DC SQUID based on the mesoscopic multiterminal Josephson junction

A theory is offered for a novel device, mesoscopic four-terminal SQUID. The studied system consists of a mesoscopic four-terminal junction, one pair of terminals of which is incorporated in a superconducting ring and the other one is connected with a transport circuit. The nonlocal weak coupling between the terminals leads to effects of phase dragging and magnetic flux transfer. The behaviour of a four-terminal SQUID, controlled by the external parameters, the applied magnetic flux and the transport current is investigated. The critical current and the current voltage characteristics as functions of magnetic flux are calculated. In the nonlocal mesoscopic case they depend not only on the magnitude of the applied flux but also on its sign, allowing measurement of the direction of the external magnetic field.Comment: 11 pages, 4 figures, presented at the EUCAS 2001 conferenc

Frustration phenomena in Josephson point contacts between single-band and three-band superconductors

Within the formalizm of Usadel equations the Josephson effect in dirty point contacts between single-band and three-band superconductors is investigated. The general expression for the Josephson current, which is valid for arbitrary temperatures, is obtained. We calculate current-phase relations for very low temperature and in the vicinity of the critical temperature. For three-band superconductors with broken time-reversal symmetry (BTRS) point contacts undergo frustration phenomena with different current-phase relations, corresponding to φ-contacts. For three-band superconductors without BTRS we have close to sinusoidal current-phase relations and absence of the frustration, excepting the case of very low temperature, where under certain conditions two ground states of the point contact are realized. Our results can be used as the potential probe for the detection of the possible BTRS state in three-band superconducting system

Magnetic flux noise in the three Josephson junctions superconducting ring

We analyze the influence of noise on magnetic properties of a superconducting loop which contains three Josephson junctions. This circuit is a classical analog of a persistent current (flux) qubit. A loop supercurrent induced by external magnetic field at the presence of thermal fluctuations is calculated. In order to get connection with experiment we calculate the impedance of the low-frequency tank circuit which is inductively coupled with a loop of interest. We compare obtained results with the results in quantum mode — when the three junction loop exhibits quantum tunneling of the magnetic flux. We demonstrate that the tank-loop impedance in the classical and quantum modes have different temperature dependence and can be easily distinguished experimentally

Josephson currents in point contacts between dirty two-band superconductors

We developed microscopic theory of Josephson effect in point contacts between dirty two-band superconductors. The general expression for the Josephson current, which is valid for arbitrary temperatures, is obtained. This expression was used for calculation of current-phase relations and temperature dependences of critical current with application to MgB₂ superconductor. Also we have considered influence on contact characteristics interband scattering effect appeared in case of dirty superconductors. It is shown that the correction to Josephson current due to the interband scattering depends on phase shift in the banks (i.e.,s- or s±-wave symmetry of order parameters)

Igor Orestovich Kulik To the 75th birthday anniversary

Igor Orestovich Kulik — a prominent physicist and an outstanding representative of Kharkov’s school of theoretical physics, Corresponding member of the National Academy of Sciences of Ukraine and Ukrainian State Prize Laureate — will be 75 on November 19 this year

Resonant effects in the strongly driven phase-biased Cooper-pair box

We study the time-averaged upper level occupation probability in a strongly driven two-level system, particularly its dependence on the driving amplitude x₀ and frequency ω and the energy level separation ∆E. In contrast to the case of weak driving (x₀ ≪ ∆E), when the positions of the resonances almost do not depend on x₀, in the case of the strong driving (x₀ ~ ∆E) their positions are strongly amplitude dependent. We study these resonances in the concrete system — the strongly driven phase-biased Cooper-pair box, which is considered to be weakly coupled to the tank circuit

Coherent current states in a two-band superconductor

Homogeneous current states in thin films and Josephson current in superconducting microbridges are studied within the frame of a two-band Ginzburg–Landau theory. By solving the coupled system of equations for two order parameters the depairing current curves and Josephson current-phase relation are calculated for different values of phenomenological parameters and . Coefficients and describe the coupling of order parameters (proximity effect) and their gradients (drag effect), respectively. For definite values of parameters the dependence of current j on superfluid momentum q contains local minimum and corresponding bi-stable states. It is shown that the Josephson microbridge from two-band superconductor can demonstrate -junction behavior

Dynamic behavior of superconducting flux qubit excited by a series of electromagnetic pulses

We study theoretically the behavior of the superconducting flux qubit subjected to the series of the electromagnetic pulses. The possibility of controlling the system state via changing the parameters of the pulse is studied. We calculated the phase shift in the tank circuit weakly coupled to the qubit which can be measured by the impedance measurement technique. For the flux qubit we consider the possibility to estimate relaxation rate from the impedance measurements by varying the delay time between the pulses

Ballistic Four-Terminal Josephson Junction: Bistable States and Magnetic Flux Transfer

The macroscopic quantum interference effects in ballistic Josephson microstructures are investigated. The studied system consists of four bulk superconductors (terminals) which are weakly coupled through the mesoscopic rectangular normal metal (two dimensional electron gas). We show that nonlocal electrodynamics of ballistic systems leads to specific current-phase relations for the mesoscopic multiterminal Josephson junction. The nonlocal coupling of supercurrents produces the "dragging" effect for phases of the superconducting order parameter in different terminals. The composite Josephson junction, based on this effect, exhibits the two -level system behaviour controlled by the external magnetic flux. The effect of magnetic flux transfer in a system of nonlocally coupled superconducting rings is studied.Comment: 12pages LaTex, 6 figures; e-mail: [email protected]