Josephson Junctions In Presence Research Articles

Dynamics of coupled sine–Gordon equations: Inductively stacked long Josephson junctions with heterogeneous drives

The article presents the systematic study of the stacked long Josephson junctions in presence of different magnetic inductances. The coupled sine–Gordon equation along with a phase-shift formation is considered to study localized modes in stacks. The asymptotic analysis is applied to investigate analytically the nonlinear amplitude equations by using the spatially continuous and discrete spectrums. It is observed that in the absence of external drives, the system decays exponentially in the case of both strong and weak magnetic inductance, where the synchronized oscillations are obtained. However, in the presence of AC-drive, the system oscillates synchronically and goes to a stable state after a long time. It is revealed that, when the parametric drives are applied, the system decays exponentially in the existence of small driving amplitude. However, when the driving amplitude is large enough, the system oscillates for an infinitely long time.

Temporal non-equilibrium dynamics of a Bose–Josephson junction in presence of incoherent excitations

The time-dependent non-equilibrium dynamics of a Bose–Einstein condensate (BEC) typically generates incoherent excitations out of the condensate due to the finite frequencies present in the time evolution. We present a detailed derivation of a general non-equilibrium Greenʼs function technique that describes the coupled time evolution of an interacting BEC and its single-particle excitations in a trap, based on an expansion in terms of the exact eigenstates of the trap potential. We analyze the dynamics of a Bose system in a small double-well potential with initially all particles in the condensate. When the trap frequency is larger than the Josephson frequency, , the dynamics changes at a characteristic time, , abruptly from the slow Josephson oscillations of the BEC to fast Rabi oscillations driven by quasiparticle excitations in the trap. For times , the Josephson oscillations are undamped, in agreement with the experiments. We analyze the physical origin of the finite scale as well as its dependence on the trap parameter Δ.

Josephson junctions as detectors for non-Gaussian noise

Non-Gaussian fluctuations of the electrical current can be detected with a Josephson junction placed on-chip with the noise source. We present preliminary measurements with an NIS junction as a noise source, and a Josephson junction in the thermal escape regime as a noise detector. It is shown that the Josephson junction detects not only the average noise, which manifests itself as an increased effective temperature, but also the noise asymmetry. A theoretical description of the thermal escape of a Josephson junction in presence of noise with a non-zero third cumulant is presented, together with numerical simulations when the noise source is a tunnel junction with Poisson noise. Comparison between experiment and theory is discussed.

Josephson junctions as detectors for non‐Gaussian noise*

AbstractNon‐Gaussian fluctuations of the electrical current can be detected with a Josephson junction placed on‐chip with the noise source. We present preliminary measurements with an NIS junction as a noise source, and a Josephson junction in the thermal escape regime as a noise detector. It is shown that the Josephson junction detects not only the average noise, which manifests itself as an increased effective temperature, but also the noise asymmetry. A theoretical description of the thermal escape of a Josephson junction in presence of noise with a non‐zero third cumulant is presented, together with numerical simulations when the noise source is a tunnel junction with Poisson noise. Comparison between experiment and theory is discussed.

Field-induced superconductor to insulator transition and phase diagram of Josephson-junction ladders

The superconductor to insulator transition is studied in a self-charging model for a ladder of Josephson-junctions in presence of an external magnetic field. Path integral Monte Carlo simulations of the equivalent (1+1)-dimensional classical model are used to study the phase diagram and critical behavior of the field-induced transition. The phase diagram shows an intervening insulating phase separating the (vortex-free) superconducting phase at low fields from the vortex phases at higher fields. A finite-size scaling analysis shows that the field-induced superconducting to insulator transition is in the KT universality class.

Mutual inductance effects in rf driven planar Josephson junctions arrays

In this paper we investigate the behavior of moderate size two-dimensional classical arrays of Josephson junctions in presence of an external oscillating field. We have included in the model the effects due to mutual inductance terms, and we have employed an explicit set of differential equations. We have found that the discretization parameter βL - i.e. the coupling term due to the inductance of the loops - is the most important parameter to determine the height of the Shapiro steps for a given amplitude and frequency of the rf-bias. The amplitude of the Shapiro steps in the case of zero frustration as a function of the coupling term shows a remarkable minimum for intermediate values when we retain all terms of the full model with mutual inductances, while the limits for very large and very small values of βL they are the same of the single Josephson junction. For the case of frustration 1/2 the Shapiro step becomes smaller in the rigid limit (i.e., small βL as expected for the XY model, and tends to the limit value of the single junctions for the decoupled case (i.e., large βL).

Replica theory and large-D Josephson junction hypercubic models

We study the statistical mechanics of a $D$-dimensional array of Josephson junctions in presence of a magnetic field on a lattice of side $2$. In the high temperature region the thermodynamical properties can be computed in the limit $D \to \infty$. A conjectural form of the thermodynamic properties in the low temperature phase is obtained by assuming that they are the same of an appropriate spin glass system, based on quenched disordered couplings. Numerical simulations show that this conjecture is very accurate in one regime of the magnetic field, while it is probably slightly inaccurate in a second regime.

D-dimensional arrays of Josephson junctions, spin glasses and q-deformed harmonic oscillators

We study the statistical mechanics of a $D$-dimensional array of Josephson junctions in presence of a magnetic field. In the high temperature region the thermodynamical properties can be computed in the limit $D \to \infty$, where the problem is simplified; this limit is taken in the framework of the mean field approximation. Close to the transition point the system behaves very similar to a particular form of spin glasses, i.e. to gauge glasses. We have noticed that in this limit the evaluation of the coefficients of the high temperature expansion may be mapped onto the computation of some matrix elements for the $q$-deformed harmonic oscillator.