Fluctuation and Noise Letters

It is argued that the existing schemes of fault-tolerant quantum computation, designed for discrete time models and based on quantum error correction, fail for continuous time Hamiltonian models, even with Markovian noise.

We present additional considerations to elucidate the nature of Cohen's classical teleportation of classical bits.

In response to a recently published protocol for classical teleportation of classical states [1], Hrasko [2] has made some remarks in connection with the impossibility of precise quantum teleportation if a classical mixture is used in place of the EPR state, and with regard to the epistemological interpretation of quantum states. The purpose of this note is to attempt to clarify these issues and their relevance for the argumentation presented in [1].

Following the victory of the Congress Party, the Indian SENSEX index crashed in May 2004. We present a brief analysis of the crash, showing that very likely the crash was due to the outcome of the Indian elections, but in a situation of very high instability, with the market already past a transition point, well described by the Sornette-Johansen model.

A method for increasing the specificity of an MR image using noise correlation measurements is presented. From an MR image different regions within the body are identified based on contrast. Noise signals measured at the ports of the experimental setup are functions of the conductivity at each region and the sensitivity map of the field probes. For a simulated sensitivity map, the ratio of conductivities of two regions of a phantom containing saline and distilled water was determined from the measured noise correlation at the ports.

The motion of elastically coupled Brownian particles in ratchet-like potentials has attracted much recent interest due to its application to transport processes in many fields, including models of DNA polymers. We consider the influence of the type of interacting force on the transport of two particles in a one-dimensional flashing ratchet. Our aim is to examine whether the common assumption of elastic coupling captures the important features of ratchet transport when the inter-particle forces are more complex. We compare Lennard-Jones type interaction to the classical case of elastically coupled particles. Numerical simulations agree with analytical formulas for the limiting cases where the coupling is very weak or very strong. Parameter values where the Lennard-Jones force is not well approximated by a linearization of the force about the equilibrium distance are identified.

The effect of additive Gaussian noise on the chaos-suppression scenario of a broad and important family of dissipative nonautonomous systems subjected to chaos-suppressing excitations is investigated by means of Melnikov's method. The analysis indicates that the optimal suppressory initial phase differences between the chaos-inducing and chaos suppressing forcing terms remain the same as in the purely deterministic case, while the ranges of suppressory initial phase differences and amplitudes narrow as noise strenght is increased from zero. Computer simulations of a two-well Duffing oscillator confirm the theoretical predictions.

We report measurements and analysis of the voltage noise due the to vortex motion, performed in superconducting Niobium micro-bridges. Noise in such small systems exhibits important changes from the behavior commonly reported in macroscopic samples. In the low biasing current regime, the voltage fluctuations are shown to deviate substantially from the Gaussian behavior which is systematically observed at higher currents in the so called flux-flow regime. The responsibility of the spatial inhomogeneities of the critical current in this deviation from Gaussian behavior is emphasized. We also report on the first investigation of the effect of an artificial pinning array on the voltage noise statistics. It is shown that the fluctuations can lose their stationarity, and exhibit a Lévy flight-like behavior.

The requirement of phase noise imposed on the stable local oscillator for bistatic synthetic aperture radar (SAR) is much more severe than in the monostatic cases. So accurate phase noise simulation is of great importance during the design and development of bistatic SAR systems. This letter concentrates on the impacts of limited oscillator stability between bistatic transmitter and receiver, and presents an analytical model of phase noise that solves some drawbacks implicitly present in the previously proposed models. This model uses the Gaussian noise as the input of a hypothetical low-pass filter and its output is then considered as phase noise. Finally, some simulation results are provided to demonstrate the validity of this model.

The time dynamics of long-term time series of satellite thermal signal, measured at Mount Etna, has been investigated. The signal has been analyzed by means of a recently proposed multi-temporal and robust technique (RST), which has already shown to be better capable to detect and monitor volcanic hotspots, compared to traditional satellite approaches. The temporal fluctuations of the thermal signal detected by RST over a long series (1995-2005) of Advanced Very High Resolution Radiometer (AVHRR) satellite data, have been characterized by means of the correlation function and the power spectrum analysis, which have shown the presence of correlation structures in the thermal time series recorded in the crater area.

Ultra-wideband technology uses baseband transmission of low-power ultra-short information-bearing impulses, and represents a promising approach for very-high speed wireless communications with multiple access, as well as for low-rate high-accuracy positioning systems. The first demonstrations of the huge potential of ultra-wideband were based on hypotheses of perfect power control and multiuser interferences modeled as white Gaussian noise. Here, by explicitly modeling the interference with an external impulse signal, we demonstrate the possibility of improving the rejection of the interferer thanks to a constructive action of the noise. This is interpreted as a novel instance of the phenomenon of stochastic resonance or improvement by noise in signal processing.

The effects of hot carrier stress on CMOS voltage-controlled oscillators (VCO) are investigated. A model of the threshold voltage degradation in MOSFETs due to hot carrier stress has been used to model jitter in voltage-controlled oscillators. The relation between the stress time which induces the hot carrier effects due to generation of interface traps near the drain of the n-MOSFETs, and the degradation of the VCO performance is presented. The VCO performance degradation takes into consideration decrease in operation frequency and increase in jitter. The experimental circuits have been designed in 0.5 μm n-well CMOS technology for operation at 3 V. Experimental results show that after four hours hot-carrier stress the jitter is increased by 40 ps for single-ended current starved VCOs.

A historical overview is given on the basic results which appeared by the year 1926 concerning Einstein's fluctuation formula of black-body radiation, in the context of light-quanta and wave-particle duality. On the basis of the original publications – from Planck's derivation of the black-body spectrum and Einstein's introduction of the photons up to the results of Born, Heisenberg and Jordan on the quantization of a continuum – a comparative study is presented on the first lines of thoughts that led to the concept of quanta. The nature of the particle-like fluctuations and the wave-like fluctuations are analysed by using several approaches. With the help of classical probability theory, it is shown that the infinite divisibility of the Bose distribution leads to the new concept of classical "poissonian photo-multiplets" or to the "binary photo-multiplets" of fermionic character. As an application, Einstein's fluctuation formula is derived as a sum of fermion type fluctuations of the binary photo-multiplets.