We show that two capacitively coupled Josephson junctions, in the quantum limit, form a simple coupled qubit system with effective coupling controlled by the junction bias currents. We compute numerically the energy levels and wave functions for the system, and show how these may be tuned to make optimal qubits. The dependence of the energy levels on the parameters can be measured spectroscopic...

A zigzag boundary between a dx2−y2 and an s-wave superconductor is believed to behave like a long Josephson junction with alternating sections of 0 and π symmetry. We calculate the field-dependent critical current of such a junction, using a simple model. The calculation involves discretizing the partial differential equation for the phase difference across a long 0-π junction. In this form, th...

The fundamental noise limit of a phase-preserving amplifier at frequency [Formula: see text] is the standard quantum limit [Formula: see text]. In the microwave range, the best candidates have been amplifiers based on superconducting quantum interference devices (reaching the noise temperature [Formula: see text] at 700 MHz), and non-degenerate parametric amplifiers (reaching noise levels close...

We present switching current measurements in niobium-aluminum oxideniobium underdamped Josephson rings. Underdamped Josephson rings display hysteretic current-voltage curves which can be characterized by their switching current, the value of applied current at which the junctions switch to the energy-gap voltage. The value of the switching current is strongly affected by temperature and by the ...

We demonstrate a zero-crossing Shapiro step generated in a magnetically-coupled Josephson gate, where a long Josephson junction and a control line are placed in-line. The operation is based on the imbalanced evolution of the junction phases owing to the different amplitudes of the positive and negative critical current. A test circuit was fabricated using a Nb/AlOx/Nb junction technology. When ...

We report on a nontrivial type of slow-fast dynamics in a Josephson junction model externally shunted by a resistor and an inductor. For large values of the shunt inductance the slow manifold is highly folded, and different types of dynamical behavior in the fast variable are possible in dependence on the other parameters of the junction. We discuss how particular features of the dynamics are m...

We have investigated the influence of shot noise on the IV curves of a single mesoscopic Josephson junction. We observe a linear enhancement of zero-bias conductance of the Josephson junction with increasing shot-noise power. Moreover, the IV curves become increasingly asymmetric. Our analysis on the asymmetry shows that the Coulomb blockade of Cooper pairs is strongly influenced by the non-Gau...

A new current-injection Josephson latch employing a single-flux quantum is proposed. It has a master-slave circuit configuration and operates under ac power supply. In the circuit, data are stored as a circulating current in a superconducting loop consisting of a single junction and inductances. A two-junction interferometer gate directly coupled to the l.oop reads out the stored data. Dual-rai...

A controllable p-SQUID is a DC SQUID ~direct-current superconducting quantum interference device! with two controllable p junctions as weak links. A controllable p junction consists of a superconducting–normal metal–superconducting Josephson junction with two additional contacts to the normal region of the junction. By applying a voltage Vc over these contacts it is possible to control the stat...