Switchable Next-Nearest-Neighbor Coupling for Controlled Two-Qubit Operations

Abstract

In a superconducting quantum processor with nearest neighbor coupling, the dispersive interaction between adjacent qubits can result in an effective next-nearest-neighbor coupling for which the strength depends on the state of the intermediary qubit. Here, we theoretically explore the possibility of engineering this next-nearest-neighbor coupling for implementing controlled two-qubit operations where the intermediary qubit controls the operation on the next-nearest neighbor pair of qubits. Specially, in a system comprising two types of superconducting qubits with opposite-sign anharmonicity arranged in an -A-B-A- pattern, where the unwanted static ZZ coupling between adjacent qubits could be heavily suppressed, a switchable coupling between the next-nearest-neighbor qubits can be achieved via the intermediary qubit, for which the qubit state functions as an on/off switch for this coupling. Therefore, depending on the adopted activating scheme, various controlled two-qubit operations such as controlled-iSWAP gate can be realized, potentially enabling circuit depth reductions as to a standard decomposition approach for implementing generic quantum algorithms.