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arXiv:2507.17164

A Cost-Effective Quantum Boolean-Phase SWAP Gate with Only Two CNOT Gates

Ali Al-Bayaty, Shanyan Chen, Steven A. Bleiler, Marek A. Perkowski

Published Jul 23, 2025• 1 citation
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Abstract

A new Boolean-Phase swapping gate is presented with improved quantum generality and cost-effectiveness. Our swapping gate is termed the "p-SWAP gate", where p is the phase difference selected for a set of swapped qubits. The phase p is expressed in radians and $-π~{\leq}$ p ${\leq}~+π$. The generality of p-SWAP gate is demonstrated for Phase applications for selected values of p and for Boolean applications when the value of p is ignored. The cost-effectiveness of p-SWAP gate follows from the lower quantum cost and depth of its final realized (transpiled) quantum circuit, when compared to the standard SWAP gate composed of three Feynman (CNOT) gates. Specifically, our presented p-SWAP gate utilizes only two CNOT gates. The quantum circuit of the p-SWAP gate is visually designed using our previously developed Bloch sphere approach. Experimentally, after transpilation for an IBM quantum computer, the transpiled p-SWAP gate shows an approximate 23% quantum cost reduction and an approximate 26% depth minimization compared to the transpiled standard SWAP gate.

DOI
10.48550/arxiv.2507.17164

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A Boolean-Phase swapping gate is introduced for quantum generality and cost-effectiveness, which is termed the "p-SWAP gate", where p is a customizable phase difference for a set of swapped qubits and 0 <= p <= ±π{\pm π}±π radians. The generality of the p-SWAP gate is proposed for quantum Phase oracles requiring a desirable p for a set of swapped qubits, as well as for quantum Boolean oracles when p is ignored. The cost-effectiveness of the p-SWAP gate comes from the lower quantum cost and depth for its final synthesized (transpiled) quantum circuit into a quantum computer, as compared to the standard SWAP gate. In general, the standard SWAP gate is constructed using three Feynman (CNOT) gates, while our p-SWAP gate only utilizes two CNOT gates. In this paper, the desirability of p is geometrically chosen using our proposed Bloch sphere approach, without using any matrices multiplication and unitary representations. After transpilation, the final transpiled p-SWAP gate has approximately 23% quantum cost reduction and 26% depth minimization than those of the final transpiled standard SWAP gate.
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CALA-nnn: A Quantum Library for Realizing Cost-Effective 2-, 3-, 4-, and 5-bit Gates on IBM Quantum Computers using Bloch Sphere Approach, Clifford+T Gates, and Layouts
We introduce a new quantum layout-aware approach to realize cost-effective nnn-bit gates using the Bloch sphere, for 2≤n≤52 \le n \le 52≤n≤5 qubits. These nnn-bit gates are entirely constructed from the Clifford+T gates, in the approach of selecting sequences of rotations visualized on the Bloch sphere. This Bloch sphere approach ensures to match the quantum layout for synthesizing (transpiling) these nnn-bit gates into an IBM quantum computer. Various standard nnn-bit gates (Toffoli, Fredkin, etc.) and their operational equivalent of our proposed nnn-bit gates are examined and evaluated, in the context of the final quantum costs, as the final counts of generated IBM native gates. In this paper, we demonstrate that all our nnn-bit gates always have lower quantum costs than those of standard nnn-bit gates after transpilation. Hence, our Bloch sphere approach can be used to build a quantum library of various cost-effective nnn-bit gates for different layouts of IBM quantum computers.
A proposed method for preparing the superposition states of qubits using different axes of the Bloch sphere. This method utilizes the Y-axis of the Bloch sphere using IBM native (square root of X) gates, instead of utilizing the X-axis of the Bloch sphere using IBM non-native Hadamard gates, for transpiling cost-effective quantum circuits on IBM quantum computers. In this paper, our presented method ensures that the final transpiled quantum circuits always have a lower quantum cost than that of the transpiled quantum circuits using the Hadamard gates.