Zero-frequency Noise Research Articles

Probing entanglement and nonlocality of electrons in a double-dot via transport and noise.

Addressing the feasibility of quantum communication with electrons we consider entangled spin states of electrons in a double-dot which is weakly coupled to leads. We show that the entanglement of two electrons in the double-dot can be detected in mesoscopic transport and noise measurements. In the Coulomb blockade and cotunneling regime the singlet and triplet states lead to phase-coherent current and noise contributions of opposite signs and to Aharonov-Bohm and Berry phase oscillations. These oscillations are a genuine two-particle effect and provide a direct measure of nonlocality in entangled states. We show that the ratio of zero-frequency noise to current is equal to the electron charge.

The contrast-detail behaviour of a photostimulable phosphor based computed radiography system

Contrast-detail measurements were performed on a computed radiography imaging system as a function of detector entrance air kerma over the dose range from 0.743 mu Gy (0.085 mR) to 277 mu Gy (31.8 mR). A theoretical model of contrast-detail behaviour for a photostimulable phosphor computed radiography system has been derived, which is based on a modified version of the Rose theory of threshold detection. Included in the model are both system and X-ray quantum noise terms, as well as the response of the eye. The zero-frequency noise power of the computed film images was measured with a double-beam scanning microdensitometer. For a given detector dose, good agreement was found between the predicted and measured data when this measurement of system noise was included in the model. The contrast-detail results obtained for the computed radiography system were also compared with contrast-detail results for an image intensifier-TV based digital imaging system and a conventional film-screen system.

Quantum theory of thermal noises for steady-state hot-electron transport under a strong electric field.

Current fluctuation and thermal noises of an electron system biased at finite electric field E and steady current I are studied. Owing to the separability of the motion of the center of mass of electrons from the relative motions of electrons for a parabolic band, we have derived and solved a Langevin-type equation for the fluctuating center-of-mass velocity operator \ensuremath{\delta}V^. The formulas for the current fluctuation spectrum ${\ensuremath{\Gamma}}_{\ensuremath{\Delta}I}$(\ensuremath{\omega}), the voltage fluctuation spectrum ${\ensuremath{\Gamma}}_{\ensuremath{\Delta}V}$(\ensuremath{\omega}), the diffusion coefficient ${D}_{s}$(t), and zero-frequency noise temperature ${T}_{n}$ have been derived microscopically. In particular, we obtain a generalized fluctuation-dissipation relation for the fluctuating force operator at a finite electric field and in nonequilibrium steady state. Analytical and numerical calculations of these quantities have been carried out for both degenerate and nondegenerate electron systems. While our results for a degenerate electron system may provide a better understanding of the quantum noise at extremely low lattice temperature, the essential features of our calculated diffusion coefficient and noise temperature for a nondegenerate electron system are in good agreement with those of Monte Carlo simulation.