qstack: Compositional End-to-End Compilation for Fault-Tolerant Quantum Programs

TL;DR

qstack is a novel compiler framework that enables seamless, compositional end-to-end compilation of fault-tolerant quantum programs, integrating quantum and classical components automatically.

Contribution

It introduces a purely quantum intermediate representation with callback wrapping, allowing automatic, compositional compilation of quantum error correction and ISA translation.

Findings

Successfully compiled high-level quantum programs to hardware-native instructions.

Demonstrated integration of multiple error-correcting codes within the compilation pipeline.

Enabled end-to-end compilation from logical gates to fault-tolerant hardware operations.

Abstract

Compiling quantum programs for fault-tolerant execution requires transforming high-level operations through multiple abstraction layers: from logical gates to error-corrected encodings to hardware-native instructions. A key challenge is that quantum error correction turns purely quantum programs into hybrid quantum-classical programs, where classical feedback from syndrome measurements drives quantum corrections at runtime. Existing compilation frameworks handle these quantum and classical components separately, requiring manual adaptation of classical logic at each compilation stage, all while preserving program semantics. We present qstack, a compiler framework built around a purely quantum intermediate representation in which classical logic is accessed only through opaque callbacks, written in any classical language. The framework's central mechanism, callback wrapping, enables compositional compilation: each compiler pass automatically adapts both quantum operations and their associated classical callbacks, and any kernel dynamically generated by a callback is compiled through the full pipeline. This allows ISA translation and quantum error correction to be expressed as composable compiler passes, including concatenation of error-correcting codes, without manual intervention. We demonstrate end-to-end compilation from a high-level gate set through Clifford gates to trapped-ion native operations, with bit-flip and phase-flip repetition codes, the Steane code, and the Shor code obtained by composing two repetition passes.