Using S Gates and Relative Phase Toffoli Gates to Improve T-Count in Quantum Boolean Circuits

Abstract

Toffoli gates are an important primitive in reversible Boolean logic. In quantum computation, these Toffoli gates are composed using other elementary gates, most notably the Clifford+T basis. However, in fault-tolerant implementations of quantum circuits, a non-transversal gate like the T gate incurs extra cost relative to transversal gates like the S and CNOT gates. Relative-phase Toffoli Gates (RTOF) have been proposed as a way to minimize this "T-depth" at the cost of incurring a relative phase that could skew the final quantum states. While previous research has proposed a way to use transversal S gates to eliminate this relative phase, this paper proposes a novel form of the RTOF that incorporates S gates in order to simplify generation of the logic to return the phase