319 research outputs found
Development of Josephson voltage standards
Neurology & clinical neurophysiolog
Chapter Development of Josephson voltage standards
Neurology & clinical neurophysiolog
Programmierbare Josephson-Arrays für Impedanzmessungen
An innovative way of networking two programmable Josephson arrays generating synchronous waveforms for impedance ratio measurements, as the first of its kind, is presented. This pioneering approach of the Josephson Impedance Bridges is far more flexible than conventional bridges at the same level of measurement uncertainty. Results prove that aside from having the capability of measuring
over a wider frequency range, the Josephson bridge permits measurements on two impedances with any value of phase angle between them. In the two-terminal-pair Josephson bridge setup, measurements are made for a 1:1 resistance ratio at the 10-k level in the frequency range between 25 Hz and 10 kHz. Uncertainties reach to levels of better than a few parts in 108 and results agree to the values measured from conventional impedance bridges.
Two methods for four-terminal impedance measurements have been investigated, the potential comparison circuit and the coaxial setup. Both methods are capable of measuring from DC to 6 kHz with uncertainties to 10−8. The four-terminal-pair coaxial setup has potential to decrease the relative uncertainty down to 10−9 once systematic errors are analyzed and canceled. Thermal converter measurements have been made to investigate the effects of transients on stepwise approximated sinewaves. Rms measurements show that transients limit the uncertainty to about 10−6 at 1 kHz. A simple model with an equivalent time constant is presented to evaluate the influence of different parameters on the shape of the transients. It has been experimentally established, at the 10−8 level of uncertainty for the determination of impedance ratios, that the variations of the transients in stepwise approximated waveforms can be neglected when using the fundamental component of rectangular waveforms. Quantization at up to 10 kHz has been confirmed by varying the bias current of the Josephson arrays resulting in constant resistance ratios within the measurement resolution.Ein innovativer Weg, zwei programmierbare Josephson-Schaltungen für Impedanz-Verhältnismessungen zu verknüpfen, wird erstmals in dieser Arbeit präsentiert. Dieser neuartige Ansatz einer Josephson-Impedanzmessbrücke ist flexibler als konventionelle Impedanzmessbrücken bei gleicher Messunsicherheit. Es wird gezeigt, dass neben der Möglichkeit, über einen wesentlich größeren Frequenzbereich zu messen, die Josephson-Impedanzmessbrücke auch Messungen sehr unterschiedlicher Impedanzverhältnisse und beliebiger Phasenwinkel erlaubt. In einer Zwei-Tor-Anordnung der Josephson-Impedanzmessbrücke wurden Messungen für ein 1:1 Widerstandsverhältnis bei 10 k im Frequenzbereich von 25 Hz bis 10 kHz durchgeführt. Die Ergebnisse stimmen mit denen einer konventionellen Messbrücke im Rahmen der Unsicherheit von wenigen 10−8 überein.
Für eine Vier-Tor-Anordnung wurden zwei unterschiedliche Methoden untersucht, eine Spannungsverhältnisschaltung und eine koaxiale Vier-Tor-Anordnung. Letztere hat das Potential, Unsicherheiten von 10−9 zu erreichen, sobald systematische Fehler eliminiert sind.
Um Effekte der Transienten in stufenförmig approximierten Sinuswellen zu untersuchen, wurden Messungen an Thermokonvertern durchgeführt. Diese Effektivmessungen zeigen, dass Transienten die relative Messunsicherheiten auf etwa 10−6 bei einer Frequenz von 1 kHz beschränken. Es wird ein einfaches Modell vorgestellt, das die Form der Transienten in Abhängigkeit der wesentlichen Parameter beschreibt. Experimentell konnte bei Impedanzverhältnismessungen mit einer relativen Messunsicherheit von 10−8 nachgewiesen werden, dass die Variation der Transienten in stufenförmig approximierten Wellenformen vernachlässigbar ist, wenn die fundamentale Komponente eines Rechtecksignals verwendet wird. Quantisierte Plateaus wurden bis zu Frequenzen von 10 kHz gefunden, bei denen die Variation des angelegten Stroms durch die Josephson-Schaltungen keine Veränderung des Impedanzverhältnisses zur Folge hatte
Analogue to Digital and Digital to Analogue Converters (ADCs and DACs): A Review Update
This is a review paper updated from that presented for CAS 2004. Essentially,
since then, commercial components have continued to extend their performance
boundaries but the basic building blocks and the techniques for choosing the
best device and implementing it in a design have not changed. Analogue to
digital and digital to analogue converters are crucial components in the
continued drive to replace analogue circuitry with more controllable and less
costly digital processing. This paper discusses the technologies available to
perform in the likely measurement and control applications that arise within
accelerators. It covers much of the terminology and 'specmanship' together with
an application-oriented analysis of the realisable performance of the various
types. Finally, some hints and warnings on system integration problems are
given.Comment: 15 pages, contribution to the 2014 CAS - CERN Accelerator School:
Power Converters, Baden, Switzerland, 7-14 May 201
Readout and Control Beyond a Few Qubits: Scaling-up Solid State Quantum Systems
Quantum entanglement and superposition, in addition to revealing interesting physics in their own right, can be harnessed as computational resources in a machine, enabling a range of algorithms for classically intractable problems. In recent years, experiments with small numbers of qubits have been demonstrated in a range of solid-state systems, but this is far from the numbers required to realise a useful quantum computer. In addition to the qubits themselves, quantum operation requires a host of classical electronics for control and readout, and current techniques used in few-qubit systems are not scalable. This thesis presents a series of techniques for control and readout of solid-state qubits, working towards scalability by integrating classical control with the quantum technology. Two techniques for reducing the footprint associated with readout of gallium arsenide spin qubits are demonstrated. Gate electrodes, used to define the quantum dot, are also shown to be sensitive state detectors. These gate-sensors, and the more conventional Quantum Point Contacts, are then multiplexed in the frequency domain, where three-channel qubit readout and ten-channel QPC readout are demonstrated. Two types of superconducting devices are also explored. The loss in superconducting coplanar waveguide resonators is measured, and a suppression of coupling to the parasitic electromagnetic environment is demonstrated. The thesis also details software for the simulation of Josephson-junction based circuits including features beyond what is available in commercial products. Finally, an architecture for managing control of a scalable machine is proposed where classical components are distributed throughout a cryostat and cryogenic switches route control pulses to the appropriate qubits. A simple implementation of the architecture is demonstrated that incorporates a double quantum dot, a gallium arsenide switch matrix, frequency multiplexed readout, and cryogenic classical computation
Investigating the feasibility of using nanobridge weak links as the active Josephson element in Rapid Single Flux quantum circuitry
Josephson junctions are used in present day voltage standards. To extend their use to AC voltage standards a high bandwidth, low-noise detector is required. A candidate component for this detector is a superconducting comparator based on Rapid Single Flux Quantum (RSFQ) circuits. The work presented here is a study to determine if nanobridge weak links can be used as the active Josephson element in these circuits. In order to achieve this an understanding of the nanobridge properties and in particular their critical currents is fundamental. We present simulations of a simple comparator using the circuit simulation software JSIM in order to study the effect of varying nanobridge parameters such as width, length, and loop area. These geometrical variables have an affect on the critical currents and loop inductances which subsequently effect device performance. Particular emphasis is given to investigation of how these parameters affect a key figure of merit, the grey zone width
Second year technical report on-board processing for future satellite communications systems
Advanced baseband and microwave switching techniques for large domestic communications satellites operating in the 30/20 GHz frequency bands are discussed. The nominal baseband processor throughput is one million packets per second (1.6 Gb/s) from one thousand T1 carrier rate customer premises terminals. A frequency reuse factor of sixteen is assumed by using 16 spot antenna beams with the same 100 MHz bandwidth per beam and a modulation with a one b/s per Hz bandwidth efficiency. Eight of the beams are fixed on major metropolitan areas and eight are scanning beams which periodically cover the remainder of the U.S. under dynamic control. User signals are regenerated (demodulated/remodulated) and message packages are reformatted on board. Frequency division multiple access and time division multiplex are employed on the uplinks and downlinks, respectively, for terminals within the coverage area and dwell interval of a scanning beam. Link establishment and packet routing protocols are defined. Also described is a detailed design of a separate 100 x 100 microwave switch capable of handling nonregenerated signals occupying the remaining 2.4 GHz bandwidth with 60 dB of isolation, at an estimated weight and power consumption of approximately 400 kg and 100 W, respectively
The ampere and the electrical units in the quantum era
By fixing two fundamental constants from quantum mechanics, the Planck
constant and the elementary charge , the revised Syst\`eme International
(SI) of units endorses explicitly quantum mechanics. This evolution also
highlights the importance of this theory which underpins the most accurate
realization of the units. From 20 May 2019, the new definitions of the kilogram
and of the ampere, based on fixed values of and respectively, will
particularly impact the electrical metrology. The Josephson effect (JE) and the
quantum Hall effect (QHE), used to maintain voltage and resistance standards
with unprecedented reproducibility since 1990, will henceforth provide
realizations of the volt and the ohm without the uncertainties inherited from
the older electromechanical definitions. More broadly, the revised SI will
sustain the exploitation of quantum effects to realize electrical units, to the
benefit of end-users. Here, we review the state-of-the-art of these standards
and discuss further applications and perspectives.Comment: 78 pages, 35 figure
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