An ac quantum voltmeter based on a 10 V programmable Josephson array that is simple to use, provides dc and ac calibration up to kHz range for equipment widely used in metrology, and ensures direct traceability to a quantum-based standard, is developed. This ac quantum voltmeter is proven to match conventional Josephson standard systems at dc and extends its advantages up to 10 kHz in the low-frequency ac range. The ac quantum voltmeter is capable of performing calibrations up to 7 V RMS in the frequency range from dc to 10 kHz completely under software control. A direct comparison at dc has demonstrated an uncertainty better than 2 parts in 10 10 (k = 2). The uncertainty at 1 kHz is better than 1.7 µV V −1 (k = 2) for a measurement time of 1 min. The ac quantum voltmeter is a robust and practical system that fulfils the needs of general metrology laboratories for quantum-based voltage calibrations.

This paper describes the development of an automated ac quantum voltmeter toward a turnkey system, which can be used for calibration of common dc and ac voltage standards. The setup was tested in an accredited commercial calibration laboratory to characterize Fluke 5700A calibrators and voltage standards. The measured voltage in dependence on various parameters is presented in the range of dc to 2 kHz with amplitudes up to 10 V. The uncertainty components are discussed, and the system relevant Type B uncertainty for ac voltage calibrations is 0.15 µV/V. The contribution of the leakage current is investigated in detail and found to be notable for frequencies above 1 kHz due to parasitic capacitances. The combined measurement uncertainty for calibration ac voltages is less than 0.62 µV/V (k = 1 and 40 Hz-1 kHz) and is limited by the noise of the calibrator. Comparison measurements at Physikalisch-Technische Bundesanstalt have been done and confirm the system reproducibility.Index Terms-AC Josephson metrology, ac quantum voltmeter, calibration, calibrator Fluke 5700A, Josephson voltage standard, programmable Josephson voltage standard (PJVS).

To measure the noise performance of highly sensitive SQUID magnetometer systems directly is nearly impossible due to superimposed external noise. In magnetically unshielded environments in particular one needs sophisticated methods in order to get an estimate of the intrinsic noise. We compare different approaches to estimate the noise of our latest SQUID magnetometer systems in the Earth's magnetic field and compare the results with measurements in magnetic (and superconductive) shielding.

We present the concept and experimental set-up of a passive submillimeter-wave stand-off imaging system for security applications. Our ambition is the design of an application-ready and user-friendly camera providing high sensitivity and high spatial resolution at video frame rates. As an intermediate step towards this goal, the current prototype already achieves a frame rate of 10 frames per second and a spatial resolution below 2 cm at 8 m distance. The camera is the result of a continuous development and a unique concept that yielded first high-resolution passive submillimeter-wave images provided by cryogenic sensors in May et al. (2007). It is based on an array of 20 superconducting transition-edge sensors operated at a temperature of 450 mK, a closed-cycle cooling system, a Cassegrain-type optics with a 50 cm main mirror, and an opto-mechanical scanner. Its outstanding features are the scanning solution allowing for high frame rates and the compact and integrated system design.

Geophysical exploration is getting more and more difficult—many of the easily explorable ore-bodies have been discovered and are already being exploited. Finding new mines requires new technologies and tools. Transient electromagnetics (TEM) is widely used in mineral exploration, but conventional sensors (especially induction coils) cannot fulfil the needs anymore: deep targets, very conductive targets or targets under conductive overburden are more easily (or sometimes only) detected using SQUIDs. In this paper we will focus on low temperature SQUID magnetometers. As the systems are applied worldwide it is necessary to strengthen them for all conceivable application scenarios. Here, we report on the latest development of these systems which are now routinely used in South Africa, Australia, Finland and Canada. This paper highlights the main features of the system and describes one example from mineral exploration.