Introduction to Josephson Junction–Based Superconducting Parametric Amplifiers

Abstract

The detection of weak microwave signals with minimal added noise is a central requirement of superconducting quantum technologies. Josephson junction–based parametric amplifiers address this challenge by exploiting the nonlinear inductance of superconducting circuits to transfer energy from a strong pump to a weak signal. Their ability to operate close to the quantum noise limit makes them important components of high-fidelity superconducting-qubit readout systems [1].

This talk introduces the physical principles, circuit implementations and performance characteristics of these amplifiers. Starting from the Josephson effect and the concept of parametric amplification, I will explain the roles of the pump, signal and idler, distinguish three-wave from four-wave mixing, and discuss phase-sensitive and phase-preserving operation in relation to the quantum limits on added noise. Representative implementations based on superconducting quantum interference devices (SQUIDs) and superconducting nonlinear asymmetric inductive elements (SNAILs) will illustrate how circuit architecture and magnetic flux can be used to control the nonlinear response [2].  

The discussion will then address the practical trade-offs between gain, bandwidth, noise and dynamic range, including the effects of nonlinear frequency shifts and gain saturation. Particular attention will be given to the use of Josephson-element arrays and engineered circuit coupling to improve amplifier performance. The talk will conclude by connecting these device characteristics to the requirements of qubit readout, highlighting the importance of low-noise amplification for efficient measurement and reliable discrimination between quantum states [3].  

Finally, I will briefly present some of our recent new developments in the field of Josephson junction- based parametric amplifiers at OQC [4].

References

[1] A. Roy and M. Devoret, Quantum-limited Parametric Amplification with Josephson Circuits in the Regime of Pump Depletion, Phys. Rev. B 98, 045405 (2018).

[2] A. Roy and M. Devoret, Introduction to parametric amplification of quantum signals

with Josephson circuits, C. R. Physique 17, 740 (2016).

[3] N. E. Frattini, V. V. Sivak, A. Lingenfelter, S. Shankar, and M. H. Devoret, Optimizing the Nonlinearity and Dissipation of a SNAIL Parametric Amplifier for Dynamic Range, Phys. Rev. Applied 10, 054020 (2018).

[4] B. Chesca, T. Dixon, N. Acharya, R. D. Potharaju, J. W. Dunstan, C. D. Shelly, and O. W. Kennedy, to be published (2026).

Biographical summary

Boris is a Senior Quantum Engineer at Oxford Quantum Circuits, where he has worked since 2022. His background encompasses the physics and applications of Josephson junction-based superconducting devices—including amplifiers, transistors, sensors and ratchet devices—as well as the fundamental physics of high-temperature superconductors.

He obtained his master’s degree from the Faculty of Physics at the University of Bucharest, Romania, in 1991, focusing on ultrasound sensors for non-destructive evaluation. He completed his PhD at the Bogoliubov Laboratory of Theoretical Physics in Dubna, Russia, in 1995, specialising in the theory of superconducting quantum interference devices.

From 1996 to 1998, Boris held an Alexander von Humboldt Fellowship at Forschungszentrum Jülich, Germany, followed by a postdoctoral appointment at Augsburg University from 1998 to 2000.  

He served as a junior professor at Tübingen University from 2000 to 2006. During this time, he completed his Habilitation and was awarded the title of Privatdozent (PD). His Habilitation thesis focused on the experimental investigation of the superconducting order parameter in high-temperature superconductors, with John Clarke serving as the external examiner.

In 2006, he joined the Physics Department at Loughborough University as a Lecturer/Senior Lecturer, before moving into his current role at Oxford Quantum Circuits.