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Journal of Physics Conference Series

Pulse driven Josephson voltage standard using modulated optical comb

Chiharu Urano, Nobu‐Hisa Kaneko, Masaaki Maezawa, Taro Itatani, Shogo Kiryu

Published Feb 1, 2008• 7 citations
Publisher

Abstract

We have performed an experiment to drive an overdamped superconductor-insulator-normal-insulator-superconductor (SINIS) Josephson junction array (JJA) with modulated current pulse trains, which are generated by modulated ultra short optical pulses. Averaged voltage outputs of the JJA have been systematically measured for various modulation patterns as a function of the bias voltage of an optical modulator. Quantized voltage steps has been clearly observed in accordance with modulation patterns under certain condition of the bias voltage of the optical modulator.

DOI
10.1088/1742-6596/97/1/012269

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In this paper, quantized voltage steps were observed by driving an overdamped Josephson junction array (JJA) with current pulse trains. The current pulse trains were generated by triggering a metal-semiconductor-metal photodetector installed close to JJA at 4.2 K with a mode-locked fiber laser. The intervals of the constant voltage steps were 10 muV, which agrees with the repetition frequency of the light source (49.7 MHz) and the number of Josephson junctions (100) in the JJA. This is the first step toward establishing an ac voltage standard at the National Institute of Advanced Industrial Science and Technology
We report the experimental results on a Josephson junction array (JJA) driven by current pulse trains generated by triggering a photo detector located in a cryostat with an optical comb. The key components in the experimental system are a mode locked fiber laser, a metal-semiconductor-metal (MSM) photoconductive switch, and an overdamped JJA. Optical pulse trains generated at room temperature are transmitted via an optical fiber to the MSM-photo detector installed at 4.2 K, and then converted into electric current pulse trains to drive the overdamped JJA. Quantized voltage steps have been verified at multiples of 10 muV, which agrees with the repetition rate of the pulse laser and the number of Josephson junctions in the JJA.
We have developed a coding technique to drive an overdamped Josephson junction array (JJA) using modulated optical pulses for voltage standard applications. Our system is composed of a multi-channel pulse pattern generator (PPG), a LiNbO 3 (LN) modulator with an electrical multiplexer (MUX), a photodiode (PD), and an over-damped JJA cooled with 4 K GM cryocooler. The modulated optical pulses are transmitted via an optical fiber to a PD that is installed close to the JJA on a cold stage, and they are then converted into an electrical current pulse train in order to drive the JJA. To avoid a problem in our LN modulator system, i.e., the duty-ratio dependence of the output pulse waveform, pseudo signals that maintain the duty ratio at approximately 50% are inserted in the original bit stream. We demonstraited that this technique is applicable for arbitrary return-to-zero (RZ) binary bit streams.
This paper describes development of a new technique to drive Josephson junction arrays (JJA). We have designed and built an optical pulse generator (up to 12 GHz pulse rate) based on a mode-locked laser to feed an ultra-fast photodiode which again can drive current pulses to a JJA. Our preliminary experiments show that precise direct current (dc) voltages can be realized with a JJA with 5000 junctions. The work ultimately aims at development of an arbitrary pulse pattern generator allowing generation of precise arbitrary voltage waveforms.
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.