Protecting superconducting qubits with a universal quantum degeneracy point

Low-frequency noise can induce serious decoherence in superconducting qubits. Due to its diverse physical origins, such noise can couple with the qubits either as transverse or as longitudinal noise. Here we present a universal quantum degeneracy point approach that can protect an encoded qubit from arbitrary low-frequency noise. We further show that universal quantum logic gates can be performed on the encoded qubits with high fidelity. The proposed scheme can be readily implemented with superconducting flux qubits or with a qubit coupling with a superconducting resonator. Meanwhile, the scheme is also robust against small parameter spreads due to errors of fabrication in the superconducting systems. (paper)