Abstract
This paper presents an open-source package developed in Python that controls and drives a programmable Josephson array to synthesize dc and ac quantum-accurate voltages. Programmable arrays are devices subdivided into independent subsections, each counting a number of series connected Josephson junctions that follows a binary sequence (1, 2, 4, 8, …) to control the output voltage. Our software allows to independently measure the current-voltage characteristics of each subsection by means of a set of arbitrary waveform generators and a nanovoltmeter that measures the voltage across the whole array with high sensitivity. A quantization test tool is also provided to check with sub-microvolt resolution whether the array is operating on its quantum margins. The code is modular and easily expandable with the support of many libraries, allowing prompt reconfiguration for different calibration and testing purposes. It is aimed at being a starting point for cooperation between National Metrology Institutes towards the realization of a shared quantum voltage calibration infrastructure.
Highlights
The Josephson effect [1] is a macroscopic quantum phenomenon that occurs in devices made with two superconducting elements separated by a thin metallic or insulating layer
These are known as Josephson junctions and find application in many different research fields, from quantum voltage metrology to accurate magnetic flux measurements, from supercomputers to quantum information
Josephson junctions are operated under the irradiation of an rf-field: this high-frequency excitation causes the appearance of quantum voltage steps in the Josephson junction current-voltage characteristic (Fig 1), known as Shapiro steps [2], whose value is given by: nh VJ;n 1⁄4 2e frf ð1Þ
Summary
The Josephson effect [1] is a macroscopic quantum phenomenon that occurs in devices made with two superconducting elements separated by a thin metallic or insulating layer. Proprietary software is distributed as key component of such quantum-based voltage calibration systems: these are generally developed in LabView and are mostly oriented toward calibration activities rather than research needs, where a direct access to the source code is generally preferred. They typically provide the user with a wide variety of functions, as the check of the PJVS electrical characteristic, the automatic search of the optimal operating conditions (microwave power, bias currents) and the most accurate calibration of dc and ac voltages. The software is currently in its alpha-stage, the users are invited to cooperate with us in its further development and refinement: the source code is publicly available under GNU-GPLv3 license on GitHub [22]
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