Parallelization of the optical pulse-drive for AC Josephson voltage standards

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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>4</mml:mn> <mml:mstyle scriptlevel="0"/> <mml:mtext>K</mml:mtext> </mml:mrow> </mml:math> , located near the arrays. The balanced photodiode configurations bias the Josephson junctions with ternary current pulses to generate a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>1</mml:mn> <mml:mstyle scriptlevel="0"/> <mml:mrow> <mml:mi>kHz</mml:mi> </mml:mrow> </mml:mrow> </mml:math> bipolar sinusoidal voltage with a nominal root mean square amplitude of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>85</mml:mn> <mml:mstyle scriptlevel="0"/> <mml:mtext>mV</mml:mtext> </mml:mrow> </mml:math> . We determined a spurious free dynamic range and total harmonic distortion of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>110.6</mml:mn> <mml:mstyle scriptlevel="0"/> <mml:mtext>dBc</mml:mtext> </mml:mrow> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>105.0</mml:mn> <mml:mstyle scriptlevel="0"/> <mml:mtext>dB</mml:mtext> </mml:mrow> </mml:math> from the spectrum of the synthesized signal. Applying an additional dither current to each array individually yielded a quantum locking range of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>0.4</mml:mn> <mml:mstyle scriptlevel="0"/> <mml:mtext>mA</mml:mtext> </mml:mrow> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>0.6</mml:mn> <mml:mstyle scriptlevel="0"/> <mml:mtext>mA</mml:mtext> </mml:mrow> </mml:math> . 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.