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Wuli yu gongcheng.

THE BASIC PRINCIPLE OF SUPERCONDUCTING QUANTUM COMPUTING JOSEPHSON PARAMETRIC AMPLIFIER

Feifan Su, Zhaohua YANG

Published Aug 1, 2024• 0 citations
Publisher

Abstract

The Josephson parametric amplifier is the key to superconducting quantum computing experiments. This article introduces its basic physical principles and provides a detailed discussion on the device physical characteristics, implementation design, and development of Josephson parametric amplifiers. Finally, based on practical experimental experience, an effective method for determining the optimal operating point of Josephson parametric amplifiers was proposed. This article helps readers interested in superconducting quantum computing to comprehensively grasp the experimental methods and system composition of superconducting quantum computing, and has certain reference significance for the design of extremely low temperature signal amplifiers.

DOI
10.26599/phys.2024.9320418

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Conference digest•Jun 24, 2024•0 citations
The Josephson parametric amplifier is the key to superconducting quantum computing experiments. This article introduces its basic physical principles and provides a detailed discussion on the device physical characteristics, implementation design, and development of Josephson parametric amplifiers. Finally, based on practical experimental experience, an effective method for determining the optimal operating point of Josephson parametric amplifiers was proposed. This article helps readers interested in superconducting quantum computing to comprehensively grasp the experimental methods and system composition of superconducting quantum computing, and has certain reference significance for the design of extremely low temperature signal amplifiers.
For the existing superconducting qubit devices, constructing the corresponding high-fidelity gate operation after system calibration is a key step to realize quantum computing. As the fifth chapter of the series of “Introduction to physics frontier—superconducting quantum computing”, this paper systematically discusses the physical picture and basic method of constructing superconducting qubit gate operation through microwave pulse, gives a set of construction process of single bit gate operation, and extends the measurement and optimization development of gate operation fidelity. This paper aims to help the physics teachers, senior undergraduates, graduate students, and science and engineering backgrounds interested in superconducting quantum computing readers to systematically understand the whole basic process of superconducting qubit gate construction and gate operation fidelity measurement and optimization.
Quantum computing has received extensive attention worldwide. In recent years, quantum scientists represented by academician Pan Jianwei have made remarkable progress in quantum computing. In the framework of university physics courses, the timely introduction of superconducting quantum computing theory can not only serve as an organic supplement and update to the quantum mechanics section of university physics courses, but also enable undergraduate students to have earlier exposure to the principles of superconducting quantum computing and its potential applications. This article attempts to reflect the basic principles of superconducting quantum computing, such as Josephson effect, macroscopic quantum properties, superconducting quantum bit manipulation, etc., within the framework of university physics courses. In addition, it also attempts to incorporate Josephson junction room temperature resistance measurement into university physics experiments in university physics courses. These attempts not only help guide them to focus on the forefront of national strategic needs, lay the foundation for their future research and work in related fields, but also have certain reference significance for the ideological and political construction of university physics courses.
Superconducting parametric amplifiers (SPAs) are critical components for ultralow-noise qubit readout in quantum computing, addressing the critical challenge of amplifying weak quantum signals without introducing noise that degrades coherence and computational fidelity. Unlike classical amplifiers, SPAs can achieve or closely approach quantum-limited performance, specifically the Standard Quantum Limit (SQL) of half a photon of added noise for phase-preserving amplification. The core principle of SPAs relies on parametric amplification, where energy is transferred from a strong pump tone to a weak input signal through non-dissipative nonlinear mixing processes. This is enabled by intrinsic nonlinearities in superconducting materials, primarily kinetic inductance in thin films (e.g., NbTiN, Al) and, more significantly, the Josephson effect in Josephson junctions. These nonlinear elements facilitate frequency mixing (three-wave or four-wave mixing) and can operate in phase-preserving or phase-sensitive amplification modes, with the latter allowing for noise squeezing below the SQL. This chapter emphasizes the significant role of resonator design in determining critical SPA performance metrics such as gain, bandwidth, and noise characteristics. It details both lumped-element (LC) and distributed-element (coplanar waveguide, CPW) resonators, discussing their unique properties, suitability for different frequency ranges, and the importance of achieving high-quality factors (Q) for efficient energy storage and minimal loss. A practical design and simulation of a meandered quarterwavelength CPW resonator coupled to a feed line is presented, illustrating how precise control over geometric parameters optimizes resonant frequency, coupling strength, and quality factor for high-fidelity qubit state discrimination.
Nowadays, it is possible to control and measure the quantum state of systems with a few degrees of freedom, whether they are microscopic objects like cold atoms and single photons, or macroscopic objects like superconducting circuits. Such delicate experiments require an interface which bridges the gap of orders of magnitudes in energy between the quantum object and the data acquisition system. This problem is solved by an active device: the amplifier. Although the amplifier is necessary to overcome the noise at the stage of data acquisition, it eventually alters the signal. We have developed an amplifier for microwave signals which adds only the minimum of noise allowed by quantum laws: the equivalent of half a photon of noise referred to the input. Our amplifier is based on a superconducting circuit of Josephson junctions in superconducting resonators. We found a way to make it practical to use by tuning its center frequency over 500 MHz. We are now trying to increase its bandwidth for a given gain using more compact resonators. In this talk, I will show how the amplifier works and also its applications to quantum information processing. This circuit can be used to generate and combine twin microwave photons within an integrated circuit. Finally, I will show that such an amplifier allows real time measurement of the state of a qubit and quantum feedback protocols.
Near-quantum-limited amplifiers are essential building blocks for high-fidelity readout of superconducting qubits. Josephson parametric amplifiers (JPAs) have been developed to achieve this ultra-low-noise performance [1] in the last two decades by exploiting the quartic term in the nonlinear energy-phase relation of Al-AlO X superconductor-insulator-superconductor Josephson Junctions (SIS JJs). An ongoing research focus is to enhance JPAs’ compression power for processing readout signals in large-scale quantum processors. One approach is to optimize circuit designs to minimize parasitic higher-order nonlinear terms while preserving the quartic nonlinearity for the amplification process. An alternative approach is to make use of new types of JJ devices with small quartic nonlinearity such that parasitic nonlinearities are inherently even lower. Here, we demonstrate that superconductor-semiconductor-superconductor (SSmS) JJs, realized with Al-InAs heterostructures are a promising device to realize quantum-limited amplifiers for superconducting quantum computing. Al-InAs JJs have been used to realize qubits [2] , voltage-tunable resonators [3] , and parametric amplifiers [4] by exploiting critical current tunability via gate voltage ( Fig. 1(a–b) ). In this work, for the first time, we experimentally studied the nonlinear energy-phase relation of Al-InAs JJs and revealed their inherently low quartic nonlinearity. Next, we demonstrate a four-wave-mixing (4WM) parametric amplifier made with an Al-InAs junction that achieves greater than 20 dB of gain, 6 MHz of bandwidth and −119 dBm of compression power.