High-fidelity gates in Josephson phase qubits

Complex algorithms for a quantum computer will require error correction, which calls for logic gates with fidelity below a fault tolerant threshold. We present significant progress towards this goal with our detailed measurements of gate fidelity. We carefully separate out gate and measurement error and construct a complete error budget to demonstrate single qubit gate fidelities of 0.98, limited by energy relaxation. We introduce a new metrology tool `a Ramsey interference error filter' that can measure the excited two-state population down to 10$^{-4}$, a magnitude near the fault tolerant threshold. This measurement demonstrates that our quantum system remains in the two-state qubit manifold during our single qubit operations. This precision and accuracy is made possible by custom control electronics that can create arbitrarily shaped microwave pulses.