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arXiv:1602.02650 · Physical Review Applied

Josephson Traveling-Wave Parametric Amplifier with Three-Wave Mixing

Alexander B Zorin

Published Sep 12, 2016• 124 citations
arXivHTMLPDF

Abstract

Josephson parametric amplifiers (JPAs) are important tools in quantum information technology, and traveling-wave JPAs with extended bandwidth are especially desired for frequency multiplexing, $e.g.$ in qubit readout. So far these devices have required the four-wave mixing condition to operate. The author shows, however, that there is a way to realize $t\phantom{\rule{0}{0ex}}h\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}e-w\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}v\phantom{\rule{0}{0ex}}e$ mixing, with negligible phase mismatch. This simple traveling-wave amplifier would offer large gain, wide bandwidth, and ultimately quantum-limited characteristics, outperforming its state-of-the-art four-wave counterparts.

DOI
10.1103/physrevapplied.6.034006

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Josephson parametric amplifiers (JPAs) are important tools in quantum information technology, and traveling-wave JPAs with extended bandwidth are especially desired for frequency multiplexing, e.g.e.g.e.g. in qubit readout. So far these devices have required the four-wave mixing condition to operate. The author shows, however, that there is a way to realize t\phantom{\rule{0}{0ex}}h\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}e-w\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}v\phantom{\rule{0}{0ex}}e mixing, with negligible phase mismatch. This simple traveling-wave amplifier would offer large gain, wide bandwidth, and ultimately quantum-limited characteristics, outperforming its state-of-the-art four-wave counterparts.
Abstract A Josephson traveling-wave parametric amplifier (JTWPA) is indispensable for the high-fidelity readout of superconducting qubits, owing to its broadband gain and near-quantum-limited noise performance. Conventional JTWPAs implemented with 0-Josephson junctions (0-JTWPAs) avoid magnetic-flux bias but rely on Kerr nonlinearity, which leads to pump-power-dependent phase mismatch, gain ripple, and a limited dynamic range. More recently, three-wave-mixing (3WM) JTWPAs employing flux-biased rf-SQUIDs have been proposed to suppress Kerr effects. However, these designs require a significant external flux bias per unit cell, which complicates cryogenic hardware, introduces sensitivity to flux noise, and limits scalability in large arrays. In this study, we propose and analyze a π -junction-based JTWPA ( π -JTWPA) in which the intrinsic π phase shift of the junction effectively displaces the operating point of the current–phase relation. This approach aims to realize 3WM-type nonlinearity with reduced flux bias while preserving broadband amplification, thereby simplifying flux-bias distribution, enhancing robustness against flux noise, and providing a pathway toward scalable, multiplexed quantum readout architectures. In addition, we examine the potential applicability of the π -JTWPA in four-wave-mixing (4WM) operation.
Superconducting traveling-wave parametric amplifiers (TWPAs) are increasingly used in various applications, including quantum computing, quantum sensing, and dark matter detection. However, one important characteristic of these amplifiers, gain compression, has not received much attention. As a result, there is a lack of comprehensive experimental exploration of this phenomenon in the existing literature. In this study, we present an experimental investigation of gain compression in a Josephson traveling-wave parametric amplifier based on a four-wave mixing process. We have implemented a novel setup to monitor the complex transmission of both the pump and signal tones, which allows us to simultaneously track pump depletion and signal amplification as functions of signal power and frequency across the entire bandwidth of the device. Our findings indicate that, while pump depletion occurs during gain compression, it is not the only mechanism involved in the saturation of a TWPA. Power-induced phase-matching processes also take place within the device. This study provides valuable insights for optimizing TWPAs for applications that require high total input power, such as multiplexed qubit readout or broadband photon emission.
Superconducting traveling-wave parametric amplifiers (TWPAs) are increasingly used in various applications, including quantum computing, quantum sensing, and dark matter detection. However, one important characteristic of these amplifiers, gain compression, has not received much attention. As a result, there is a lack of comprehensive experimental exploration of this phenomenon in the existing literature. In this study, we present an experimental investigation of gain compression in a Josephson traveling-wave parametric amplifier based on a four-wave mixing process. We have implemented a novel setup to monitor the complex transmission of both the pump and signal tones, which allows us to simultaneously track pump depletion and signal amplification as functions of signal power and frequency across the entire bandwidth of the device. Our findings indicate that, while pump depletion occurs during gain compression, it is not the only mechanism involved in the saturation of a TWPA. Power-induced phase-matching processes also take place within the device. This study provides valuable insights for optimizing TWPAs for applications that require high total input power, such as multiplexed qubit readout or broadband photon emission.
Quantum-limited parametric amplifiers have become increasingly interesting and relevant with the progressing field of quantum computing. However, currently it is still challenging to fabricate these complex devices. In this thesis, we developed cross type Josephson junctions (JJs), lumped element LC resonators, lumped element Josephson parametric amplifiers (JPAs) and Josephson traveling wave parametric amplifiers (JTWPAs). We found and resolved several fabrication issues however we suspect that both the JPA and JTWPA suffered from microshorts in the circuits during the cryogenic measurements. Nevertheless, we managed to measure the resonance frequency of the JPA and have noticed the flux focusing effect when we flux tune it. We preformed room temperature measurements on over 300 JJs and calculated the relative standard deviation (RSD) for various JJ sizes. We found the spread of 30 fabricated resonators and a rough estimate of their Q factors. The JTWPAs developed are non-degenerate four wave mixing amplifiers that use the resonant phase matching (RPM) technique to reduce the phase mismatch problem. The transmission through the measured JTWPA showed 50 dB loss probably caused by presumably a short from the transmission line to ground. However, when the JTWPA was driven with a pump we observed 20 dB increase in transmission in some frequency bands.
In order to build a large-scale quantum computer, one of the requirements is high-fidelity multiplexed qubit readout, which in turn relies on the use of ultralow-noise amplifiers. While Josephson Parametric Amplifiers (JPAs), using a cavity with few Josephson junctions, have shown promising results for single qubit readout, they have limitations such as low saturation power and a gain-bandwidth product restriction. This makes them less suited for frequency multiplexed qubit readout. A current-pumped Josephson Travelling-Wave Parametric Amplifier (JTWPA), using 4-wave mixing in a lumped-element transmission line, features both high saturation power as well as no restriction on large bandwidth and high gain. This is possible due to multiple junctions and the lack of a cavity. However, also this current pumped JTWPA has an inherent problem, namely phase mismatch between the pump and the signal. This prevents exponential gain. In this thesis, a current pumped JTWPA using the resonant phase matching (RPM) technique to reduce the phase mismatch problem is studied and characterised. The JTWPA shows high gain, high saturation power and a large signal-to-noise ratio improvement. The JTWPA is also used for qubit readout, for which it clearly improves the readout fidelity.
Josephson traveling-wave parametric amplifiers (TWPAs) enable the amplification of weak microwave signals close to the quantum limit with large bandwidth, which has a broad range of applications in superconducting quantum computing and in the operation of single-photon detectors. While the large bandwidth allows for their use in frequency-multiplexed detection architectures, an increased number of readout tones per amplifier puts more stringent requirements on the dynamic range to avoid saturation. Here, we characterize the undesired mixing processes between the different frequency-multiplexed tones applied to a Josephson TWPA, a phenomenon also known as intermodulation distortion. The effect becomes particularly significant when the amplifier is operated close to its saturation power. Furthermore, we demonstrate that intermodulation distortion can lead to significant crosstalk and reduction of fidelity for multiplexed readout of superconducting qubits. We suggest using large detunings between the pump and signal frequencies to mitigate crosstalk. Our work provides insights into the limitations of current Josephson TWPAs and highlights the importance of performing further research on these devices.