Shot noises of spin and charge currents in a ferromagnet-quantum-dot-ferromagnet system

We have investigated the shot noises of charge and spin current by considering the spin polarized electron tunneling through a ferromagnet-quantum-dot-ferromagnet system. We have derived the spin polarized current noise matrix, from which we can derive general expressions of shot noises associated with charge and spin currents. The spin and charge currents are intimately related to the polarization angles, and they behave quite differently from each other. The shot noise of charge current is symmetric about the gate voltage whose structure is modified by the Zeeman field considerably. There exists oscillations in spin current shot noise in the absence of source-drain bias at zero temperature, and it is asymmetric in the positive and negative regimes of sourcedrain voltage. The shot noise of spin current behaves quite differently from the shot noise of charge current, since the spin current components I _x ^s , I _y ^s oscillate sinusoidally with the frequency ω_γ in the γth lead, while the I _z ^s component of spin current is independent of time.      

Modeling and simulations of the behavior of glass particles in a rotating drum in heptane and water vapor atmospheres

We have performed noise measurements on suspended ropes of single wall carbon nanotubes (SWNT) between 1 and 300 K for different values of dc current through the ropes. We find that the shot noise is suppressed by more than a factor 100 compared to the full shot noise 2eI. We have also measured an individual SWNT and found a level of noise which is smaller than the minimum expected. Another finding is the very low level of 1/f noise, which is significantly lower than previous observations. We propose two possible interpretations for the strong shot noise reduction: i) Transport within a rope takes place through few nearly ballistic tubes within a rope and possibly involves non integer effective charges with e ^*∼ 0.3e. ii) A substantial fraction of the tubes conduct with a strong reduction of effective charge (by more than a factor 50). Received 25 January 2002 Published online 19 July 2002     

Challenges in thermal noise for 3rd generation of gravitational wave detectors

Various noise sources limit the sensitivity of current interferometric gravitational wave detectors, including seismic noise, thermal noise of the optical components and suspension elements and photon shot noise. Plans are in place for a suite of hardware upgrades which should increase the sensitivity of these detectors by reducing the various noise sources. With these designs for 2nd generation detectors mature, techniques for further improvement of detector sensitivity by a factor of approximately 10 are under study. A particular challenge is the reduction of the thermal noise associated with the interferometer mirrors and their suspensions. We review the current status of research on thermal noise in interferometric gravitational wave detectors. Aspects of possible techniques for use in future ‘3rd generation detectors’ such as cryogenics and diffractive optics are discussed.     

A multi‐MHz single‐shot data acquisition scheme with high dynamic range: pump–probe X‐ray experiments at synchrotrons

The technical implementation of a multi‐MHz data acquisition scheme for laser–X‐ray pump–probe experiments with pulse limited temporal resolution (100 ps) is presented. Such techniques are very attractive to benefit from the high‐repetition rates of X‐ray pulses delivered from advanced synchrotron radiation sources. Exploiting a synchronized 3.9 MHz laser excitation source, experiments in 60‐bunch mode (7.8 MHz) at beamline P01 of the PETRA III storage ring are performed. Hereby molecular systems in liquid solutions are excited by the pulsed laser source and the total X‐ray fluorescence yield (TFY) from the sample is recorded using silicon avalanche photodiode detectors (APDs). The subsequent digitizer card samples the APD signal traces in 0.5 ns steps with 12‐bit resolution. These traces are then processed to deliver an integrated value for each recorded single X‐ray pulse intensity and sorted into bins according to whether the laser excited the sample or not. For each subgroup the recorded single‐shot values are averaged over ～10⁷ pulses to deliver a mean TFY value with its standard error for each data point, e.g. at a given X‐ray probe energy. The sensitivity reaches down to the shot‐noise limit, and signal‐to‐noise ratios approaching 1000 are achievable in only a few seconds collection time per data point. The dynamic range covers 100 photons pulse^?1 and is only technically limited by the utilized APD.     

Intracavity Multi-Photon-Absorption and the Quantum Noise Spectrum of Light

The intensity noise spectrum is investigated quantum-mechanically for incident coherent light passing through a resonator which is filled with a k-photon-absorber. For k? 2 the noise of the outgoing light is reduced below the shot noise level the reduction being maximal for frequencies that are small in comparison to the cavity bandwidth. It turns out that the highest possible value of this low-frequency noise reduction is obtained when the resonator losses due to transmission through the outcoupling mirror are 2k – 1 times as large as the k-photon absorption losses. In this case the noise at zero frequency is reduced with respect to the shot noise level by a factor of k/(2k – 1).     

Photoinduced current noise ina-Si: H solar cells

Summary Measurements of photoinduced current noise in amorphous silicon solar cells are reported. A 1/f ⁿ (n≈1) component, superimposed to a frequency-independent one due to simple shot noise, is attributed to the presence of defects limiting the conversion efficiency of the cell. In particular, large defects, such as local shorts or pin holes, can easily be detected since they are characterized by a very large increase of the 1/f ⁿ component. In general, even in the absence of such large defects, a correlation between the intensity of the 1/f ⁿ component and the cell conversion efficiency is found.     

Photon-assisted shot noise due to the charging effect in a quantum dot device

We have investigated the spectral density of shot noise for an ultra-small quantum dot(QD) system in the Coulomb blockade regime when irradiated with microwave fields (MWFs) by employing a nonequilibrium Green’s function technique. The shot noise is sensitive to Coulomb interaction, and the photon-assisted Coulomb blockade behaviour strongly modifies the mesoscopic transport. We have calculated the first and second derivatives of shot noise in the strong and weak coupling regimes to compare the theoretical results with existing experimental results. In the strong coupling regime, the first and second derivatives of shot noise display Fano type peak-valley structures around the charging channel 2E _c due to Coulomb interaction. When the magnitudes of the MWFs are sufficiently large, the system displays channel blockade due to photon irradiation. The photon-assisted and Coulomb blockade steps in the noise — as well as the resonant behaviour in the differential noise — are smeared by increasing temperature. The Coulomb interaction suppresses the shot noise, but the ac fields can either suppress the shot noise(balanced case) or enhance the shot noise(unbalanced case). The suppression of shot noise caused by ac fields in the balanced case is greater than that caused by Coulomb interaction in our system. Super-Poissonian shot noise may be induced due to the compound effects of strong Coulomb interaction and photon absorption-emission processes.     

High frequency noise of epitaxial graphene grown on sapphire

Microwave noise technique is applied to study in‐plane electronic properties of epitaxial graphene grown on sapphire by chemical vapor deposition and subjected to high electric field applied in the plane. The noise spectrum is measured in the field direction at room temperature. While a 1/f^1.25‐type dependence is observed in the 200 MHz–2.5 GHz band, a shot noise contribution is resolved at 10 GHz. The shot noise is possibly associated with hole jumps across the potential barriers located in the graphene layer. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

170 keV Proton radiation effects on low-frequency noise of bipolar junction transistors

In this paper, the electrical properties and low-frequency noise for bipolar junction transistors irradiated by 170?keV proton are examined. The result indicates that for the sample under proton irradiation with fluence 1.25?×?10^14?p/cm², base current I_B in low bias range (V_BE < 0.7?V) increases due to superimposition of radiation-induced recombination current, while the gain decreases significantly. Meanwhile, the low-frequency noise increases in the proton-irradiated sample. By analysis of evolution of parameters extracted from low-frequency noise power spectra, it is demonstrated that radiation-induced noise is mainly originated from carrier fluctuation modulated by generation–recombination centers (G–R centers) located at the interface of Si/SiO₂, which are introduced by proton-radiation-induced defects. It is also confirmed that the electrical properties and noise behavior of irradiated sample are mostly affected by the carrier recombination process caused by G–R centers at the interface of Si/SiO₂ than by G–R centers in EB junctions.     

Multi-photon behaviors of shot noise in a quantum dot system under the perturbation of two microwave fields

We have investigated the shot noise affected by the perturbation of two microwave fields (MWFs) with frequencies ω₁ and ω₂, which can be classified as the commensurate and incommensurate external ac fields. The time-dependent current correlation function and the spectral density of shot noise have been obtained. They are very different compared with the single-field applied system in the nonlinear regime of the ac potentials. The different photon absorption and emission processes induce different kinds of noise spectral density. We have performed the numerical calculations for both commensurate balanced and unbalanced photon absorptions and emissions. The multi-photon procedure can be seen clearly from the resonance of shot noise. Different commensurate number q = ω₂/ω₁ contributes to different photon absorption and emission behaviors. It is found that the asymmetric configuration of shot noise is intimately associated with the commensurate number q. The differential conductance appears symmetric and asymmetric behaviors, and the channel blockade exhibits. The shot noise is large enough to surpass its saturated value for the unbalanced photon absorption case. The sensitive behaviors of Fano factor associated with different commensurate numbers and amplitudes of ac fields signify that the shot noise can be controlled by external MWFs significantly.     

Design of the 10 m AEI prototype facility for interferometry studies

The AEI 10 m prototype interferometer facility is currently being constructed at the Albert Einstein Institute in Hannover, Germany. It aims to perform experiments for future gravitational wave detectors using advanced techniques. Seismically isolated benches are planned to be interferometrically interconnected and stabilized, forming a low-noise testbed inside a 100 m³ ultra-high vacuum system. A well-stabilized high-power laser will perform differential position readout of 100 g test masses in a 10 m suspended arm-cavity enhanced Michelson interferometer at the crossover of measurement (shot) noise and back-action (quantum radiation pressure) noise, the so-called Standard Quantum Limit (SQL). Such a sensitivity enables experiments in the highly topical field of macroscopic quantum mechanics. In this article we introduce the experimental facility and describe the methods employed; technical details of subsystems will be covered in future papers.     

A Direct Measurement Scheme of Two Quantum-Dot Qubits Quantum Correlation via Detector Current

By using the rate equation method we have investigated a scheme for measuring the quantum discord between two double quantum dot qubits via the current in quantum point-contact devices. The current of the detectors is same in-phase as the time-dependant of the quantum discord, and we can read out the most important time point when the quantum discord or quantum correlation reaches its maximum or minimum. Furthermore, in a special initial condition, the current can reflect the quantum discord. The shot noise of the detectors is calculated numerically. Which is dominated by the measured signal in single shot experiments.     

Extended wavelength InGaAs infrared (1.0–2.4 μm) detector arrays on SCIAMACHY for space-based spectrometry of the Earth atmosphere

Space qualified InGaAs solid-state array detectors, covering the near-infrared 1–2.4 μm wavelength range, have been developed for application in space-based spectroscopy of the Earth atmosphere. The SCIAMACHY atmospheric chemistry instrument on the ESA ENVISAT satellite (2002–2005) will be equipped with a series of these novel detectors. Detectors are arranged in linear arrays of 1024 pixels of 25×500 μm² dimension and meet requirements on modestly low operating temperature (150 K) and low levels of dark current and noise. In this paper the underlying physics of dark current and noise of the detector system is studied on the basis of a theoretical model in combination with measurements. At 2.4 μm wavelength the dark-current performance achieved is 20–100 fA at an operating temperature of 150 K and a bias voltage of −2 mV. This corresponds to a figure of merit for detector resistance R₀ times detector pixel area A of R₀A=2.5–12.5 MΩ cm². This result has required the development of a customised multiplexer for parallel detector read-out at near-zero bias voltage. Further reduction of the operating temperature will not result in lowering the dark current and noise of the InGaAs detectors which are shown to be limited by tunnelling current. A route to future improvement is discussed.     

碲镉汞焦平面光伏器件的实时γ辐照效应研究

对碲镉汞长波和中波焦平面光伏器件进行了实时γ射线辐照效应研究,通过辐照过程中实时测试器件的电流-电压特性,发现随着辐照剂量的增加,中波器件比长波器件表现出更好的抗辐照能力.对于长波器件,随着辐照剂量的增大,能够反映器件性能的零偏电阻逐渐降低;对于中波器件,零偏电阻随着辐照剂量的增加无固定变化趋势,辐照效应主要表现在电阻-电压曲线随着辐照剂量增加出现越来越明显的扰动.根据光伏器件的暗电流机理,对长波器件的电阻-电压曲线进行数值拟合,发现辐照引起少子产生-复合寿命逐渐降低,缺陷密度逐渐增大,主要影响的电流机理 关键词： γ辐照 辐照效应 光伏器件 碲镉汞     

Topological quantization of current in quantum tunnel contacts

It is shown that an account of the Berry phase (a topological ϑ-term), together with a dissipative term in the effective action S[ϕ] of the tunnel contacts, induces a strong quantization of the tunnel current at low temperatures. This phenomenon, as the Coulomb blockade, reflects a discrete charge structure of the quantum shot noise and can ensure a quantization of the tunnel current without a capacitive charging energy E _C when the latter is strongly suppressed by quantum fluctuations. Since the value of the ϑ parameter is determined by the gate voltage, this effect allows us to control the current through the contact. A possible physical application of this effect is proposed. The text was submitted by the author in English.     

Electron-electron scattering and nonequilibrium noise in sharvin contacts

We consider wide ballistic microcontacts with electron-electron scattering in the leads and calculate electric noise and nonlinear conductance in them. Due to a restricted geometry the collisions of electrons result in a shot noise even though they conserve the total momentum of electrons. We obtain the noise and the conductivity for arbitrary relations between voltage V and temperature T. The positive inelastic correction to the Sharvin conductance is proportional to T at low voltages eV ≪ T, and to |V| at high voltages. At low voltages the noise is defined by the Nyquist relation and at high voltages the noise is related with the inelastic correction to the current by the Schottky formula S _in = 2eI _in.     

Noise mechanisms investigation in pyroelectric infrared detectors based on Mn-doped Pb(Mg1/3Nb2/3)O3–0.27PbTiO3 vs. LiTaO3 single crystals

Different noise mechanisms between Mn-doped Pb(Mg_1/3Nb_2/3)O₃–0.27PbTiO₃ (Mn-PMNT) and LiTaO₃ (LT) based pyroelectric infrared detectors were observed under voltage mode, revealing that at low frequency of 10 Hz, dielectric loss noise dominates for Mn-PMNT based detectors, while resistance noise for LT based ones. Meanwhile, an extremely low equivalent voltage noise of appropriate 20 nV/Hz^1/2 was obtained in Mn-PMNT based detectors, 1/4 times lower than that of the LT based detectors. On the basis of the different noise mechanisms, frequency dependence of figure of merit for detectivity (F_d) have been deduced, providing significant reference values for the analysis of different materials based pyroelectric detectors.     

Some first passage time problems for shot noise processes

It has recently been shown that the first passage time problem for a certain class of one-dimensional processes that includes shot noise can be formulated in terms of a set of integral equations. These are found by exact enumeration of all possible trajectories. We show that the equations can be found by more direct means for processes described by the evolution equation , wheren(t) is time-localized shot noise.     

Coincidences among the data recorded by the baksan, kamioka and mont blanc underground neutrino detectors, and by the Maryland and Rome gravitational-wave detectors during Supernova 1987 A

Summary The data recorded with the neutrino detectors at Mont Blanc, Kamioka, Baksan and with the gravitational-wave detectors in Maryland and Rome have been analysed searching for correlations associated with SN 1987 A, without presuming or excluding hypotheses for correlations due to neutrinos and gravitational waves. The statistical analysis has been based on a previous analysis that showed a correlation among Maryland, Rome and Mont Blanc with a probability to be accidental less than 10⁻⁵. Independent correlations are found during a period of one or two hours, around the Mont Blanc 5ν burst (2h 52 min 36 s UT), among the various sets of data: Mont Blanc-Baksan with a probability to be accidental of the order ofp∼4·10⁻³, Mont Blanc-Kamioka withp∼4·10⁻³, Maryland-Rome-Kamioka withp∼5·10⁻⁴, Maryland-Rome-Baksan withp∼5·10⁻². It is remarkable that the events from all the neutrino detectors follow the signals from the g.w. detectors by a time of the order of 1/2 or 1 s. At present we will not give a physical interpretation of the observed correlations which have strong statistical significance. Professor Edoardo Amaldi died on December 5, 1989.     

Effect of different impurity atoms on 1/<Emphasis Type="Italic">f</Emphasis><Superscript>α</Superscript> tunneling current noise characteristics on InAs(110) surface

The results of UHV STM investigations of tunneling current noise spectra in the vicinity of individual impurity atoms on the InAs(110) surface are reported. It was found that the power law exponent of 1/f ^α noise depends on the presence of an impurity atom in the tunneling junction area. This is consistent with the proposed theoretical model considering tunneling current through a two-state impurity complex model system taking into account many-particle interaction. The text was submitted by the authors in English.