OpenQASM 3: A broader and deeper quantum assembly language

TL;DR

OpenQASM 3 extends quantum assembly language to include real-time control flow, external classical functions, and multi-level circuit descriptions, enabling more flexible and precise quantum programming beyond traditional gate-based models.

Contribution

The paper introduces OpenQASM 3, a broader quantum assembly language supporting real-time control, external classical calls, and multi-level circuit descriptions, addressing limitations of previous versions.

Findings

Supports arbitrary control flow and external classical functions.

Enables multi-level circuit and control sequence descriptions.

Facilitates circuit optimization and error mitigation.

Abstract

Quantum assembly languages are machine-independent languages that traditionally describe quantum computation in the circuit model. Open quantum assembly language (OpenQASM 2) was proposed as an imperative programming language for quantum circuits based on earlier QASM dialects. In principle, any quantum computation could be described using OpenQASM 2, but there is a need to describe a broader set of circuits beyond the language of qubits and gates. By examining interactive use cases, we recognize two different timescales of quantum-classical interactions: real-time classical computations that must be performed within the coherence times of the qubits, and near-time computations with less stringent timing. Since the near-time domain is adequately described by existing programming frameworks, we choose in OpenQASM 3 to focus on the real-time domain, which must be more tightly coupled to the execution of quantum operations. We add support for arbitrary control flow as well as calling external classical functions. In addition, we recognize the need to describe circuits at multiple levels of specificity, and therefore we extend the language to include timing, pulse control, and gate modifiers. These new language features create a multi-level intermediate representation for circuit development and optimization, as well as control sequence implementation for calibration, characterization, and error mitigation.