Influence of anharmonic and frustration effects on the Josephson flux qubit spectrum

This paper is devoted to investigation of the Josephson flux qubits spectrum taking into account anharmonic current-phase relation of the junction. Changing of the energy spectrum in flux qubits based on single-band/multiband Josephson junctions is also analyzed. It was shown that the presence of anharmonicity and frustration effects in junction leads to changing effective plasma frequency for the different inductance of superconducting ring and, as a result, to the energy spectrum of the qubit.