arXiv subjects

A. S. Kiyko

Publications and source records attributed to A. S. Kiyko.

3 recordsLinked to original sources

arXiv2015

Josephson systems based on ballistic point contacts between single-band and multi-band superconductors

The Josephson effect in ballistic point contacts between single-band and multi-band superconductors was investigated. It was found that in the case of Josephson junctions formed by a single-band and an $s_\pm$-wave two-band superconductor as well as by a single-band and a three-band superconductor the junctions become frustrated, demonstrating the $ϕ$-contact properties. Depending on the ground state of a three-band superconductor with broken time-reversal symmetry (BTRS), the Josephson junction can have from one to three energy minima, some of which can be locally stable. We also study the behavior of a dc SQUID based on the Josephson junctions between single-band and multi-band superconductors. Some features on the dependences of the critical current and the total magnetic flux on the applied flux of a dc SQUID based on the Josephson point contacts between a single-band superconductor and an $s_\pm$-wave superconductor, three-band superconductor with BTRS and three-band superconductor without BTRS as compared to the conventional dc SQUIDs based on single-band superconductors were found. The results can be used as an experimental tool to detect the existence of multi-band structure and BTRS.

cond-mat.supr-con↗

arXiv2009

Dynamics of Josephson-junction qubits with exactly solvable time-dependent bias pulses

The quantum dynamics of a two-state system (qubit) can be governed by means of external control parameters present in time-dependent bias pulses of special forms. We consider the class of biases for which the time evolution equation without a dissipation can be solved exactly. Concentrating for definiteness on the flux qubit we calculate the probability of the definite direction of the current in the loop and its time-averaged values as functions of the qubit's control parameters both analytically and solving numerically the equation of motion for the density matrix in the presence of relaxation and decoherence. It is shown that there exist such time-dependent biases that the definite current direction probability with no dissipation taken into account becomes a monotonously growing function of time tending to a value which may exceed 1/2. We also calculate the probability to find the system in the excited state and show the possibility of the inverse population in a properly driven two-state system provided the relaxation and dephasing rates are small enough.

quant-ph↗

arXiv2004

Dynamic behaviour of Josephson-junction qubits: crossover between Rabi oscillations and Landau-Zener transitions

We study the dynamic behaviour of a quantum two-level system with periodically varying parameters by solving the master equation for the density matrix. Two limiting cases are considered: multiphoton Rabi oscillations and Landau-Zener transitions. The approach is applied to the description of the dynamics of superconducting qubits. In particular, the case of the interferometer-type charge qubit with periodically varying parameters (gate voltage or magnetic flux) is investigated. The time-averaged energy level populations are calculated as funtions of the qubit's control parameters.

cond-mat.supr-con↗