Quantum phase slips in the presence of finite-range disorder

To study the effect of disorder on quantum phase slips (QPSs) in superconducting wires, we consider the plasmon-only model where disorder can be incorporated into a first-principles instanton calculation. We consider weak but general finite-range disorder and compute the form factor in the QPS rate associated with momentum transfer. We find that the system maps onto dissipative quantum mechanics, with the dissipative coefficient controlled by the wave (plasmon) impedance Z of the wire and with a superconductor-insulator transition at Z = 6.5 k. We speculate that the system will remain in this universality class after resistive effects at the QPS core are taken into account.     

Suppression of superconductivity in disordered interacting wires

We study superconductivity suppression due to thermal fluctuations in disordered wires using the replica nonlinear sigma-model (NLsigmaM). We show that in addition to the thermal phase slips there is another type of fluctuations that result in a finite resistivity. These fluctuations are described by saddle points in NLsigmaM and cannot be treated within the Ginzburg-Landau approach. The contribution of such fluctuations to the wire resistivity is evaluated with exponential accuracy. The magnetoresistance associated with this contribution is negative.     

Evidence for macroscopic quantum tunneling of phase slips in long one-dimensional superconducting Al wires

Quantum phase slips have received much attention due to their relevance to superfluids in reduced dimensions and to models of cosmic string production in the early universe. Their establishment in one-dimensional superconductors has remained controversial. Here we study the nonlinear current-voltage characteristics and linear resistance in long superconducting Al wires with lateral dimensions approximately 5 nm. We find that, in a magnetic field and at temperatures well below the superconducting transition, the observed behaviors can be described by the nonclassical, macroscopic quantum tunneling of phase slips, and are inconsistent with the thermal activation of phase slips.     

Experimental characterization of the transition to phase synchronization of chaotic CO2 laser systems

We investigate the transition route to phase synchronization in a chaotic laser with external modulation. Such a transition is characterized by the presence of a regime of periodic phase synchronization, in which phase slips occur with maximal coherence in the phase difference between output signal and external modulation. We provide the first experimental evidence of such a regime and demonstrate that it occurs at the crossover point between two different scaling laws of the intermittent-type behavior of phase slips.     

Universal conductance of nanowires near the superconductor-metal quantum transition

We consider wires near a zero temperature transition between superconducting and metallic states. The critical theory obeys hyperscaling, which leads to a universal frequency, temperature, and length dependence of the conductance; quantum and thermal phase slips are contained within this critical theory. Normal, superconducting, and mixed (SN) leads on the wire determine distinct universality classes. For the SN case, wires near the critical point have a universal dc conductance which is independent of the length of the wire at low temperatures.     

Sharp superconductor-insulator transition in short wires

Recent experiments on short MoGe nanowires show a sharp superconducting-insulating transition at the universal resistance R(Q)=h/(4e(2)), contrary to the expectation of a smooth temperature dependence of the resistance for such Josephson-like systems. We present a self-consistent renormalization-group treatment of interacting quantum phase slips in short superconducting wires, which reproduces this sharp universal transition. Our method should also apply to other systems in the sine-Gordon universality class, in the previously inaccessible intermediate-coupling regime.     

Observation of chirped soliton dynamics at lambda = 1.55 microm in a single-mode optical fiber with frequency-resolved optical gating

We present an experimental observation of the dynamics of an initially chirped optical soliton at 1.55microm that is propagating through a single-mode optical fiber, using frequency-resolved optical gating (FROG). FROG permits observation of both the amplitude and the phase profiles of ultrashort pulses, providing complete information on the pulse evolution. The features that are detected, which include what is believed to be the first experimental observation of phase slips, are in quantitative agreement with numerical simulations that employ the nonlinear Schr?dinger equation.     

Robustness of the noise-induced phase synchronization in a general class of limit cycle oscillators

We show that a wide class of uncoupled limit-cycle oscillators can be in-phase synchronized by common weak additive noise. An expression of the Lyapunov exponent is analytically derived to study the stability of the noise-driven synchronizing state. The result shows that such a synchronization can be achieved in a broad class of oscillators with little constraint on their intrinsic property. On the other hand, the leaky integrate-and-fire neuron oscillators do not belong to this class, generating intermittent phase slips according to a power law distribution of their intervals.     

External control of a metal-insulator transition in GaMnAs wires

Quantum transport in disordered ferromagnetic (III,Mn)V semiconductors is studied theoretically. Mesoscopic wires exhibit an Anderson disorder-induced metal-insulator transition that can be controlled by a weak external magnetic field. This metal-insulator transition should also occur in other materials with large anisotropic magnetoresistance effects. The transition can be useful for studies of zero-temperature quantum critical phase transitions and fundamental material properties.     

Stochastic phase dynamics and noise-induced mixed-mode oscillations in coupled oscillators

Synaptically coupled neurons show in-phase or antiphase synchrony depending on the chemical and dynamical nature of the synapse. Deterministic theory helps predict the phase differences between two phase-locked oscillators when the coupling is weak. In the presence of noise, however, deterministic theory faces difficulty when the coexistence of multiple stable oscillatory solutions occurs. We analyze the solution structure of two coupled neuronal oscillators for parameter values between a subcritical Hopf bifurcation point and a saddle node point of the periodic branch that bifurcates from the Hopf point, where a rich variety of coexisting solutions including asymmetric localized oscillations occurs. We construct these solutions via a multiscale analysis and explore the general bifurcation scenario using the lambda-omega model. We show for both excitatory and inhibitory synapses that noise causes important changes in the phase and amplitude dynamics of such coupled neuronal oscillators when multiple oscillatory solutions coexist. Mixed-mode oscillations occur when distinct bistable solutions are randomly visited. The phase difference between the coupled oscillators in the localized solution, coexisting with in-phase or antiphase solutions, is clearly represented in the stochastic phase dynamics.     

Excitation of surface electromagnetic waves at an anisotropically conducting vacuum-metamaterial interface by the attenuated total internal reflection method

The excitation of well-localized oblique surface waves above the surface of a dielectric with a one-dimensional array of perfectly conducting wires is studied theoretically using the attenuated total internal reflection method. It is assumed that the distance between the wires and their diameter are much smaller than the surface wavelength. The frequencies of excited surface waves are much lower than the plasma frequency of the metal, and their electric field is orthogonal to the wires. It is shown that such surface waves can be excited with the help of a homogeneous TM wave as well as with the help of a homogeneous wave with an electric field polarized perpendicularly to the wires. It is found that in the course of excitation of oblique waves, the incident TM wave is partly polarized into a wave of the TE type.     

Superconducting fluctuation induced conductance corrections near a pair-breaking quantum phase transition in doubly connected ultrathin cylinders of Al

We report measurements on ultrathin,doubly connected superconducting cylinders of Al that exhibit a destructive regime,which refers to the loss of superconductivity in a doubly connected superconductor near applied half flux quanta due to the sample topology and the small size of the sample.A depairing quantum phase transition(QPT)between a superconducting and metallic state tuned by the magnetic flux enclosed in the quasi one-dimensional(1D)cylinder was found at the onset of the destructive regime.Results on magnetic flux and temperature dependent sample resistance as well as current-voltage characteristics revealed the presence of both thermally activated and quantum phase slips near the depairing QPT.On the superconducting side of the QPT,thermally activated phase slips as described by the Langer-Ambegaokar and McCumber-Halperin(LAMH)theory were found to describe the sample resistance as the system was pushed towards the QPT by a magnetic field applied along the cylinder axis.However,deviation from this behavior was found at low temperatures,signaling the presence of the quantum phase slips.Most importantly,we observed a highly unusual negative slope in the resistance versus temperature curves on the metallic side of the QPT as predicted by the diagrammatic calculation of the dc conductivities in a 1D system near a depairing QPT.Our work suggests that fluctuations from both the phase and the amplitude of the superconducting order parameter are important for the superconductor-to-metal depairing QPT.     

Correlation method estimation of the modulation signal in the weak equivalence principle test

In a test of the weak equivalence principle(WEP) with a rotating torsion pendulum, it is important to estimate the amplitude of the modulation signal with high precision. We use a torsional filter to remove the free oscillation signal and employ the correlation method to estimate the amplitude of the modulation signal. The data analysis of an experiment shows that the uncertainties of amplitude components of the modulation signal obtained by the correlation method are in agreement with those due to white noise. The power spectral density of the modulation signal obtained by the correlation method is about one order higher than the thermal noise limit. It indicates that the correlation method is an effective way to estimate the amplitude of the modulation signal and it is instructive to conduct a high-accuracy WEP test.     

Twist effect on hysteresis loss in Bi2223 multifilamentary wires exposed to an AC magnetic field

We fabricated Bi2223 multifilamentary sample wires with various twist pitches and investigated the electromagnetic properties experimentally. They showed monofilamentlike electromagnetic properties regardless of twisting due to the contacts among filaments and/or proximity effect. The observed AC losses in the non-twisted sample wire agreed roughly with the theoretical prediction for a homogeneous superconducting slab with the same thickness of the filamentary region on the basis of Irie–Yamafuji model. However the AC losses in the twisted wires deviated from the theoretical ones, especially for the amplitude around the theoretically predicted penetration field of the slab. We showed that the observed AC loss properties can be explained by both the twist effect for the macroscopic shielding current and the contribution of the local shielding current.     

The effect of dispersive and non-dispersive channels on time delay estimation

The cepstrum and complex demodulation for both wrapped and unwrapped phase outputs are examined as to their performance in the presence of amplitude distortion and dispersion in a channel. With amplitude distortion, complex demodulation is a more powerful processor than cepstrum unless zeros occur in the amplitude spectrum of the distortion. Such singularities disrupt the unwrapped phase output completely and, unless removed, limit the useful region of the wrapped phase output. With phase distortion or dispersion, both the cepstrum and complex demodulation (wrapped phase output) yield biased time delay estimates. A successful phase unwrapping process in complex demodulation enables the correct estimate of the time delay in the presence of dispersion. In addition, the dispersion itself is extracted.     

Model of a proposed superconducting phase slip oscillator: a method for obtaining few-photon nonlinearities

We theoretically investigate a driven oscillator with the superconducting inductance subject to quantum phase slips (QPS). We find uncommon nonlinearities in the proposed device: they oscillate as a function of the number of photons N with a local period of the order of √N. We prove that such nonlinearities result in multiple metastable states encompassing few photons and study oscillatory dependence of various responses of the oscillator. Such nonlinearities enable new possibilities for quantum manipulation of photon states and very sensitive measurements to confirm the coherence of phase slips.     

A 45° PROTOTYPE OF THE CENTRAL DRIFT CHAMBER FOR BES AND RESULTS OF COSMIC RAY TEST

It is described that the function,structure, amplitude characteristics and results of cosmic ray test of a prototype of the central drift chamber for Beijing Spectrometer (BES). It was found that if appropriate high voltage is applied on the field wires homogeneous signal amplitude from different Layer of the chamber can be obtained. The drift velocity deduced by track reconstruction is 5.3cm/μs. The spatial resolution is about 134μm.     

Generation of ionospheric irregularities upon propagation of solitary internal gravity wave during the major magnetic storm of October 29–31, 2003

Using the technique of global detection of ionospheric disturbances, based on processing the data of the global GPS-receiver network, we obtain experimental proof of the existence of a solitary wave (soliton) in the atmosphere during the main phase of the major magnetic storm of October 30, 2003. The soliton with a characteristic duration of about 40 min and a relative amplitude of up to 40%, originated at the moment of the maximum disturbance of the Earth’s magnetic field, traveled without changing its shape at a distance of up to 4500 km with a velocity of 1400 m/s, which exceeded the atmospheric sound velocity at the heights of the main electron-density maximum in the ionosphere (about 300 km) by a factor of 1.5. The intensity of variations in the total electron content in the period range 1–10 min increases by an order of magnitude as the soliton propagates from the North-East to the South-West of the USA in the regions with the maximum amplitude of the large-scale disturbance. This corresponds to enhancement of ionospheric irregularities with scales from 10 to 100 km, and also of small-scale irregularities (SSI) with scales of 100 to 1000 m, since the spectrum of the ionospheric irregularities has a power-law shape. Spatio-temporal characteristics of the density distribution of phase slips of GPS signals are close to the corresponding characteristics of the SSI intensity. This agrees with the existing concept that the phase slips result from scattering of GPS radio signals by SSIs. Both the SSI amplitude and the density of phase slips decrease as the soliton decays in amplitude. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 2, pp. 89–104, February 2006.     

Persistent current in superconducting nanorings

The superconductivity in very thin rings is suppressed by quantum phase slips. As a result, the amplitude of the persistent current oscillations with flux becomes exponentially small, and their shape changes from sawtooth to a sinusoidal one. We reduce the problem of low-energy properties of a superconducting nanoring to that of a quantum particle in a sinusoidal potential and show that the dependence of the current on the flux belongs to a one-parameter family of functions obtained by solving the respective Schr?dinger equation with twisted boundary conditions.