Decomposition of Multi-Qubit Gates for Circuit Cutting

TL;DR

This paper introduces a new method for decomposing multi-qubit gates in quantum circuits to reduce sampling overhead during circuit cutting, improving efficiency in large-scale quantum computations.

Contribution

It proposes a modified decomposition strategy for multi-qubit gates that decreases sampling overhead by using additional ancilla qubits at cut locations.

Findings

The method effectively reduces sampling overhead for MCX and CCCX gates.

Introducing a small number of ancilla qubits improves decomposition efficiency.

The approach enhances the practicality of circuit cutting in large quantum circuits.

Abstract

A large-scale quantum circuit can be partitioned into multiple subcircuits through circuit cutting, where each subcircuit is executed multiple times and the expectation value of the original circuit is reconstructed by classical post-processing from their measurement (sampling) results. In this process, appropriate cut locations are identified after the user-designed quantum circuit, including multi-qubit gates that act on three or more qubits, has been decomposed into single-qubit gates and two-qubit gates such as the CNOT gate. Here, we present a method for reducing the sampling overhead, which refers to the increase in the number of samples required due to the cutting process, by modifying the decomposition strategy of multi-qubit gates. Using MCX and CCCX gates as representatives of multi-qubit gates, we demonstrate that the proposed decomposition method, which introduces a small number of ancilla qubits according to the identified cut locations, effectively decreases the sampling overhead.