# Scqubits: a Python package for superconducting qubits

Peter Groszkowski1 and Jens Koch2

1Pritzker School for Molecular Engineering, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, USA
2Department of Physics and Astronomy, Northwestern University, Evanston, IL 60208, USA

### Abstract

$\textbf{scqubits}$ is an open-source Python package for simulating and analyzing superconducting circuits. It provides convenient routines to obtain energy spectra of common superconducting qubits, such as the transmon, fluxonium, flux, cos(2$\phi$) and the 0-$\pi$ qubit. $\textbf{scqubits}$ also features a number of options for visualizing the computed spectral data, including plots of energy levels as a function of external parameters, display of matrix elements of various operators as well as means to easily plot qubit wavefunctions. Many of these tools are not limited to single qubits, but extend to composite Hilbert spaces consisting of coupled superconducting qubits and harmonic (or weakly anharmonic) modes. The library provides an extensive suite of methods for estimating qubit coherence times due to a variety of commonly considered noise channels. While all functionality of $\textbf{scqubits}$ can be accessed programatically, the package also implements GUI-like widgets that, with a few clicks can help users both create relevant Python objects, as well as explore their properties through various plots. When applicable, the library harnesses the computing power of multiple cores via multiprocessing. $\textbf{scqubits}$ further exposes a direct interface to the Quantum Toolbox in Python (QuTiP) package, allowing the user to efficiently leverage QuTiP's proven capabilities for simulating time evolution.

In this article, we introduce an open-source Python package called $\textbf{scqubits}$, which can be used for modeling and analyzing superconducting circuits. The library provides convenient routines to obtain and explore the energy spectra of many common superconducting qubits, display matrix elements of various operators as well as easily plot qubit wavefunctions. Many of these tools are not limited to single qubits, but extend to composite Hilbert spaces consisting of coupled superconducting qubits and harmonic (or weakly anharmonic) modes. The library also includes an extensive suite of methods for estimating qubit coherence times due to a variety of commonly considered noise channels. Through a set of carefully chosen examples, this article outlines many of the key features of $\textbf{scqubits}$, as well as shows how the package can be use used by both advanced users who perform active research, as well as by students, who may be new to the field.

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[1] The up-to-date API documentation can be found online. URL https:/​/​scqubits.readthedocs.io/​en/​latest/​api-doc/​apidoc.html.

[2] The full documentation for scqubits is located at the following address. URL https:/​/​scqubits.readthedocs.io/​en/​latest.

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### Cited by

[1] Thi Ha Kyaw, Tim Menke, Sukin Sim, Abhinav Anand, Nicolas P. D. Sawaya, William D. Oliver, Gian Giacomo Guerreschi, and Alán Aspuru-Guzik, "Quantum Computer-Aided Design: Digital Quantum Simulation of Quantum Processors", Physical Review Applied 16 4, 044042 (2021).

[2] Andrew Guthrie, Christoforus Dimas Satrya, Yu-Cheng Chang, Paul Menczel, Franco Nori, and Jukka P. Pekola, "A Cooper-Pair Box Architecture for Cyclic Quantum Heat Engines", arXiv:2109.03023.

[3] J. Wills, G. Campanaro, S. Cao, S. D. Fasciati, P. J. Leek, and B. Vlastakis, "Characterisation of spatial charge sensitivity in a multi-mode superconducting qubit", arXiv:2108.02105.

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