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Acknowledgements

Pre-Release History

Starting in 2016, Robert Smith started the Rigetti QVM (née qsim) as a substrate to study syntax and semantics for quantum programming languages. At the time, the predominant syntax for quantum programs was the graphical circuit notation, along with its accompanying LaTeX syntax qasm. It also served as a foundation for understanding "computational quantum computation".

The first Rigetti QVM implemented something akin to the "many worlds" interpretation of quantum mechanics. Quantum programs were written directly as Lisp programs, and each measurement split the "state of the universe", and simulation tracked across each universe. This proved neither efficient nor useful in the study and execution of near-term algorithms, so it was changed to operate in the usual mode with stochastic collapse of the wavefunction.

With Will Zeng's motivation, the QVM moved in a direction of being more accessible. In order to make quantum programs easier to write, a text-based S-expression syntax was used, until the development of CL-QUIL and quilc, which included a parser for a quantum programming language—an assembly-like language called Quil. The QVM ended up being an implementation of Quil's quantum abstract machine.

The Rigetti QVM eventually implemented the full Quil language, and was deployed as the primary backend to the Forest 1.0 service by the end of 2016.

The QVM implemented a relatively efficient form of pure-state evolution, though it didn't go through a handful of microarchitecture optimizations until later. With Nick Rubin constantly challenging the speed of the QVM, the QVM saw improvements over the course of a year, bringing it to a level that was relatively competitive with other simulators. Later, full multithreading was implemented.

Additional modes of execution for noisy simulations were added by Nikolas Tezak and Erik Davis in 2017 and 2018 respectively. In 2017, Robert Smith implemented the JIT compiler for Quil, causing it to outperform OpenMP-optimized C programs, sometimes by a factor between 2 and 10.

During the development of the QVM, many people have made a range of contributions. A summary of these can be found at the end of this document.

The Rigetti QVM has benefited extensively from internal testers at Rigetti. We provide special acknowledgement to Johannes Otterbach, who found countless functional and performance issues. The QVM also benefited from the thousands of users of Quantum Cloud Services.

Credits Roll

For security and privacy, the git history has been removed. The contributors of the project, in approximately the order of their commit count according to git shortlog --summary --numbered, prior to open-sourcing were:

  • Robert Smith (main developer)
  • Erik Davis (density matrix simulation)
  • Zach Beane (porting to CCL & LispWorks)
  • Nikolas Tezak (stochastic simulation)
  • Mark Skilbeck (porting and testing on Windows)
  • Peter Karalekas (release management, automated testing, versioning, nat-tuple testing ☺️)
  • Eric Peterson (fixes and improvements to the app)
  • Will Zeng (installation, Dockerization, deployment, GHZ-on-a-grid in original QIL)
  • Nick Rubin (VQE improvements)
  • Anthony Polloreno (wavefunction sampling)
  • Aaron Vontell (runtime safety checks)
  • Johannes Otterbach (extensive testing and documentation improvements)

Open Source

The Rigetti QVM proudly depends on the work of the open source community, as well as SBCL, ASDF, and Zach Beane's continued maintenance of the Quicklisp project and repository.