Cirq Turns 1.0

Today we are excited to announce the first full version release of the open source quantum programming framework Cirq: Cirq 1.0. Cirq is a Python framework for writing, running, and analyzing the results of quantum computer programs. It was designed for near-term quantum computers, those with a few hundred qubits and few thousands of quantum gates. The significance of the 1.0 release is that Cirq has support for the vast majority of workflows for these systems and is considered to be a stable API that we will only update with breaking changes at major version numbers.

Getting to Cirq 1.0 is the culmination of a large amount of hard work by hundreds of contributors from Google, industry, and academia. We have been running a weekly meeting, called the “Cirq Cync”, for over four years where community members gather to discuss work on Cirq, bugs, and to generally tell terrible but amusing quantum programming jokes. We’re proud of this inclusive community, and we’ve been particularly happy to see the growth of many software developers into quantum computing experts, and quantum computing experts into solid software developers. One of our contributors, Victory Omole, won the 2021 Witteck Quantum Prize for Open Source Software. Way to go Victory!

The first commit to Cirq on GitHub (an internal version of Cirq at Google existed prior to this) was on Dec 19, 2017 by Craig Gidney, and we publicly announced Cirq in July of 2018. 3,200+ commits later to the GitHub repo, in the hands of the team at Google and the Cirq community, we’ve seen Cirq help accomplish some amazing things:

• Cirq is the lingua franca that Google’s hardware team uses to write quantum programs that run on Google’s quantum computing hardware. Because of this, we have been able to post open source code in our ReCirq repo for these experiments for anyone to examine and extend. A few highlights of the past few years:

• “Realizing topologically ordered states on a quantum processor”, K. J. Satzinger et al., Science 374 6572, 1237-1241 (2021) [paper] [ReCirq code]

• “Information scrambling in quantum circuits”, X. Mi, P. Roushan, C. Quintana et al, Science 374, 6574 1479-1483 (2021) [paper] [ReCirq code]

• “Hartree-Fock on a superconducting qubit quantum computer”, F. Arute et al., Science 369, 6507 1084--1089 (2020) [paper] [ReCirq code]

• A healthy community of libraries have now been built on top of Cirq, enabling different quantum computing research areas. These libraries include:

• TensorFlow Quantum: a tool for exploring quantum machine learning. Using TensorFlow Quantum researchers trained a machine learning model on 30 qubits at a rate of 1.1 petaflops per second (1.1 x 1015 operations per second).

• OpenFermion: an open source tool for quantum computations involved in chemistry simulations.

• Pytket (pytkey-cirq): an open source Python tool for optimizing and manipulating quantum circuits.

• Mitiq: an open source library developed by the non-profit Unitary fund for error mitigation techniques developed by the non-profit Unitary fund.

• Qsim: a high performance state vector simulator written using AVX/FMA vectorized instructions with optional GPU acceleration. qsimcirq is the Cirq interface one can use to access qsim from Cirq.

• Numerous quantum computing cloud services from companies in the industry have also integrated/standardized Cirq. Programs written in Cirq can be used to run through AQT, IonQ, Pascal, Rigetti, and IQM vendors. In addition, Cirq can be used on Azure Quantum to run on the hardware supported by Azure Quantum. Finally, one can get realistic noise simulations of Google’s quantum computing hardware using our newly released Quantum Virtual Machine.

• Cirq is not just for stuffy research. Cirq has also been used to help develop Quantum Chess, a version of chess that uses superposition and entanglement. This notebook shows you how the game of Quantum Chess can be programmed using Cirq.

Cirq moving to its first full version does not just come with new features (see 1.0 release notes), but also with more guarantees about stability. Cirq uses semantic versioning, which means that future point release of Cirq will be compatible with the full version release. For example, version 1.1 of Cirq will not introduce breaking changes to Cirq’s interfaces from version 1.0; only at major version bumps (from 1.x to 2.0, for example) will breaking changes occur.

When we began working on Cirq, quantum computers consisted of only a few qubits and a few quantum gates on these qubits. Building Cirq and the supporting software for these custom systems and having them start to scale to hundreds of qubits over the past (nearly) five years has taught us many lessons. One key takeaway from these lessons is that: As quantum computing hardware continues to grow in scale and complexity, we expect that making software to support this growth will be essential to continue meaningful research and progress. In the next five years, with hardware expected to reach hundreds or even thousands of qubits, the software that is developed for quantum computing will need to have a careful eye set on supporting these bigger and bigger systems. Going forward we will need an ever wider set of frameworks, programming languages, and libraries to achieve quantum computing’s promise.

Acknowledgements

We are indebted to all 169 contributors to the Cirq github repo, and the many more who have filed issues and used Cirq in their own software. A particular shout out to the original lead of Cirq, Craig Gidney, to Cirq’s second lead, ‪Bálint Pató who guided Cirq through its middle ages, and to Alan Ho and Catherine Vollgraff Heidweiller for product wisdom. A special thanks to the core Cirq contributors including Doug Strain, Matthew Neely, Tanuj Khatter, Dax Fohl, Adam Zalcman, Kevin Sung, Matt Harrigan, Casey Duckering, Orion Martin, Smit Sanghavi, Bryan O'Gorman, Wojciech Mruczkiewicz, Ryan LaRose, Tony Bruguier, Victory Omole, and Cheng Xing, and our documentarians Auguste Hirth and Abe Asfaw.

By Dave Bacon and Michael Broughton – Quantum AI Team

Announcing Cirq: an open source framework for NISQ algorithms

Cross-posted from the Google AI Blog

Over the past few years, quantum computing has experienced a growth not only in the construction of quantum hardware, but also in the development of quantum algorithms. With the availability of Noisy Intermediate Scale Quantum (NISQ) computers (devices with ~50 - 100 qubits and high fidelity quantum gates), the development of algorithms to understand the power of these machines is of increasing importance. However, a common problem when designing a quantum algorithm on a NISQ processor is how to take full advantage of these limited quantum devices—using resources to solve the hardest part of the problem rather than on overheads from poor mappings between the algorithm and hardware. Furthermore some quantum processors have complex geometric constraints and other nuances, and ignoring these will either result in faulty quantum computation, or a computation that is modified and sub-optimal.*

Today at the First International Workshop on Quantum Software and Quantum Machine Learning (QSML), the Google AI Quantum team announced the public alpha of Cirq, an open source framework for NISQ computers. Cirq is focused on near-term questions and helping researchers understand whether NISQ quantum computers are capable of solving computational problems of practical importance. Cirq is licensed under Apache 2, and is free to be modified or embedded in any commercial or open source package.

Once installed, Cirq enables researchers to write quantum algorithms for specific quantum processors. Cirq gives users fine tuned control over quantum circuits, specifying gate behavior using native gates, placing these gates appropriately on the device, and scheduling the timing of these gates within the constraints of the quantum hardware. Data structures are optimized for writing and compiling these quantum circuits to allow users to get the most out of NISQ architectures. Cirq supports running these algorithms locally on a simulator, and is designed to easily integrate with future quantum hardware or larger simulators via the cloud.

We are also announcing the release of OpenFermion-Cirq, an example of a Cirq based application enabling near-term algorithms. OpenFermion is a platform for developing quantum algorithms for chemistry problems, and OpenFermion-Cirq is an open source library which compiles quantum simulation algorithms to Cirq. The new library uses the latest advances in building low depth quantum algorithms for quantum chemistry problems to enable users to go from the details of a chemical problem to highly optimized quantum circuits customized to run on particular hardware. For example, this library can be used to easily build quantum variational algorithms for simulating properties of molecules and complex materials.

Quantum computing will require strong cross-industry and academic collaborations if it is going to realize its full potential. In building Cirq, we worked with early testers to gain feedback and insight into algorithm design for NISQ computers. Below are some examples of Cirq work resulting from these early adopters:

• Zapata Computing: simulation of a quantum autoencoder (example code, video tutorial)
• QC Ware: QAOA implementation and integration into QC Ware’s AQUA platform (example code, video tutorial)
• Quantum Benchmark: integration of True-Q software tools for assessing and extending hardware capabilities (video tutorial)
• Heisenberg Quantum Simulations: simulating the Anderson Model
• Cambridge Quantum Computing: integration of proprietary quantum compiler t|ket> (video tutorial)
• NASA: architecture-aware compiler based on temporal-planning for QAOA (slides) and simulator of quantum computers (slides)

To learn more about how Cirq is helping enable NISQ algorithms, please visit the links above where many of the adopters have provided example source code for their implementations.

Today, the Google AI Quantum team is using Cirq to create circuits that run on Google’s Bristlecone processor. In the future, we plan to make this processor available in the cloud, and Cirq will be the interface in which users write programs for this processor. In the meantime, we hope Cirq will improve the productivity of NISQ algorithm developers and researchers everywhere. Please check out the GitHub repositories for Cirq and OpenFermion-Cirq — pull requests welcome!

By Alan Ho, Product Lead and Dave Bacon, Software Lead, Google AI Quantum Team

Acknowledgements
We would like to thank Craig Gidney for leading the development of Cirq, Ryan Babbush and Kevin Sung for building OpenFermion-Cirq and a whole host of code contributors to both frameworks.

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* An analogous situation is how early classical programmers needed to run complex programs in very small memory spaces by paying careful attention to the lowest level details of the hardware.^↩

Announcing OpenFermion: the open source chemistry package for quantum computers

Crossposted on the Google Research Blog

“The underlying physical laws necessary for the mathematical theory of a large part of physics and the whole of chemistry are thus completely known, and the difficulty is only that the exact application of these laws leads to equations much too complicated to be soluble.”
-Paul Dirac, Quantum Mechanics of Many-Electron Systems (1929)

In this passage, physicist Paul Dirac laments that while quantum mechanics accurately models all of chemistry, exactly simulating the associated equations appears intractably complicated. Not until 1982 would Richard Feynman suggest that instead of surrendering to the complexity of quantum mechanics, we might harness it as a computational resource. Hence, the original motivation for quantum computing: by operating a computer according to the laws of quantum mechanics, one could efficiently unravel exact simulations of nature. Such simulations could lead to breakthroughs in areas such as photovoltaics, batteries, new materials, pharmaceuticals and superconductivity. And while we do not yet have a quantum computer large enough to solve classically intractable problems in these areas, rapid progress is being made. Last year, Google published this paper detailing the first quantum computation of a molecule using a superconducting qubit quantum computer. Building on that work, the quantum computing group at IBM scaled the experiment to larger molecules, which made the cover of Nature last month.

Today, we announce the release of OpenFermion, the first open source platform for translating problems in chemistry and materials science into quantum circuits that can be executed on existing platforms. OpenFermion is a library for simulating the systems of interacting electrons (fermions) which give rise to the properties of matter. Prior to OpenFermion, quantum algorithm developers would need to learn a significant amount of chemistry and write a large amount of code hacking apart other codes to put together even the most basic quantum simulations. While the project began at Google, collaborators at ETH Zurich, Lawrence Berkeley National Labs, University of Michigan, Harvard University, Oxford University, Dartmouth College, Rigetti Computing and NASA all contributed to alpha releases. You can learn more details about this release in our paper, OpenFermion: The Electronic Structure Package for Quantum Computers.

One way to think of OpenFermion is as a tool for generating and compiling physics equations which describe chemical and material systems into representations which can be interpreted by a quantum computer¹. The most effective quantum algorithms for these problems build upon and extend the power of classical quantum chemistry packages used and developed by research chemists across government, industry and academia. Accordingly, we are also releasing OpenFermion-Psi4 and OpenFermion-PySCF which are plugins for using OpenFermion in conjunction with the classical electronic structure packages Psi4 and PySCF.

The core OpenFermion library is designed in a quantum programming framework agnostic way to ensure compatibility with various platforms being developed by the community. This allows OpenFermion to support external packages which compile quantum assembly language specifications for diverse hardware platforms. We hope this decision will help establish OpenFermion as a community standard for putting quantum chemistry on quantum computers. To see how OpenFermion is used with diverse quantum programming frameworks, take a look at OpenFermion-ProjectQ and Forest-OpenFermion - plugins which link OpenFermion to the externally developed circuit simulation and compilation platforms known as ProjectQ and Forest.

The following workflow describes how a quantum chemist might use OpenFermion in order to simulate the energy surface of a molecule (for instance, by preparing the sort of quantum computation we described in our past blog post):

1. The researcher initializes an OpenFermion calculation with specification of:

• An input file specifying the coordinates of the nuclei in the molecule.
• The basis set (e.g. cc-pVTZ) that should be used to discretize the molecule.
• The charge and spin multiplicity (if known) of the system.

2. The researcher uses the OpenFermion-Psi4 plugin or the OpenFermion-PySCF plugin to perform scalable classical computations which are used to optimally stage the quantum computation. For instance, one might perform a classical Hartree-Fock calculation to choose a good initial state for the quantum simulation.
3. The researcher then specifies which electrons are most interesting to study on a quantum computer (known as an active space) and asks OpenFermion to map the equations for those electrons to a representation suitable for quantum bits, using one of the available procedures in OpenFermion, e.g. the Bravyi-Kitaev transformation.
4. The researcher selects a quantum algorithm to solve for the properties of interest and uses a quantum compilation framework such as OpenFermion-ProjectQ to output the quantum circuit in assembly language which can be run on a quantum computer. If the researcher has access to a quantum computer, they then execute the experiment.

A few examples of what one might do with OpenFermion are demonstrated in ipython notebooks here, here and here. While quantum simulation is widely recognized as one of the most important applications of quantum computing in the near term, very few quantum computer scientists know quantum chemistry and even fewer chemists know quantum computing. Our hope is that OpenFermion will help to close the gap between these communities and bring the power of quantum computing to chemists and material scientists. If you’re interested, please checkout our GitHub repository - pull requests welcome!

By Ryan Babbush and Jarrod McClean, Quantum Software Engineers, Quantum AI Team

1 If we may be allowed one sentence for the experts: the primary function of OpenFermion is to encode the electronic structure problem in second quantization defined by various basis sets and active spaces and then to transform those operators into spin Hamiltonians using various isomorphisms between qubit and fermion algebras.^↩