We have considered relativistic soliton dynamics governed by the sine-Gordon equation and affected by short spatial inhomogeneities of the driving force and thermal noise. Developed analytical and numerical methods for calculation of soliton scatteri
ng at the inhomogeneities allowed us to examine the scattering as a measurement tool for sensitive detection of polarity of the inhomogeneities. We have considered the superconducting fluxonic ballistic detector as an example of the device in which the soliton scattering is utilized for quantum measurements of superconducting flux qubit. We optimized the soliton dynamics for the measurement process varying the starting and the stationary soliton velocity as well as configuration of the inhomogeneities. For experimentally relevant parameters we obtained the signal-to-noise ratio above 100 reflecting good practical usability of the measurement concept.
The thermal jitter of transmission of magnetic flux quanta in long Josephson junctions is studied. While for large-to-critical damping and small values of bias current the physically obvious dependence of the jitter versus length $sigmasimsqrt{L}$ is
confirmed, for small damping starting from the experimentally relevant $alpha=0.03$ and below strong deviation from $sigmasimsqrt{L}$ is observed, up to nearly complete independence of the jitter versus length, which is exciting from fundamental point of view, but also intriguing from the point of view of possible applications.
We analyze a two-level quantum system, describing the phase qubit, during a single-pulse readout process by a numerical solution of the time-dependent Schroedinger equation. It has been demonstrated that the readout error has a minimum for certain va
lues of the system`s basic parameters. In particular, the optimization of the qubit capacitance and the readout pulse shape leads to significant reduction of the readout error. It is shown that in an ideal case the fidelity can be increased to almost 97% for 2 ns pulse duration and to 96% for 1 ns pulse duration.
The computer simulations of the process of single pulse readout from the flux-biased phase qubit is performed in the frame of one-dimensional Schroedinger equation. It has been demonstrated that the readout error can be minimized by choosing the opti
mal pulse duration and the depth of a potential well, leading to the fidelity of 0.94 for 2ns and 0.965 for 12ns sinusoidal pulses.
We study the transient statistical properties of short and long Josephson junctions under the influence of thermal and correlated fluctuations. In particular, we investigate the lifetime of the superconductive metastable state finding the presence of
noise induced phenomena. For short Josephson junctions we investigate the lifetime as a function both of the frequency of the current driving signal and the noise intensity and we find how these noise-induced effects are modified by the presence of a correlated noise source. For long Josephson junctions we integrate numerically the sine-Gordon equation calculating the lifetime as a function of the length of the junction both for inhomogeneous and homogeneous bias current distributions. We obtain a nonmonotonic behavior of the lifetime as a function of the frequency of the current driving signal and the correlation time of the noise. Moreover we find two maxima in the nonmonotonic behaviour of the mean escape time as a function of the correlated noise intensity.
We present the analysis of the mean switching time and its standard deviation of short overdamped Josephson junctions, driven by a direct current and a periodic signal. The effect of noise enhanced stability is investigated. It is shown that fluctuat
ions may both decrease and increase the switching time.
We present the analysis of the mean switching time and its standard deviation of an overdamped Josephson junction, driven by a direct current and a single flux quantum (SFQ) pulse. The performed analysis allows to find the optimal value of the bias c
urrent of the clock generator, responsible for the shape of SFQ pulse, which minimizes noise-induced switching errors.
The influence of fluctuations and periodical driving on temporal characteristics of short overdamped Josephson junction is analyzed. We obtain the standard deviation of the switching time in the presence of a dichotomous driving force for arbitrary n
oise intensity and in the frequency range of practical interest. For sinusoidal driving the resonant activation effect has been observed. The mean switching time and its standard deviation have a minimum as a function of driving frequency. As a consequence the optimization of the system for fast operation will simultaneously lead to minimization of timing errors.
This paper presents the analytical and numerical analysis of fluctuational dynamics of ac hysteretic SQUID. It has been demonstrated, that the most important parameter for the improvement of the hysteretic SQUID sensitivity is the ratio between the p
ump and the characteristic frequencies but not their absolute values. The resonant behavior of signal-to-noise ratio as function of the pump frequency has been observed and the narrow area for the optimal pump frequency range is indicated.
