The energy spectrum of a Josephson single-junction quantum bit, qubit with an anharmonic current—phase relationship is studied. The influence of the second harmonic amplitude in the current—phase relationship on the energy difference between qubit states is analyzed.
This study is devoted to the investigation of the Josephson phase qubit spectrum considering the anharmonic current-phase relation of the junction. The change in energy difference in the spectrum of phase qubits based on single-band/multiband Josephson junctions is also analyzed. It was shown that the presence of the anharmonic term in the current-phase relation and frustration effects in the junction electrodes leads to changing effective plasma frequencies in the different cases and results in an energy spectrum.
This paper numerically analyzes the influence of second harmonics on the characteristics of Josephson junction quantum bits (qubits). It is shown that the splitting of energy states of phase qubits is sensitive to energy scale and unharmonicity parameters. On the other hand, for charge qubits, the expectation value of the Cooper-pair number is not affected by the inclusion of unharmonicity parameters, whereas the expectation value of the superconducting current is strongly influenced by energy scale and unharmonicity parameters. The numerical results seem to present the importance of second harmonics in the realization of superconducting qubits.
The aim of this review is the analysis of dynamical properties of Josephson junctions (JJ) with anharmonic current-phase relation (CPR). Firstly, discussion of theoretical foundation of anharmonic CPR in different Josephson structures and their experimental observation are presented. The influence of anisotropy and multiband effects on CPR of JJ are analyzed. We present recent theoretical study results of the anharmonic CPR influence on I–V curve, plasma frequency, and dynamics of long JJ. Results of study of Shapiro steps in I–V curve of anharmonic JJ are also presented. Finally, CPR anharmonicity effect on characteristics of JJ-based qubits is discussed.