A simple all-microwave entangling gate for fixed-frequency   superconducting qubits
  We demonstrate an all-microwave two-qubit gate on superconducting qubits which are fixed in frequency at optimal bias points. The gate requires no additional subcircuitry and is tunable via the amplitude of microwave irradiation on one qubit at the transition frequency of the other. We use the gate to generate entangled states with a maximal extracted concurrence of 0.88 and quantum process tomography reveals a gate fidelity of 81%. 
Jerry M. Chow, A. D. Corcoles, Jay M. Gambetta, Chad Rigetti, B. R.   Johnson, John A. Smolin, J. R. Rozen, George A. Keefe,...
quant-ph cond-mat.mes-hall