Driving a low critical current Josephson junction array with a mode-locked laser

Abstract

We report proof-of-concept experiments on an optically driven Josephson voltage standard based on a mode-locked laser (MLL), a time-division multiplexer, and a cryogenic ultrafast photodiode driving an overdamped Josephson junction array (JJA). Our optical pulse pattern generator (PPG) concept builds on the capability of MLLs to produce trains of picosecond-wide optical pulses with little amplitude and temporal spread. Our present setup enables multiplication of the original 2.3 GHz pulse repetition frequency by a factor of 8. A commercial photodiode converts the optical pulses into about 25 ps wide electrical pulses in liquid helium several cm from the JJA. Using a custom-made MLL, we can drive a JJA with a low critical current of 360 μA at multiple Shapiro steps. We have performed experiments with pulse pairs whose time interval can be set freely without distorting the shapes of individual pulses. Experimental results are in qualitative agreement with theoretical simulations, and they demonstrate, e.g., crossover in the Shapiro step pattern when the time interval between the pulses is approximately equal to the inverse of the characteristic frequency of the JJA. However, there are quantitative discrepancies, which motivate an improved integration of photodiodes and JJAs to improve both the understanding and fidelity of Josephson Arbitrary Waveform Synthesizers. Considering future quantum technologies in a wider perspective, our optical approach is a potential enabler for fast and energy-efficient pulse drive without an expensive high-bandwidth electrical PPG and without high-bandwidth electrical cables that yield too high thermal conductance between cryogenic and room temperatures.

The Photodetection of Ultrashort Optical Pulse Trains for Low Noise Microwave Signal Generation

“…Photodetector operation at cold temperatures could aid in understanding noise properties as well, with the added benefit of supporting experimental endeavors linking photonic systems with superconducting circuits. [36,37,112] At room temperature, photocarrier transport noise is believed to be dominated by scattering off lattice phonons. At cryogenic temperatures, presumably such scattering is suppressed, and lower noise may result.…”

“…[30,31] High-fidelity optical pulse detection is also used as a diagnostic tool to measure optical pulse-to-pulse timing jitter, [32][33][34] the characterization of which is needed for a broad class of optical pump-probe experiments. Further applications include optical two-way time transfer, [35] and photonic links to cryogenic temperatures for applications in superconducting circuits, [36] perhaps even aiding quantum information systems with superconducting qubits. [37] A few selected applications of low noise optical pulse detection are shown in Figure 1.…”

Josephson voltage standards as toolkit for precision metrological applications at PTB

“…Many further papers on implementation techniques, measurement setups, investigations and waveform synthesis (Ireland et al 2017, 2019, Bardalen et al 2020, Karlsen et al 2020, Nissilä et al 2021, Brevik et al 2022 indicate that the optical drive is a very active field with high potential for applications.…”

Quantum standards for electrical and electro-chemical measurements

“…Recently, the greatest interest has been aroused by the possibility of using optical and opto-electric methods for the displacement of the Josephson junction [12,13]. The use of optical cables makes it possible to organize thermal decoupling and significantly reduce the flow of heat into the cryogenic part of the setup, organize optical decoupling of control signals, and bring the source of the displacement signal closer to the Josephson converter.…”

“…Also, the authors have proposed and investigated methods based on PWM modulation of microwave bias power [11]. The newest way of constructing such devices is based on optical and opto-electric methods of biasing the Josephson junction by pulsed lasers and lasers with different wavelengths [12,13].…”