Universal quantum computing with a multi-qubit device with untunable always-on coupling*

We present a method to implement universal one-bit and two-bit quantum logical gates in a two-qubit device with fixed always-on coupling. In this method the one-bit gate is decomposed into two conditional two-bit gates that are implemented by local manipulations similar to those for the two-bit gates. We demonstrate, by implementing one-bit NOT gate and creating Bell states, that this method can be realized in rf-driven inductively coupled two SQUID flux qubits with realistic device parameters. This method is simple, does not need any additional hardware resources, and can be readily extended to multi-qubit logical gates required for scalable quantum computation.