QFAST: Quantum Synthesis Using a Hierarchical Continuous Circuit Space

TL;DR

QFAST is a hierarchical quantum synthesis tool that efficiently generates shorter quantum circuits by combining fast coarse optimization with detailed final refinement, improving scalability and portability across architectures.

Contribution

It introduces a novel hierarchical representation and iterative refinement approach for quantum circuit synthesis, enabling scalable and portable circuit generation.

Findings

QFAST produces significantly shorter circuits than existing methods.

The hierarchical approach improves scalability in quantum circuit synthesis.

The method allows customization of circuit depth and synthesis time.

Abstract

We present QFAST, a quantum synthesis tool designed to produce short circuits and to scale well in practice. Our contributions are: 1) a novel representation of circuits able to encode placement and topology; 2) a hierarchical approach with an iterative refinement formulation that combines "coarse-grained" fast optimization during circuit structure search with a good, but slower, optimization stage only in the final circuit instantiation stage. When compared against state-of-the-art techniques, although not optimal, QFAST can generate much shorter circuits for "time dependent evolution" algorithms used by domain scientists. We also show the composability and tunability of our formulation in terms of circuit depth and running time. For example, we show how to generate shorter circuits by plugging in the best available third party synthesis algorithm at a given hierarchy level. Composability enables portability across chip architectures, which is missing from the available approaches.