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. 2018 Dec 17;13(12):e0209246.
doi: 10.1371/journal.pone.0209246. eCollection 2018.

A modular and customizable open-source package for quantum voltage standards operation and control

Paolo Durandetto  1   2 , Andrea Sosso  1
Affiliations

A modular and customizable open-source package for quantum voltage standards operation and control

Paolo Durandetto et al. PLoS One. .

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.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Ideal current to voltage characteristic of a Josephson junction under rf irradiation.
Quantized steps of order n = 0 and n = ±1 are clearly visible, along with their bias currents operating margins (blue shaded area).
Fig 2
Fig 2. Schematics of a PJVS binary-divided array.
A single Josephson junction is represented by ×. Each subsection is individually biased on its n = 0 or n = ±1 quantum step by adjusting the current Ii,n.
Fig 3
Fig 3. Circuital representation of the 13-bit PJVS system connected to fifteen independent AWG channels (Vin,i).
The blue shaded area shows the PJVS array and the rectangular boxes specify the number of junctions of each subsection. Ri is the output resistance of the ith AWG channel, which can be selected among 50 Ω, high impedance (open circuit) and low impedance (short circuit) in order to accomplish the desired operating mode.
Fig 4
Fig 4. Flow chart of the Python software for the PJVS controlled operation.
Fig 5
Fig 5. PJVS Waveform Synthesis GUI.
The graph displays the expected output waveform. On the right, the form for setting, saving and loading bias currents is shown.
Fig 6
Fig 6. PJVS IV-characteristics GUI.
The graph displays the averaged current-voltage characteristics of fourteen Josephson junctions subdivided in three consecutive sub-arrays.
Fig 7
Fig 7. PJVS Quantization Test GUI.
The two graphs display the voltage measurement and its running standard deviation.
See this image and copyright information in PMC

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