Implementation of Conditional Phase Gates Based on Tunable ZZ Interactions

Quantum computers, which have the capability to outperform classical computers on specific computational tasks, heavily rely on high-performance two-qubit gates for the realization of quantum algorithms.  In superconducting circuits, two-qubit gates are typically based on a transversal qubit-qubit coupling, implemented either by rf-control or the in-situ frequency tunability of computational qubits.

In this work, we demonstrate a novel approach using a tunable cross-Kerr-type ZZ interaction between two qubits which we realize with a flux-tunable coupler element.
This approach ensures direct control of the acquired conditional phase, without relying on excitation transfer or sideband transitions, and thus features an inherent resilience to leakage and cross talk, both major concerns in the light of recent progress towards full-scale quantum error correction. Additionally it innately enables the realization of continuous gate sets, highly beneficial for near-term variational quantum algorithms. A simple control paradigm and robust performance ensure easy scalability and high compatibility with existing platforms.

PRL paper on Implementation of Conditional Phase Gates