quil

Quil is a quantum programming language developed by Rigetti Computing for describing quantum circuits and the classical control logic that governs them. It is designed as an assembly-like language that enables programmers to specify quantum operations, measurements, and the use of classical memory to influence subsequent instructions, allowing the implementation of adaptive and conditional algorithms on near-term quantum devices and simulators.

Quil programs express a mix of quantum gates and classical instructions. The language supports parametric gates, measurement results stored in classical registers, and operations that depend on those results via conditional statements. This combination makes Quil suitable for executing hybrid quantum–classical workflows, such as variational algorithms and error-mitigation routines, where quantum subroutines are coupled with classical optimization loops. Quil is intended to be portable across Rigetti’s hardware and their software stack, and it is commonly used with the PyQuil library, which provides a Python interface for constructing Quil programs and interfacing with the Quantum Virtual Machine (QVM) simulator and Rigetti’s quantum processing units (QPUs).

Ecosystem and tooling around Quil form part of the Forest software stack, including open-source components and documentation. PyQuil helps researchers write Quil code more conveniently, test algorithms on simulators, and then run experiments on actual quantum hardware. Quil’s design emphasizes explicit control over quantum resources and close interaction with classical computation, reflecting the current focus of quantum computing on near-term devices. While OpenQASM and other frameworks address similar goals in the broader ecosystem, Quil remains Rigetti’s primary language for programming their quantum processors.