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Journal of Physics Conference Series

A new coding technique in serial data transmission and demodulation with Josephson junctions array

Chiharu Urano, Michitaka Maruyama, Nobu‐Hisa Kaneko, Hirotake Yamamori, Alexandre Shoji, Masaaki Maezawa, Y. Hashimoto, Hideo Suzuki, Shuichi Nagasawa, T. Satoh, Mutsuo Hidaka, Shogo Kiryu

Published Jun 1, 2010• 6 citations
Publisher

Abstract

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.

DOI
10.1088/1742-6596/234/4/042037

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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.
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.
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.
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 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.
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.