G. Geneves

The BNM Watt balance project

A new watt balance project is now developed by the BNM: the general configuration and the main parts of the experimental set-up in development are presented. Its aim is to contribute to the international effort in monitoring the kilogram towards a new definition of the mass unit with an accuracy of 10-8 or better

Report on a joint BIPM-EUROMET project for the fabrication of QHE samples by the LEP

The quantum Hall effect (QHE) samples fabricated by LEP according to specifications intended to optimize their usefulness in metrology are described. Their measured characteristics, notably carrier density, carrier mobility at zero magnetic field, dependence of the quantized resistance on temperature, measuring current, and the quality of electrical contacts, are reported. >

Micro-gravity investigations for the LNE watt balance project

We report on a micro-gravity survey of the laboratories where the LNEs watt balance experiment is being conducted, including the characterization of the Scintrex CG-5 relative gravimeter used for this study. The results of the survey are compared with a model of the gravity field generated by the local mass distribution. The ultimate goal is to transfer an absolute measurement of g from one room to another with minimal uncertainty.

Characterization of diode detectors used in six-port reflectometers

A method for characterizing in situ the diodes used as power detectors in six-port network analyzers is presented. The method requires only two unknown loads which are connected at the measurement ports. Measurement results obtained for one-port and two-port devices with a dual six-port realized in the 2-18-GHz frequency range are reported. In order to show the influence of frequency, these results are compared to those obtained using a midband characterization of the diode detectors. >

Magnetic circuit design for the BNM Watt balance experiment

BNM has started since 2001 the development of a watt balance experiment. The authors present in this paper the design of the magnetic circuit intended to equip it

First determination of the Planck constant using the LNE watt balance

After separate developments of the different elements with continuous characterizations and improvements, the LNE watt balance has been assembled. This paper describes the system in detail and gives its first measurements of the Plancks constant h. The value determined in air is h = 6.626 068 8(20) × 10−34 Js which differs in relative terms by −0.05 × 10−7 from the h90 value and by −1.1 × 10−7 from that of the 2010 CODATA adjustment of h. The relative standard uncertainty associated is 3.1 × 10−7.

A first attempt to realize (multiple-QHE devices)-series array resistance standards

Several chips composed of ten quantum Hall effect (QHE) devices placed in series by triple connections have been fabricated. The results obtained on one of these first arrays of quantized Hall resistances (QHR) open the possibility to realize novel QHR standards. The QHR on the i=2 plateau, 10/spl times/R/sub H/(i=2), was compared to R/sub H/(i=2) from a standard type QHE sample acting as a reference. The comparison results agreed to within parts in 10/sup 9/ for the measurements of a 1000 /spl Omega/ standard resistance. This work followed preliminary tests on the multiple connection techniques. In particular, the QHR on the i=2 plateau of a special QHE sample allowing the auto-series configuration with a double connection was found equal to 2/spl times/R/sub H/(i=2) within the total standard uncertainty of 4.4 parts in 10/sup 9/.

Quantum resistance standards with double 2DEG

A new generation of quantum Hall array resistance standards (QHARS) designed from GaAs/AlGaAs heterostructures with double two-dimensional electron gases (2DEGs) has been developed. First results of measurements carried out on a single Hall bar (R/sub K//4) and 50 Hall bars placed in parallel by triple connections (R/sub K//200) are presented.

Volume magnetic susceptibility of gold–platinum alloys: possible materials to make mass standards for the watt balance experiment

In 2000, the Bureau National de Metrologie (BNM, France) decided to develop a new watt balance experiment. Among numerous design studies, the choice of the transfer mass is particularly important. Because of the proximity to a source of high magnetic intensity, this mass must have a magnetic susceptibility as weak as possible. Gold–platinum alloy seems to meet this requirement, as well as additional requirements for density and hardness values, making it a possible candidate for mass standard realization. Five different gold–platinum alloys were studied, their volume magnetic susceptibility ranging from −2.8×10−5 to −2.1×10−5 for two of them and from +1.1×10−5 to +8.8×10−5 for the other three.

AC measurements of the minimum longitudinal resistance of a QHE sample from 10 Hz to 10 kHz

AC measurements of the longitudinal resistance, R/sub xx/, of a quantum Hall effect (QHE) sample have been made in a frequency range from 10 Hz to 10 kHz. The results show no frequency effect on the minimum value of R/sub xx/ corresponding to the quantum numbers i=2 and i=4, within the measurement resolution of 0.5 m/spl Omega/. Therefore, the influence of frequency on the value of the quantized Hall resistance, R/sub H/, should not exceed a few parts in 10/sup 9/. Some unwanted effects detected during the development of the resistance bridge have been pointed out.