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Conference on Precision Electromagnetic Measurements

Biasing Josephson Junctions with Optoelectronically Generated Pulses

Jonathan M. J. Williams, L. Palafox, David A. Humphreys, T. J. B. M. Janssen

Published Jun 1, 2004• 6 citations
Publisher

Abstract

A new way of biasing an array of Josephson junctions using optoelectronically generated pulses is described. This method facilitates the generation of positive and negative electrical pulses needed for bipolar waveform synthesis and provides an easy way of optimising the array bias using variable optical attenuators
DOI
10.1109/cpem.2004.305468

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A new method of driving series arrays of non-hysteretic Josephson junctions using optoelectronically generated pulses to synthesize a variable output voltage is described. Electrical pulses from a photodiode are coupled to the array, and the mean output voltage after filtering is proportional to the pulse repetition frequency with fundamental accuracy. Numerical simulations of the behaviour of the Josephson junctions have been carried out, and these results have been verified by experiment. This technique can be easily extended by using two photodiodes with opposite bias polarities in order to synthesize bipolar alternating or direct voltages.
An array of Josephson junctions (JJs) was driven with photonically generated current pulses to synthesize a high-fidelity 1 kHz bipolar voltage waveform with a quantum-based amplitude that can be directly related to fundamental constants. A photodiode capable of producing high average photocurrent was used to generate large-amplitude current pulses that were ac-coupled to a JJ array. The resulting bipolar current pulses have enabled the first demonstration of quantum-based bipolar waveform synthesis with an optical drive. We measured the quantum locking range with respect to several operating parameters, including 1.2 mA with respect to a dc bias current applied to the array, confirming the robust synthesis of bipolar waveforms.
Pulse-driven Josephson voltage standards are used to generate quantum-based, spectrally pure AC voltage signals. The current pulses that drive the Josephson arrays can be transmitted optically and recent progress has demonstrated the operation of fast photodiodes at 4 K. In order to generate bipolar waveforms, two photodiodes are required to generate positive and negative pulses close to the Josephson array. We describe our optoelectronic setup and will present first results on a ternary pulse drive at the conference.
After demonstrating bipolar waveforms in 2020, PTB’s optical pulse transmission drive has been expanded for two independent Josephson junction arrays. Passive optical power splitters divide the two independent optical channels at room temperature. Balanced photodiodes modules in liquid helium then generate ternary electrical pulses to drive the nearby Josephson junction arrays via coplanar waveguides less than 10 mm long. The outputs of the Josephson junction arrays are connected in series and we successfully synthesized bipolar sinewaves at 1 kHz and 35 mV rms amplitude with higher harmonics suppressed by more than 96 dBc.
Abstract We have successfully operated two Josephson junction arrays in parallel with photonically generated current pulses to achieve higher output voltages with our optical pulse drive setup. Passive optical power splitters divide each optical channel at room temperature in order to illuminate multiple cryogenic photodiodes at 4 K , located near the arrays. The balanced photodiode configurations bias the Josephson junctions with ternary current pulses to generate a 1 kHz bipolar sinusoidal voltage with a nominal root mean square amplitude of 85 mV . We determined a spurious free dynamic range and total harmonic distortion of 110.6 dBc and − 105.0 dB from the spectrum of the synthesized signal. Applying an additional dither current to each array individually yielded a quantum locking range of 0.4 mA and 0.6 mA . Furthermore, the quantum locked operation was confirmed to remain stable when the optical output power of the laser diodes and the DC bias of the Mach–Zehnder modulators were varied. A stability measurement of the output amplitude over more than half an hour confirmed sufficiently wide operating margins, further demonstrating a reliable optical Josephson arbitrary waveform synthesizer setup suitable for generating quantum-based waveform with high spectral purity traceable to fundamental constants. To our knowledge, this is the highest amplitude generated with optically driven Josephson junctions so far and the first successful proof of principle for parallelizing the optical pulse drive to achieve higher output voltages in the future.
The optoelectronic coupling for a pulse-driven Josephson junction array (JJA) for use as a quantum voltage synthesizer has been designed. This system uses optoelectronic components to drive a group of JJAs in parallel. Since the drive system is electrically isolated from the JJAs, they can be connected in series, leading to a higher output voltage. A thin film circuit, including interdigitated capacitors to couple a photodiode to the JJAs has been designed and tested and shown to meet the design goals.