# Quantum circuit optimizations for NISQ architectures

## TL;DR

This paper presents a circuit synthesis method that optimizes quantum circuits for specific hardware connectivity constraints, demonstrated on major quantum chips and compared across various circuit sparseness levels.

## Contribution

The authors develop a new circuit synthesis scheme that respects hardware connectivity, independently of prior similar work, and apply it to real quantum chip architectures.

## Key findings

- Effective circuit transformations for Google's Bristlecone, IBM's Tokyo, and Rigetti's Acorn chips.
- Performance varies with circuit sparsity and connectivity constraints.
- Independent of similar recent optimization schemes.

## Abstract

Currently available quantum computing hardware platforms have limited 2-qubit connectivity among their addressable qubits. In order to run a generic quantum algorithm on such a platform, one has to transform the initial logical quantum circuit describing the algorithm into an equivalent one that obeys the connectivity restrictions. In this work we construct a circuit synthesis scheme that takes as input the qubit connectivity graph and a quantum circuit over the gate set generated by $\{\text{CNOT},R_{Z}\}$ and outputs a circuit that respects the connectivity of the device. As a concrete application, we apply our techniques to Google's Bristlecone 72-qubit quantum chip connectivity, IBM's Tokyo 20-qubit quantum chip connectivity, and Rigetti's Acorn 19-qubit quantum chip connectivity. In addition, we also compare the performance of our scheme as a function of sparseness of randomly generated quantum circuits. Note: Recently, the authors of arXiv:1904.00633 independently presented a similar optimization scheme. Our work is independent of arXiv:1904.00633, being a longer version of the seminar presented by Beatrice Nash at the Dagstuhl Seminar 18381: Quantum Programming Languages, pg. 120, September 2018, Dagstuhl, Germany, slide deck available online at https://materials.dagstuhl.de/files/18/18381/18381.BeatriceNash.Slides.pdf.