我国的1V及10V约瑟夫森量子电压基准装置

文章描述了我国量子电压基准的建立、发展、现状和所取得的成果,以及与国际计量局进行基准关键比对的情况。     

我国的1V及10V约瑟夫森量子电压基准装置

文章描述了我国量子电压基准的建立、发展、现状和所取得的成果，以及与国际计量局进行基准关键比对的情况。     

Direct comparison between the NIST 10 V Conventional Josephson Voltage Standard and 2.5 V Programmable Josephson Voltage Standard

In the present paper, the intercomparison results of the NIST 10 V Conventional Josephson Voltage Standard (NIST10) and 2.5 V Programmable Josephson Voltage Standard (PJVS) Systems have been discussed. The two systems were directly intercompared at 1.018 V and 2.511 V from September 2006 to February 2007. The differences between the two systems (i.e. NIST10 — PJVS) at 1.018 V and 2.511 V were 0.21 nV and −0.95 nV respectively. The intercomparison results reveal that the noise of digital voltmeter (DVM) affects the measurement results significantly. Even with DVM of the same model, their noise rejection capability may be different when accuracy of a few nanovolt (nV) is required, although for Zener reference standard measurement, it is sufficient because the measurement uncertainty is dominated by the noise and non-linear drift of Zener reference standard.     

Direct comparison between the NIST 10 V Compact Josephson Voltage Standard and the 2.5 V Programmable Josephson Voltage Standard

The NIST 10 V Compact Josephson Voltage Standard (CJVS) and 2.5 V Programmable Josephson Voltage Standard (PJVS) were directly compared at 1.018 V and 2.511 V in February 2007. The difference between the two systems at 1.018 V (CJVS — PJVS) was −0.09 nV with an expanded uncertainty of 4.72 nV or a relative uncertainty of 4.64×10⁻⁹ at the 95 % confidence level where as the difference between the two systems at 2.511 V was 0.00 nV with an expanded uncertainty of 4.04 nV or a relative uncertainty of 1.61×10⁻⁹ at the 95 % confidence level. These intercomparison results demonstrated the satisfactory performance of the CJVS system handling minor trapped flux in the array and the effectiveness of the “NISTVolt software” to manage step jumps in the measurements.     

交流约瑟夫森电压标准系统的介绍

本文介绍了交流约瑟夫森电压标准系统的性能。该系统是一种新型的交流量子电压计量装置,用于校准常用的直流和交流电压标准。通过测试几个福禄克5700A系列校准器,其电压为10V,频率是1k Hz了解到该系统在工业环境中的性能和操作方法。交流电压标准的测量不确定度小于1×10-6     

10V约瑟夫森结阵电压基准

在 1V约瑟夫森结阵电压基准的基础上 ,10 V约瑟夫森结阵电压基准于 1999年底在中国计量科学研究院量子部电压实验室建立。其校准电压在 0 .1V～ 10 V范围内连续可调。校准固态电压标准 10 V输出值的合成不确定度为 5.4× 10 -9(1σ)     

1V脉冲驱动型交流量子电压源研究

脉冲驱动型交流量子电压标准ACJVS通过高速脉冲序列驱动约瑟夫森结阵芯片的方式实现宽频带交流量子电压的合成,相比于可编程型交流量子电压标准PJVS,具有免台阶切换、频谱纯净、频带宽等优点。搭建的系统主要包括8位高速脉冲码型发生器、微波放大器、直流阻断、约瑟夫森结阵芯片等。通过驱动包含4个子阵列,每个子阵列含12810个约瑟夫森结的结阵芯片,并结合4通道联合低频补偿的方式,成功产生了1V有效值的脉冲驱动型交流量子电压,为进一步建立交流量子电压基准打下了坚实的基础。最后,展望了脉冲驱动型交流量子电压在量子阻抗桥、交流量子功率源、交流量子功率表方面的应用价值。     

Recent NPL Work on the AC Josephson Effect as a Voltage Standard

The experimental equipment and procedure used in the latest National Physical Laboratory (NPL) ac Josephson effect determinations of 2e/h are described. The most recent value, obtained in April 1972, is 483 594.00 (±0.10) GHZ/VNPL and this, together with earlier results, provides information concerning the stability of the NPL maintained voltage standard over the past two years. To obtain a further increase in precision, new equipment is being developed for the measurements in which the resistive divider and null detector are maintained at cryogenic temperatures.     

An AC Josephson Voltage Standard for AC–DC Transfer-Standard Measurements

We describe the traceability chain of length measurements at Centre for Metrology and Accreditation (MIKES) from atomic clocks to the lasers of primary interferometers. Crucial part of the traceability chain, an optical frequency comb generator linking optical frequencies to atomic clocks, is described in detail. The frequency comb generator is used in frequency calibrations of iodine-stabilized lasers, which are operated in compliance with the recommendations of the practical realization of the definition of the meter. Measured absolute frequencies of iodine-stabilized lasers, time records of the measurements, and the respective Allan deviations demonstrate the solid performance of the MIKES laser frequency standards. The results are in good agreement with the recommended values, as well as with the independent characterizations of the measured lasers     

Systematic-Error Signals in the AC Josephson Voltage Standard: Measurement and Reduction

We investigate the dominant frequency-dependent systematic-error signals (SESs) in the AC Josephson voltage standard. We describe our error measurement technique and a number of methods to reduce the errors. Most importantly, we found that a small change in on-chip wiring significantly reduces the SES, improves SES measurement stability, and enables a suitable bias correction method. We show that direct analog-to-digital converter measurements of the SES of two on-chip Josephson arrays are in very good agreement with errors inferred from AC-DC transfer standard measurements. Finally, we demonstrate that the reduction of the SES using these techniques greatly improves the agreement between the AC-DC differences of the two arrays as well as the absolute AC voltage accuracy.     

First Direct Comparison of a Cryocooler-Based Josephson Voltage Standard System at 10 V

A commercially available and fully automated 10-V Josephson voltage standard system with a liquid helium free cooling has been developed as a result of the cooperation between the Institute of Photonic Technology and Supracon AG, both in Jena, Germany. The system operates with an array of 19 700 superconductor–insulator–superconductor Josephson tunnel junctions installed in a pulse tube cooler. A stable operation is achieved by the proper integration of the voltage standard circuit to the cold stage of the cryocooler. Different operation setups are discussed. A direct comparison of a cryocooler-based Josephson voltage standard system versus a liquid-helium-based system was performed at a voltage level of 10 V. We obtained a voltage difference of 1.3 nV with a total combined uncertainty of 2 nV. This corresponds to a relative uncertainty of $2 times 10^{-10}$.      

Correction of Systematic Errors Due to the Voltage Leads in an AC Josephson Voltage Standard

The National Institute of Standards and Technology (NIST) has recently reported the first application of a quantum ac Josephson voltage standard for the calibration of thermal transfer standards in the 1- to 10-kHz frequency range. This paper describes preliminary work on extending its frequency calibration range up to 100 kHz by correcting the systematic errors due to voltage leads. A ground loop created by the dc blocks, which is a previously unaccounted source of high-frequency systematic error, has been identified, and its effects are partially mitigated.      

AC–DC Transfer Standard Measurements and Generalized Compensation With the AC Josephson Voltage Standard

We present AC-DC transfer standard measurements using the National Institute of Standards and Technology's pulse-driven AC Josephson voltage standard source. We have investigated the frequency dependence for several output voltages up to 200 mV for frequencies from 2.5 to 100 kHz. We found that, as the frequency increases, the ac-dc differences for the two arrays on the same chip do not agree. We explored this deviation in ac-dc difference for the two arrays by investigating different configurations of the probe cabling and wiring, chip carriers, and on-chip circuit design. We found that the circuit design produced the greatest improvement, particularly at the highest frequency (100 kHz), where the deviation in ac-dc difference was reduced by more than 60%. In this paper, we also demonstrate tenfold higher output voltages and improved operating margins for arbitrary (nonsinusoidal) waveforms. These enhancements were accomplished by implementing a more general current bias to the arrays having the same harmonic content as that of the synthesized arbitrary waveform.     

Precision Differential Sampling Measurements of Low-Frequency Synthesized Sine Waves With an AC Programmable Josephson Voltage Standard

We have developed a precision technique to measure sine-wave sources with the use of a quantum-accurate ac programmable Josephson voltage standard. This paper describes a differential method that uses an integrating sampling voltmeter to precisely determine the amplitude and phase of high-purity and low-frequency (a few hundred hertz or less) sine-wave voltages. We have performed a variety of measurements to evaluate this differential technique. After averaging, the uncertainty obtained in the determination of the amplitude of a 1.2 V sine wave at 50 Hz is 0.3 $muhbox{V/V}$ (type A). Finally, we propose a dual-waveform approach for measuring two precision sine waves with the use of a single Josephson system. Currently, the National Institute of Standards and Technology (NIST) is developing a new calibration system for electrical power measurements based on this technique.      

Coupling of Josephson Radiation to Voltage Standard Arrays

We coupled the radiation emitted by arrays of Josephson junctions oscillators to detector arrays of small Josephson junctions. The number of junctions in the detector array ranges up to 1536, which is typical for a 1V standard array operation. Evidence is presented that both uniform coupling of the emitted radiation over all the small junctions arrays and coherent emission of the Josephson oscillators can be achieved. PACS numbers: 74.50. + r, 74.40. + k.     

Operating Margins for a Pulse-Driven Josephson Arbitrary Waveform Synthesizer Using a Ternary Bit-Stream Generator

We describe measurements with a pulse-driven Josephson arbitrary waveform synthesizer (JAWS) that uses a ternary arbitrary bit-stream generator as the bias source. This system is designed to be used as an ac Josephson voltage standard. From these measurements, we conclude that the system is operational for root-mean-square voltages of up to 220 mV. We measured the operating margins for different voltages synthesized with different numbers of junctions, waveforms, and bias conditions. We also present results on the influence of the critical current on the operating margins.      

A Two-Way Josephson Voltage Standard Comparison Between NIST and NRC

A two-way Josephson voltage standard (JVS) direct comparison between the National Institute of Standards and Technology (NIST) and the National Research Council (NRC) has been conducted. The process consists of two comparisons: first, using the NRC JVS with the NRC's measuring system (hardware and software) to measure the 10 V provided by the NIST JVS and then using the NIST JVS measuring system to measure the 10 V provided by the NRC JVS. The results of the two comparisons are in agreement to within 0.7 nV, and their mean indicates that the difference between the two JVSs at 10 V is $-$0.28 nV, with a pooled combined uncertainty of 2.07 nV $(k = 2)$ or a relative uncertainty of 2.1 parts in $10^{10}$.      

Development of a 60 Hz Power Standard Using SNS Programmable Josephson Voltage Standards

We are implementing a new standard for 60 Hz power measurements based on precision sinusoidal reference voltages from two independent programmable Josephson voltage standards (PJVS): one for voltage and one for current. The National Institute of Standards and Technology PJVS systems use series arrays of Josephson junctions to produce accurate quantum-based DC voltages. Using stepwise-approximation synthesis, the PJVS systems produce sinewaves with precisely calculable RMS voltage and spectral content. We present measurements and calculations that elucidate the sources of error in the RMS voltage that are intrinsic to the digital-synthesis technique and that are due to the finite rise times and transients that occur when switching between the discrete voltages. Our goal is to reduce all error sources and uncertainty contributions from the PJVS synthesized waveforms to a few parts in 10 ⁷ so that the overall uncertainty in the AC-power standard is a few parts in 10⁶     

Near-Zero Bias Arrays of Josephson Tunnel Junctions Providing Standard Voltages up to 1 V

Josephson voltage standards utilize microwave-induced constant voltage steps occurring due to the ac Josephson effect. Existing standards can be considerably simplified and their accuracy improved by using a large number of series-connected Josephson tunnel junctions which are operated in the zero current step mode. For this purpose superconducting millimeter wave integrated circuits have been designed, fabricated, and tested. The circuits consist of a broadband taper between the rectangular waveguide and the planar structure, the Josephson junction series, a well-matched load, and dc pads. Circuits with various numbers of junctions have been fabricated by photo-lithographic techniques and tested at 4.2 K in liquid helium. The version with 1474 junctions produced voltages up to 1.2 V when operated at 90 GHz.     

10V直流电压标准研究

本叙述了新型１０Ｖ直流电压标准的工作原理及系统组成，介绍了９：１哈蒙电压比较仪和高稳定恒流的研制方法，并分析了标准装置的测量不确定度。实验表明，该直流电压标准的合成标准不确定度为１．８＊１０＾－８。