Improving the number of T gates and their spread in integer multipliers on quantum computing

Abstract

Quantum circuits performing arithmetic operations are critical in quantum computing because of the need for such operations in proven quantum algorithms. Although quantum computers are becoming increasingly resourceful, the number of qubits currently available is still limited. Furthermore, these qubits are heavily affected by internal and external noise. It has been proven that quantum circuits built using Clifford $+T$ gates can be made fault tolerant. However, the use of the $T$ gates comes at a very high cost. If the number of $T$ gates used in a circuit is not optimized, the cost of the circuit will be increased excessively. As a consequence, it is essential to optimize the circuits so that they are as resource efficient as possible and also noise tolerant. This paper presents the design of a circuit to perform the multiplication of two integers. The circuit is built using only Clifford $+T$ gates for compatibility with error detection and correction codes. It outperforms the circuits in the state of the art in terms of $T$ count and $T$ depth.