Development of a PJVS System for Quantum-Based Sampled Power Measurements

The paper deals with recent progresses at INRiM towards the development and characterization of a programmable Josephson voltage standard (PJVS) operating in a small liquid helium dewar as well as with its integration for the realization of a practical quantum sampling electrical power standard. The PJVS is based on a 1V superconductor-normal metal-superconductor (SNS) binary-divided array of 8192 Josephson junctions. To ensure proper operating conditions of the PJVS chip, a custom short cryoprobe was designed, built and successfully tested. The overall system is being developed in the framework of EMPIR project 19RPT01-QuantumPower. The goal is to establish a new quantum power standard (QPS) based on a single Josephson voltage standard for sampled power measurements and to gain confidence in running PJVS for precise calibration of digital sampling multimeters and arbitrary waveform digitizers used in the ac-voltage and power metrology community

Non-Conventional PJVS Exploiting First and Second Steps to Reduce Junctions and Bias Lines

Quantum digital-to-analog converters (DACs) based on programmable Josephson array [Programmable Josephson Voltage Standard (PJVS)] represent the most widely used quantum standard in ac voltage calibrations. The extension of PJVS frequency above the kilohertz range appears to be arduous; however, some enhancements are still practicable. In this work, we demonstrate the possibility to advantageously operate a conventional binary-divided PJVS array with a reduced number of bias lines. This feature is achieved by exploiting both the first and the second Shapiro steps along with nonconventional DAC codings. Two newly devised bias techniques are described in detail and preliminary experimental tests on waveform synthesis have been carried out and are presented here

Characterization of a Josephson array for pulse-driven voltage standard in a cryocooler

partially_open6sìPulse-driven Josephson junctions allow the synthesis of very precise both spectrally pure and arbitrary wave forms with frequencies up to the megahertz range. We investigated the properties relevant for metrological applications of series arrays with 4000 Josephson junctions fabricated at PTB in cryocooler and liquid helium. DC electrical parameters were evaluated and Shapiro steps dependence on operating conditions was studied. Both cooling techniques provided similar results for all relevant parameters. In particular, we were able to observe Shapiro step widths of more than 1 mA in cryocooler. Yet, we found that some specific effects related to the different thermal conditions must be taken into account for proper operation in cryocooler.openSosso, A.; Durandetto, P.; Trinchera, B.; Kieler, O.; Behr, R.; Kohlmann, J.Sosso, A.; Durandetto, P.; Trinchera, B.; Kieler, O.; Behr, R.; Kohlmann, J

A scalable readout system for a superconducting adiabatic quantum optimization system

We have designed, fabricated and tested an XY-addressable readout system that is specifically tailored for the reading of superconducting flux qubits in an integrated circuit that could enable adiabatic quantum optimization. In such a system, the flux qubits only need to be read at the end of an adiabatic evolution when quantum mechanical tunneling has been suppressed, thus simplifying many aspects of the readout process. The readout architecture for an $N$-qubit adiabatic quantum optimization system comprises $N$ hysteretic dc SQUIDs and $N$ rf SQUID latches controlled by $2\sqrt{N} + 2$ bias lines. The latching elements are coupled to the qubits and the dc SQUIDs are then coupled to the latching elements. This readout scheme provides two key advantages: First, the latching elements provide exceptional flux sensitivity that significantly exceeds what may be achieved by directly coupling the flux qubits to the dc SQUIDs using a practical mutual inductance. Second, the states of the latching elements are robust against the influence of ac currents generated by the switching of the hysteretic dc SQUIDs, thus allowing one to interrogate the latching elements repeatedly so as to mitigate the effects of stochastic switching of the dc SQUIDs. We demonstrate that it is possible to achieve single qubit read error rates of $<10^{-6}$ with this readout scheme. We have characterized the system-level performance of a 128-qubit readout system and have measured a readout error probability of $8\times10^{-5}$ in the presence of optimal latching element bias conditions.Comment: Updated for clarity, final versio

Practical quantum realization of the ampere from the electron charge

One major change of the future revision of the International System of Units (SI) is a new definition of the ampere based on the elementary charge \emph{e}. Replacing the former definition based on Amp\`ere's force law will allow one to fully benefit from quantum physics to realize the ampere. However, a quantum realization of the ampere from \emph{e}, accurate to within $10^{-8}$ in relative value and fulfilling traceability needs, is still missing despite many efforts have been spent for the development of single-electron tunneling devices. Starting again with Ohm's law, applied here in a quantum circuit combining the quantum Hall resistance and Josephson voltage standards with a superconducting cryogenic amplifier, we report on a practical and universal programmable quantum current generator. We demonstrate that currents generated in the milliampere range are quantized in terms of $ef_\mathrm{J}$ ($f_\mathrm{J}$ is the Josephson frequency) with a measurement uncertainty of $10^{-8}$. This new quantum current source, able to deliver such accurate currents down to the microampere range, can greatly improve the current measurement traceability, as demonstrated with the calibrations of digital ammeters. Beyond, it opens the way to further developments in metrology and in fundamental physics, such as a quantum multimeter or new accurate comparisons to single electron pumps.Comment: 15 pages, 4 figure

Chapter Development of Josephson voltage standards

Neurology & clinical neurophysiolog

Development of Josephson voltage standards

Neurology & clinical neurophysiolog