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Conference on Precision Electromagnetic Measurements

Realization of an Opto-Electronic Bias for Pulse-Driven Josephson Voltage Standards at PTB

Jonas Herick, L. Palafox, Eivind Bardalen, Stephan Bauer, Ralf Behr, Bjørnar Karlsen, Oliver Kieler, Helge Malmbekk

Published Aug 1, 2020• 8 citations
Publisher

Abstract

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.

DOI
10.1109/cpem49742.2020.9191913

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IEEE Transactions on Applied Superconductivity•Mar 16, 2019•30 citations
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.
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.
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.
Quantum-accurate arbitrary voltage waveforms have been generated using electrical pulse driven Josephson junction arrays (JJAs) by several groups [1, 2]. An alternative method is to use optoelectronic components to convert the electrical pulse drive into an optical signal which is subsequently converted by a photodiode into an electrical drive signal connected directly to the JJA. This optoelectronic pulse drive system has several advantages. Due to the electrical isolation between electrical pulse drive and JJA, it is possible to connect several arrays in series without the requirement for complex electrical compensation circuits. This allows larger output voltages to be realized. An optoelectronic drive also offers the ability to easily tune pulse height, via continuous optical attenuation, allowing the drive signal to be tuned to the middle of the JJA constant voltage step giving optimum operation margins. We here present an optoelectronic pulse drive which forms part of a system incorporating a JJA and delta sigma feedback loop [3] for quantum-accurate digitization of arbitrary voltage waveforms. Results showing the generation of quantum-accurate voltages synchronized to the feedback loop master clock are presented.
We developed an optical pulse-drive for the operation of the Josephson Arbitrary Waveform Synthesizer (JAWS) using a fast photodiode (PD) operated at 4 K, close to the JAWS chip. The optical pulses are transmitted to the PD by an easily removable optical fiber attached to it. A bare-lensed PD is mounted by flip-chip technique to a custom-made silicon-carrier chip. This carrier chip is equipped with coplanar waveguides to transmit the electrical pulses from the PD to the JAWS chip mounted on a separate printed circtuit board (PCB). The main components of this optical setup are a laser source, a high-speed Mach-Zehnder modulator, and the modulator driver. The waveform pattern is supplied by a commercial pulse pattern generator providing up to 15 GHz electrical return-to-zero (RTZ)-pulses. Unipolar sinusoidal waveforms were synthesized. Using a JAWS array with 3000 junctions, an effective output voltage of 6.6 mV root mean square (RMS) at the maximum available clock-frequency of 15 GHz was achieved. Higher harmonics were suppressed by more than 90 dBc at laser-bias operation margins of more than 1 mA.