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IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems

A Predictive Readout Fidelity Model Considering Nonidealities for Readout Circuit Design in Superconducting Quantum Computers

Yao Tong, Quan Chen

Published Oct 18, 2024• 1 citation
Publisher

Abstract

Superconducting quantum computing hardware relies on classical radio-frequency (RF) electronic circuits to control and measure quantum states. As the complexity of quantum computers increases, the significance of the classical circuitry component grows, necessitating the development of accurate models for its design and optimization. This study presents an analytical model that quantifies the influence of circuit nonidealities on readout fidelity in superconducting quantum computing systems. This model considers a wide range of nonidealities typically encountered in the readout chain, encompassing frequency, amplitude, phase inaccuracies, impedance mismatch, quantum noise, and amplifier noise. It further predicts the combined impact of these nonidealities on fidelity. The model’s precision and efficacy are confirmed through numerical quantum-classical co-simulation. The highest observed relative mismatch is roughly 3.5%, but most errors remain below 1%. Such a model can significantly aid in designing and optimizing practical quantum computers.

DOI
10.1109/tcad.2024.3483670

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Superconducting quantum computing hardware relies on classical radio-frequency (RF) electronic circuits to control and measure quantum states. As the complexity of quantum computers increases, the significance of the classical circuitry component grows, necessitating the development of accurate models for its design and optimization. This study presents an analytical model that quantifies the influence of circuit nonidealities on readout fidelity in superconducting quantum computing systems. This model considers a wide range of nonidealities typically encountered in the readout chain, encompassing frequency, amplitude, phase inaccuracies, impedance mismatch, quantum noise, and amplifier noise. It further predicts the combined impact of these nonidealities on fidelity. The model’s precision and efficacy are confirmed through numerical quantum-classical co-simulation. The highest observed relative mismatch is roughly 3.5%, but most errors remain below 1%. Such a model can significantly aid in designing and optimizing practical quantum computers.
Quantum computers based on spin qubits and superconducting qubits require radio-frequency (RF) electronic circuits to control and read out the state. As the scale of the quantum processors increases, the inaccuracy in the RF circuit becomes an increasingly significant source of nonidealities that impacts the qubit operations. In this article, we propose a closed-form model to characterize the effects of inaccuracies in the controlling RF circuits on the fidelity of single-qubit control operation of superconducting qubits. Different from previous works, our model allows characterization of multiple inaccuracies at the same time, significantly enhancing the guidance capabilities for practical quantum computing hardware design and optimization. In addition, the accuracy of the proposed model is also verified by a quantum-classical co-simulator.
Qubit readout is a critical part of any quantum computer including the superconducting-qubit-based one. The readout fidelity is affected by the readout pulse width, readout pulse energy, resonator design, qubit design, qubit-resonator coupling, and the noise generated along the readout path. It is thus important to model and predict the fidelity based on various design parameters along the readout path. In this work, a simulation methodology for superconducting qubit readout fidelity is proposed and implemented using Matlab and Ansys HFSS to allow co-optimization in the readout path. As an example, parameters are taken from an actual superconducting-qubit-based quantum computer. Without any calibrations, the model is able to predict the readout error of the system as a function of the readout pulse power. It is found that the system can still maintain high fidelity even if the input power is reduced by 7 dB. This can be used to guide the design and optimization of a superconducting qubit readout system.
Quantum computers based on superconducting qubits have emerged as a leading candidate for a scalable quantum processor architecture. The core of a quantum processor consists of quantum devices that are manipulated using classical electronic circuits, which need to be co-designed for optimal performance and operation. As the principles governing the behavior of the classical circuits and the quantum devices are different, this presents a unique challenge in terms of the simulation, design and optimization of the joint system. A methodology is presented to transform the behavior of small-scale quantum processors to equivalent circuit models that are usable with classical circuits in a generic electrical simulator, enabling the detailed analysis of the impact of many important non-idealities. The methodology has specifically been employed to derive a circuit model of a superconducting qubit interacting with the quantized electromagnetic field of a superconducting resonator. Based on this technique, a comprehensive analysis of the qubit operation is performed, including the coherent control and readout of the qubit using electrical signals. Furthermore, the effect of several non-idealities in the system such as qubit relaxation, decoherence and leakage out of the computational subspace are captured, in contrast to previous works. As the presented method enables the co-simulation of the control electronics with the quantum system, it facilitates the design and optimization of near-term superconducting quantum processors.
Superconducting qubits require rapid and high-fidelity multiplexed readout to enable effective quantum computers. However, predicting the fidelity of the physical implementation of a readout chain is challenging, limiting the success of experimental devices. While analytical tools are currently used to support these design efforts, mapping their outputs into a physical design is difficult and prone to error. In this work, we use multiphysics numerical methods to model the effect of individual component values on fidelity, which can more easily guide the design of a physical device geometry. This procedure is utilized here to optimize a pair of key capacitance values, but it is applicable to broader parameterization of a readout chain.
Superconducting qubits require rapid and high-fidelity multiplexed readout to enable effective quantum computers. However, predicting the fidelity of the physical implementation of a readout chain is challenging, limiting the success of experimental devices. While analytical tools are currently used to support these design efforts, mapping their outputs into a physical design is difficult and prone to error. In this work, we use multiphysics numerical methods to model the effect of individual component values on fidelity, which can more easily guide the design of a physical device geometry. This procedure is utilized here to optimize a pair of key capacitance values, but it is applicable to broader parameterization of a readout chain.