QFAST: Conflating Search and Numerical Optimization for Scalable Quantum Circuit Synthesis

TL;DR

QFAST introduces a scalable quantum circuit synthesis method that combines search and numerical optimization, producing shorter circuits faster and capable of handling more qubits than previous techniques.

Contribution

It presents a novel circuit representation enabling efficient optimization, significantly improving scalability and circuit quality over existing methods.

Findings

QFAST produces circuits up to 1.19x longer than optimal but with faster compilation.

It scales up to seven qubits, surpassing previous methods.

QFAST generates circuits 331x shorter than rule-based techniques, with some trade-offs in speed.

Abstract

We present a quantum synthesis algorithm designed to produce short circuits and to scale well in practice. The main contribution is a novel representation of circuits able to encode placement and topology using generic "gates", which allows the QFAST algorithm to replace expensive searches over circuit structures with few steps of numerical optimization. When compared against optimal depth, search based state-of-the-art techniques, QFAST produces comparable results: 1.19x longer circuits up to four qubits, with an increase in compilation speed of 3.6x. In addition, QFAST scales up to seven qubits. When compared with the state-of-the-art "rule" based decomposition techniques in Qiskit, QFAST produces circuits shorter by up to two orders of magnitude (331x), albeit 5.6x slower. We also demonstrate the composability with other techniques and the tunability of our formulation in terms of circuit depth and running time.