Features

Cirq provides useful abstractions for dealing with today’s noisy intermediate-scale quantum (NISQ) computers, where the details of quantum hardware are vital to achieving state-of-the-art results. Some of its features include:

• Flexible gate definitions and custom gates
• Parameterized circuits with symbolic variables
• Circuit transformation, compilation and optimization
• Hardware device modeling
• Noise modeling
• Multiple built-in quantum circuit simulators
• Integration with qsim for

high-performance simulation

• Interoperability with NumPy and

SciPy

• Cross-platform compatibility

Installation

Cirq supports Python version 3.11 and later, and can be used on Linux, MacOS, and Windows, as well as Google Colab. For complete installation instructions, please refer to the Install section of the online Cirq documentation.

Quick Start – “Hello Qubit” Example

Here is a simple example to get you up and running with Cirq after you have installed it. Start a Python interpreter, and then type the following:

import cirq
Pick a qubit.
qubit = cirq.GridQubit(0, 0)
Create a circuit.
circuit = cirq.Circuit(
    cirq.X(qubit)**0.5,  # Square root of NOT.
    cirq.measure(qubit, key='m')  # Measurement.
)
print("Circuit:")
print(circuit)
Simulate the circuit several times.
simulator = cirq.Simulator()
result = simulator.run(circuit, repetitions=20)
print("Results:")
print(result)

Python should then print output similar to this:

Circuit:
(0, 0): ───X^0.5───M('m')───
Results:
m=11000111111011001000

Congratulations! You have run your first quantum simulation in Cirq. You can continue to learn more by exploring the many Cirq tutorials described below.

Cirq Documentation

The primary documentation site for Cirq is the Cirq home page on the Quantum AI website. There and elsewhere, a variety of documentation for Cirq is available.

Tutorials

• [Video tutorials] on YouTube are an engaging way to learn Cirq.
• [Jupyter notebook-based tutorials] let you learn Cirq from your browser – no

installation needed.

• [Text-based tutorials] on the Cirq home page are great when combined with a

local [installation] of Cirq on your computer. After starting with the [basics], you'll be ready to dive into tutorials on circuit building and circuit simulation under the [Build] and [Simulate] tabs, respectively. Check out the other tabs for more!

[Video tutorials]: https://www.youtube.com/playlist?list=PLpO2pyKisOjLVt_tDJ2K6ZTapZtHXPLB4 [Jupyter notebook-based tutorials]: https://colab.research.google.com/github/quantumlib/Cirq [Text-based tutorials]: https://quantumai.google/cirq [installation]: https://quantumai.google/cirq/start/install [basics]: https://quantumai.google/cirq/start/basics [Build]: https://quantumai.google/cirq/build [Simulate]: https://quantumai.google/cirq/simulate

Reference Documentation

• Docs for the [current stable release] correspond to what you get with

pip install cirq.

• Docs for the [pre-release] correspond to what you get with

pip install --upgrade cirq~=1.0.dev.

[current stable release]: https://quantumai.google/reference/python/cirq/all_symbols [pre-release]: https://quantumai.google/reference/python/cirq/all_symbols?version=nightly

Examples

• The examples subdirectory of the Cirq GitHub repo has many

programs illustrating the application of Cirq to everything from common textbook algorithms to more advanced methods.

• The Experiments page on the

Cirq documentation site has yet more examples, from simple to advanced.

Change log

• The Cirq releases page on

GitHub lists the changes in each release.

Integrations

Google Quantum AI has a suite of open-source software that lets you do more with Cirq. From high-performance simulators, to novel tools for expressing and analyzing fault-tolerant quantum algorithms, our software stack lets you develop quantum programs for a variety of applications.

[Qualtran]: https://github.com/quantumlib/qualtran [qsim]: https://github.com/quantumlib/qsim [Stim]: https://github.com/quantumlib/stim [OpenFermion]: https://github.com/quantumlib/openfermion [OpenFermion-FQE]: https://github.com/quantumlib/OpenFermion-FQE [OpenFermion-PySCF]: https://github.com/quantumlib/OpenFermion-PySCF [OpenFermion-Psi4]: https://github.com/quantumlib/OpenFermion-Psi4 [TensorFlow Quantum]: https://github.com/tensorflow/quantum [ReCirq]: https://github.com/quantumlib/ReCirq

Community

Cirq has benefited from [contributions] by over 250 people and counting. We are dedicated to cultivating an open and inclusive community to build software for quantum computers, and have a community [code of conduct].

[contributions]: https://github.com/quantumlib/Cirq/graphs/contributors [code of conduct]: https://github.com/quantumlib/cirq/blob/main/CODEOFCONDUCT.md

Announcements

Stay on top of Cirq developments using the approach that best suits your needs:

• For releases and major announcements: sign up to the low-volume mailing list

[cirq-announce].

• For releases only:

* Via GitHub notifications: configure [repository notifications] for Cirq. * Via Atom/RSS from GitHub: subscribe to the GitHub [Cirq releases Atom feed]. * Via RSS from PyPI: subscribe to the [PyPI releases RSS feed] for Cirq.

Cirq releases take place approximately every quarter.

[cirq-announce]: https://groups.google.com/g/cirq-announce [repository notifications]: https://docs.github.com/github/managing-subscriptions-and-notifications-on-github/configuring-notifications [Cirq releases Atom feed]: https://github.com/quantumlib/Cirq/releases.atom [PyPI releases RSS feed]: https://pypi.org/rss/project/cirq/releases.xml

Questions and Discussions

• Have questions about Cirq? Post them to the [Quantum Computing

Stack Exchange] and tag them with [cirq]. You can also search past questions using that tag – it's a great way to learn!

• Want meet other Cirq developers and participate in discussions? Join

Cirq Cynq, our biweekly virtual meeting of contributors. Sign up to [cirq-dev] to get an automatic meeting invitation!

[Quantum Computing Stack Exchange]: https://quantumcomputing.stackexchange.com [cirq]: https://quantumcomputing.stackexchange.com/questions/tagged/cirq [cirq-dev]: https://groups.google.com/g/cirq-dev

Contributions

• Have a feature request or bug report? [Open an issue on GitHub]!
• Want to develop Cirq code? Look at the [list of good first issues] to

tackle, read our [contribution guidelines], and then start opening [pull requests]!

[Open an issue on GitHub]: https://github.com/quantumlib/Cirq/issues/new/choose [list of good first issues]: https://github.com/quantumlib/Cirq/contribute [contribution guidelines]: https://github.com/quantumlib/cirq/blob/main/CONTRIBUTING.md [pull requests]: https://help.github.com/articles/about-pull-requests

Citing Cirq

When publishing articles or otherwise writing about Cirq, please cite the Cirq version you use – it will help others reproduce your results. We use Zenodo to preserve releases. The following links let you download the bibliographic record for the latest stable release of Cirq in some popular formats:

For formatted citations and records in other formats, as well as records for all releases of Cirq past and present, please visit the Cirq page on Zenodo.

Contact

For any questions or concerns not addressed here, please email quantum-oss-maintainers@google.com.

Disclaimer

This is not an officially supported Google product. This project is not eligible for the Google Open Source Software Vulnerability Rewards Program.

Copyright 2019 The Cirq Developers.