Nearest-Neighbor and Fault-Tolerant Quantum Circuit Implementation

The quest of achieving higher computing performance is driving the research on quantum computing, which is reporting new milestones almost on a daily basis. For practical quantum circuit design, fault tolerance is an essential condition. This is achieved by mapping the target functions into the Clifford+T group of elementary quantum gates. Furthermore, the application of error-correcting codes in quantum circuits requires the quantum gates to be formed between adjacent Qubits. In this work, we improve the state-of-the-art quantum circuit design by addressing both of the above challenges. First, we propose a novel mapping of Multiple-Control Toffoli (MCT) gates to Clifford+T group gates, which achieves lower gate count compared to earlier work. Secondly, we show a generic way to convert any Clifford+T circuit into a nearest neighbor one. We validate the efficacy of our approach with detailed experimental studies.