Short-time decoherence of a quantum Hadamard gate with Josephson charge qubits

We investigate the short-time decoherence of a quantum Hadamard gate with the Josephson-junction device (JJD). It is shown that the maximum norm of the deviation operator has the same expression as in the previous literature. We demonstrate that the elementary gate operation can be completed under the low decoherence criterion no matter what the initial state is. Thus, the JJD can be a good candidate of quantum computating devices