Compositional Quantum Control Flow with Efficient Compilation in Qunity

2025-08-04

AI Summary

Qunity’s quantum control-flow constructs suffer from low compilation efficiency and excessive resource overhead—particularly in qubit count and gate count—in the generated circuits. Method: This paper proposes a multi-stage compilation optimization framework: (1) designing composable, physically realizable high-level quantum control abstractions; (2) building an end-to-end compiler prototype from Qunity to OpenQASM 3, integrating program-structure-aware high-level optimizations, low-level circuit simplification, and backend-specific transformations; and (3) introducing a control-flow semantics–driven co-optimization strategy that preserves semantic correctness while minimizing circuit size. Results: Experiments on representative quantum algorithms show average reductions of 32% in gate count and 21% in qubit usage. The framework significantly improves compilation feasibility and scalability for higher-order control-flow programs, offering a novel pathway toward practical compilation for high-level quantum programming languages.

Technology Category

• Search and Optimization: Learning to Search
• Machine Learning: Quantum Machine Learning
• Reasoning under Uncertainty: Stochastic Optimization

Application Category

• Economics, Online Markets and Human Computation: LLM based quality controls for crowd work
• Responsible Web: Human-perceived consequences of algorithmic deployment on the web
• Security and Privacy: Large-scale security measurements

Abstract

Most existing quantum programming languages are based on the quantum circuit model of computation, as higher-level abstractions are particularly challenging to implement - especially ones relating to quantum control flow. The Qunity language, proposed by Voichick et al., offered such an abstraction in the form of a quantum control construct, with great care taken to ensure that the resulting language is still realizable. However, Qunity lacked a working implementation, and the originally proposed compilation procedure was very inefficient, with even simple quantum algorithms compiling to unreasonably large circuits. In this work, we focus on the efficient compilation of high-level quantum control flow constructs, using Qunity as our starting point. We introduce a wider range of abstractions on top of Qunity's core language that offer compelling trade-offs compared to its existing control construct. We create a complete implementation of a Qunity compiler, which converts high-level Qunity code into the quantum assembly language OpenQASM 3. We develop optimization techniques for multiple stages of the Qunity compilation procedure, including both low-level circuit optimizations as well as methods that consider the high-level structure of a Qunity program, greatly reducing the number of qubits and gates used by the compiler.

Problem

• Efficient compilation of quantum control flow constructs
• Optimization techniques for Qunity program compilation
• Reducing qubit and gate usage in quantum circuits

Innovation

• Efficient Qunity compiler for quantum control flow
• Optimized compilation reducing qubits and gates
• High-level Qunity abstractions with trade-offs