We introduce a new entangling gate between two fixed-frequency qubits statically coupled via a microwave resonator bus which combines the following desirable qualities: all-microwave control, appreciable qubit separation for reduction of crosstalk and leakage errors, and the ability to function as a two-qubit conditional-phase gate. A fixed, always-on interaction is explicitly designed between higher energy (non-computational) states of two transmon qubits, and then a conditional-phase gate is `activated' on the otherwise unperturbed qubit subspace via a microwave drive. We implement this microwave-activated conditional-phase gate with a fidelity from quantum process tomography of 87%.
@article{arxiv.1307.2594,
title = {Microwave-activated conditional-phase gate for superconducting qubits},
author = {Jerry M. Chow and Jay M. Gambetta and Andrew W. Cross and Seth T. Merkel and Chad Rigetti and M. Steffen},
journal= {arXiv preprint arXiv:1307.2594},
year = {2013}
}