector (especially the photon number resolution ability), one mainly focuses on the optimization of detector hardware such as the optimization of photosensitive materials and the technology of device fabrication. However, in this paper the performance of microwave kinetic Inductance detector (MKID) in the way of data processing is improved. Considering the fact that the template of light pulse signal in the optimal filtering algorithm is obtained by taking the average, we replace the noise model in the original optimal filtering algorithm with the white noise model and the whitening noise model. Then we process the photon response data that are detected by the MKID in an extremely low temperature environment. The results show that the energy resolution (one of the main performance indexes of single photon detector) of MKID is improved by about 15%, and we achieve an infrared single photon energy resolution of 0.26 eV. In this paper, the application and development trends of superconducting single photon detector are briefed. Then, how the MKID responds to weak coherent optical signal in low temperature environment, and the process of signal conversion, acquisition and output are explained in detail. According to the optimal filtering algorithm, we use different noise models to analyze the results of the signals detected by MKID. After that, we count the optimal amplitude multiple, perform the Gaussian fitting analysis on the statistical graph, and compare the energy resolution with the photon number resolution of the optimal filtering algorithm under different noise models. As a result, we find that under the white noise model, the optimal filtering algorithm is used to obtain the best result for MKID processing, and high energy resolution can be achieved.

The ac-dc difference of the ac-dc transfer standard fluke 792A has been calibrated at millivolt voltage in this paper. The 792A is calibrated based on the voltage divider techniques. A cascaded inductive voltage divider (IVD) has been built with using binary inductive voltage dividers (BIVDs) in cascade connection. The ratio errors of the cascaded IVD are calibrated against the self-calibrated BIVD at millivolt voltages. A resistive voltage divider (RVD) which has equal ratio with the cascaded IVD has also been built. The dc and ac ratio errors at low frequencies are consistent. The VDs can trace the small voltages to the thermal voltage converter (TVC) and be used to measure the ac-dc difference of the 792A at mV ranges.

This paper describes an online smart meter calculating method by analysis the smart meter consumption data. In this model, orthogonal matching pursuit algorithm and decision tree are applied to detect abnormal data and cluster data. Then a submeter matrix is constructed to compute meter error. The experiment shows the validity and effectiveness of this meter error estimation method.

This paper describes the application of a microvolt Josephson voltage standard based on a dual-channel Josephson junction array developed at NIM. Using the microvolt Josephson voltage standard, DC voltage measurements ranging from 1 μV to 20 μV have been realized. And two different types of nanovoltmeters have been calibrated for non-linearity on 6 μV and 20 μV ranges. Results have demonstrated that the latest developed microvolt Josephson voltage standard is practical and can meet the requirement of low-level DC measurements.

Smart meter has been considered as the key element in the smart grid and current smart meter verification method failed to coverage all deployed meters. Online calibration for is a novel approach which calculate meter error by analysing meter reading data. This paper presents a comprehensive survey and basic model of smart meter online calibration and proposed a recursive algorithm to estimate meter error. Concrete steps have been illustrated and testing case shows the higher accuracy of the method. Finally, some issues of online calibration in application were discussed.

A modified generalized S transform is designed to extract the parameters of power quality disturbances such as starting and ending time, amplitude, harmonic frequencies more accurately in this paper. The demands of power quality detection is better met by controlling the Gaussian window function. Finally, the simulation results show that the excellent time-frequency performance of this method.

Detecting inaccurate smart meters and targeting them for replacement can save significant resources. For this purpose, a novel deeplearning method was developed based on long short-term memory (LSTM) and a modified convolutional neural network (CNN) to predict electricity usage trajectories based on historical data. From the significant difference between the predicted trajectory and the observed one, the meters that cannot measure electricity accurately are located. In a case study, a proof of principle is demonstrated for detecting inaccurate meters with high accuracy for practical usage to prevent unnecessary replacement and increase the service lifespan of smart meters.

This paper describes how to trace the ultra-low frequency voltage to the dc voltage standard at frequency ranges from 0.1 Hz to 10 Hz. An ultra-low frequency ac-dc transfer system is developed with using dual-heater thermal voltage converter (TVC). The dual-heater TVC can output stable thermoelectric potential when inputting two quadrature low-frequency voltages with equal amplitude. The key parameters in the ultra-low frequency ac-dc transfer system have been evaluated to make the dual-heater TVC output stable thermoelectric potential.