Shot noise measurements are widely used for the characterization of nonequilibrium configurations in electronic conductors. The recently introduced quantum tomography approach was implemented for the studies of electronic wavefunctions of few-electron excitations created by periodic voltage pulses in phase-coherent ballistic conductors based on the high-quality GaAs two-dimensional electron gas. Still relying on the manifestation of Fermi correlations in noise, we focus on the simpler and more general approach beneficial for the local measurements of energy distribution (ED) in electronic systems with arbitrary excitations with well-defined energies and random phases. Using biased diffusive metallic wire as a testbed, we demonstrate the power of this approach and extract the well-known double-step ED from the shot noise of a weakly coupled tunnel junction. Our experiment paves the way for the local measurements of generic nonequilibrium configurations applicable to virtually any conductor.
We present a general analysis of shot noise in an electronic Mach-Zehnder interferometer, of the type investigated experimentally [Yang Ji et al., Nature 422, 415 (2003)], under the influence of dephasing produced by fluctuations of a classical field. We show how the usual partition noise expression T(1-T) is modified by dephasing, depending on the power spectrum of the environmental fluctuations.
We investigate the charge and heat electronic noise in a generic two-terminal mesoscopic conductor in the absence of the corresponding charge and heat currents. Despite these currents being zero, shot noise is generated in the system. We show that, irrespective of the conductor's details and the specific nonequilibrium conditions, the charge shot noise never exceeds its thermal counterpart, thus establishing a general bound. Such a bound does not exist in the case of heat noise, which reveals a fundamental difference between charge and heat transport under zero-current conditions.
Fluctuations pose fundamental limitations in making sensitive measurements, yet at the same time, noise unravels properties that are inaccessible at the level of the averaged signal. In electronic devices, shot noise arises from the discrete nature of charge carriers and it increases linearly with the applied voltage according to the celebrated Schottky formula. Nonetheless, measurements of shot noise in atomic-scale junctions at high voltage reveal significant nonlinear (anomalous) behavior, which varies from sample to sample, and has no specific trend. Here, we provide a viable, unifying exp…
The shot noise in the electrical current through a ballistic chaotic quantum dot with N-channel point contacts is suppressed for N --> infinity, because of the transition from stochastic scattering of quantum wave packets to deterministic dynamics of classical trajectories. The dynamics of the electron spin remains quantum mechanical in this transition, and can affect the electrical current via spin-orbit interaction. We explain how the role of the channel number N in determining the shot noise is taken over by the ratio l_{so}/lambda_F of spin precession length l_{so} and Fermi wave length la…
We present a theoretical study of the influence of dephasing on shot noise in an electronic Mach-Zehnder interferometer. In contrast to phenomenological approaches, we employ a microscopic model where dephasing is induced by the fluctuations of a classical potential. This enables us to treat the influence of the environment's fluctuation spectrum on the shot noise. We compare against the results obtained from a simple classical model of incoherent transport, as well as those derived from the phenomenological dephasing terminal approach, arguing that the latter runs into a problem when applied …
We study the behavior of shot noise in resonant tunneling junctions far from equilibrium. Quantum-coherent elastic charge transport can be characterized by a transmission function, that is the probability for an incoming electron at a given energy to tunnel through a potential barrier. In systems such as quantum point contacts, electronic shot noise is oftentimes calculated based on a constant (energy independent) transmission probability, a good approximation at low temperatures and under a small bias voltage. Here, we generalize these investigations to far from equilibrium settings by evalua…
By solving a master equation in the Sierpinski lattice and in a planar random-resistor network, we determine the scaling with size L of the shot noise power P due to elastic scattering in a fractal conductor. We find a power-law scaling P ~ L^(d_f-2-alpha), with an exponent depending on the fractal dimension d_f and the anomalous diffusion exponent alpha. This is the same scaling as the time-averaged current I, which implies that the Fano factor F=P/2eI is scale independent. We obtain a value F=1/3 for anomalous diffusion that is the same as for normal diffusion, even if there is no smallest l…
We report on direct measurements of the electronic shot noise of a quantum point contact at frequencies nu in the range 4-8 GHz. The very small energy scale used ensures energy independent transmissions of the few transmitted electronic modes and their accurate knowledge. Both the thermal energy and the quantum point contact drain-source voltage Vds are comparable to the photon energy hnu leading to observation of the shot noise suppression when $V_{ds}<hν/e$. Our measurements provide the first complete test of the finite frequency shot noise scattering theory without adjustable parameters.
A theory is presented for the photodetection statistics of radiation produced by current fluctuations in a phase-coherent conductor. Deviations are found from the Poisson statistics that would result from a classical current. For detection in a narrow frequency interval, the photocount distribution has the negative-binomial form of black-body radiation if this frequency interval is less than the mean current in the conductor. When electronic localization sets in, a different type of super-Poissonian photon statistics results.
When assembling individual quantum components into a mesoscopic circuit, the interplay between Coulomb interaction and charge granularity breaks down the classical laws of electrical impedance composition. Here we explore experimentally the thermal consequences, and observe an additional quantum mechanism of electronic heat transport. The investigated, broadly tunable test-bed circuit is composed of a micron-scale metallic node connected to one electronic channel and a resistance. Heating up the node with Joule dissipation, we separately determine, from complementary noise measurements, both i…
Quantum electronic noise, the random current fluctuations generated by electrons crossing a quantum conductor, has been thoroughly studied from the electron point of view. Recent experiments have shown that such noise may have striking properties in terms of the quantum electromagnetic field it generates. Both the existence of vacuum squeezing \cite{PAN_squeezing} and generation of correlated photon pairs \cite{C4quantique} have been observed. Here we demonstrate that this electromagnetic field also violates Bell-like inequalities, thereby proving its true quantum nature. This is achieved by t…
A non-perturbative treatment is developed for the dephasing produced by the shot noise of a one- dimensional electron channel. It is applied to two systems: a charge qubit and the electronic Mach-Zehnder interferometer, both of them interacting with an adjacent partitioned electronic channel acting as a detector. We find that the visibility (interference contrast) can display oscillations as a function of detector voltage and interaction time. This is a unique consequence of the non-Gaussian properties of the shot noise, and only occurs in the strong coupling regime, when the phase contributed…
The noise power spectral density of a thermal current between two macroscopic dielectric bodies held at different temperatures and connected only at a quantum point contact is calculated. Assuming the thermal energy is carried only by phonons, we model the quantum point contact as a mechanical link, having a harmonic spring potential. In the weak coupling, or weak-link limit, we find the thermal current analog of the well-known electronic shot-noise expression.
The shot noise in the current through a quantum dot is calculated as a function of voltage from the high-voltage, Coulomb blockaded regime to the low-voltage, Kondo regime. Using several complementary approaches, it is shown that the zero-frequency shot noise (scaled by the voltage) exhibits a non-monotonic dependence on voltage, with a peak around the Kondo temperature. Beyond giving a good estimate of the Kondo temperature, it is shown that the shot noise yields additional information on the effects of electronic correlations on the local density of states in the Kondo regime, unaccessible i…
We study the full counting statistics (FCS) in a single-molecule magnet (SMM) with finite Coulomb interaction $U$. For finite $U$ the FCS, differing from $U\rightarrow \infty $, shows a symmetric gate-voltage-dependence when the coupling strengths with two electrodes are interchanged, which can be observed experimentally just by reversing the bias-voltages. Moreover, we find that the effect of finite $U$ on shot noise depends on the internal level structure of the SMM and the coupling asymmetry of the SMM with two electrodes as well. When the coupling of the SMM with the incident-electrode is …
The orbital angular momentum L as an integer can be ultimately factorized as a product of prime numbers. We show here a close relation between the resolution of L and the classification of quantum states of an N-electron 2-dimensional system. In this scheme, the states are in essence classified into different types according to the m(k)-accessibility, namely the ability to get access to symmetric geometric configurations. The m(k)-accessibility is an universal concept underlying all kinds of 2-dimensional systems with a center. Numerical calculations have been performed to reveal the electroni…
In a recent letter (Phys.Rev.Lett. 82, 1526 (1999)), van den Brom and van Ruitenbeek found a pronounced suppression of the shot noise in atom-size gold contacts with conductances near integer multiples of $G_0=2e^2/h$, revealing unambiguously the quantized nature of the electronic transport. However, the ad hoc model they introduced to describe the contribution of partially-open conductance channels to the shot noise is unable to fit either the maxima or minima of their shot noise data. Here we point out that a model of quantum-confined electrons with disorder quantitatively reproduces their m…
We investigate the zero-frequency shot noise of electronic tunneling through a single quantum dot (SQD) and coherently coupled quantum dots (CQD) taking into account the Coulomb interaction. Within Hartree-Fock approximation, the analytical expressions of current and zero-frequency shot noise are self-consistently derived in the framework of full counting statistics for the both systems. We demonstrate that the correction term of zero-frequency shot noise induced by the intradot Coulomb interaction is almost negligible compared to the noninteracting shot noise in a SQD, while in a CQD the inte…
When subjected to electromagnetic radiation, the fluctuation of the electronic current across a quantum conductor increases. This additional noise, called photon-assisted shot noise, arises from the generation and subsequent partition of electron-hole pairs in the conductor. The physics of photon-assisted shot noise has been thoroughly investigated at microwave frequencies up to 20 GHz, and its robustness suggests that it could be extended to the Terahertz (THz) range. Here, we present measurements of the quantum shot noise generated in a graphene nanoribbon subjected to a THz radiation. Our r…
A theoretical non-pertubative treatment is developed to explain the dephasing of electrons in the electronic Mach-Zehnder interferometer via interaction with a near-by partitioned electronic channel, which acts as a "which path" detector. The resulting formula reproduces the recant experimental behavior of the MZI interference visibility. By fitting the model to the experimental results, it is shown that the visibility is strongly influenced by merely ~3 detecting electrons, hence it reflects the Non-Gaussian properties behavior of the detector shot-noise.
ReSe2 and ReS2 are unusual compounds amongst the layered transition metal dichalcogenides as a result of their low symmetry, with a characteristic in-plane anisotropy due to in-plane rhenium chains. They preserve inversion symmetry independent of the number of layers and, in contrast to more well-known transition metal dichalcogenides, bulk and few-monolayer Re-TMD compounds have been proposed to behave as electronically and vibrational decoupled layers. Here, we probe for the first time the electronic band structure of bulk ReSe2 by direct nanoscale angle-resolved photoemission spectroscopy. …
We performed the conductance and the shot noise measurements in an electronic Mach-Zehnder interferometer. The visibility of the interference is investigated as a function of the electron temperature that is derived from the thermal noise of the interferometer. The non-equilibrium noise displays both h/e and h/2e oscillations vs. the modulation gate voltage.
The electronic structure of molecules on metal surfaces is largely determined by hybridization and screening by the substrate electrons. As a result, the energy levels are significantly broadened and molecular properties, such as vibrations are hidden within the spectral lineshapes. Insertion of thin decoupling layers reduces the linewidths and may give access to the resolution of electronic and vibronic states of an almost isolated molecule. Here, we use scanning tunneling microscopy and spectroscopy to show that a single layer of MoS$_{2}$ on Ag(111) provides a semiconducting band gap that m…
New experiments that measure the low-frequency shot-noise spectrum at local tunneling contacts on mesoscopic structures are proposed. The current fluctuation spectrum at a single tunneling tip is determined by local partial densities of states. The current-correlation spectrum between two tunneling tips is sensitive to non-diagonal density of states elements which are expressed in terms of products of scattering states of the conductor. Thus such an experiment permits to investigate correlations of electronic wave functions. We present specific results for a clean wire with a single barrier an…
We study nonequilibrium dephasing in an electronic Mach-Zehnder interferometer. We demonstrate that the shot noise at the beam splitter of the interferometer generates an ensemble of nonequilibrium electron density configurations and that electron interactions induce configuration-specific phase shifts of an interfering electron. The resulting dephasing exhibits two characteristic features, a lobe pattern in the visibility and phase jumps of $π$, in good agreement with experimental data.
Random fluctuations of the shot-noise power in disordered graphene nanoribbons are studied. In particular, we calculate the distribution of the shot noise of nanoribbons with zigzag and armchair edge terminations. We show that the shot noise statistics is different for each type of these two graphene structures, which is a consequence of presence of different electron localizations: while in zigzag nanoribbons electronic edge states are Anderson localized, in armchair nanoribbons edge states are absent, but electrons are anomalously localized. Our analytical results are verified by tight bindi…
Determination of qubit initialisation and measurement fidelity is important for the overall performance of a quantum computer. However, the method by which it is calculated in semiconductor qubits varies between experiments. In this paper we present a full theoretical analysis of electronic single-shot readout and describe critical parameters to achieve high fidelity readout. In particular, we derive a model for energy selective state readout based on a charge detector response and examine how to optimise the fidelity by choosing correct experimental parameters. Although we focus on single ele…
We report on shot noise measurements in carbon nanotube based Fabry-Perot electronic interferometers. As a consequence of quantum interferences, the noise power spectral density oscillates as a function of the voltage applied to the gate electrode. The quantum shot noise theory accounts for the data quantitatively. It allows to confirm the existence of two nearly degenerate orbitals. At resonance, the transmission of the nanotube approaches unity, and the nanotube becomes noiseless, as observed in quantum point contacts. In this weak backscattering regime, the dependence of the noise on the ba…
The recent realization of coherent single-electron sources in ballistic conductors let us envision performing time-resolved electronic interferometry experiments analogous to quantum optics experiments.One could eventually use propagating electronic excitations as flying qubits. However an important missing brick is the single-shot electron detection which would enable a complete quantum information operation with flying qubits. Here, we propose and discuss the design of a single charge detector able to achieve in-flight detection of electron flying qubits. Its sub-electron sensitivity would a…
A recent theory is reviewed for the shot noise of coherent radiation propagating through a random medium. The Fano factor P/I (the ratio of the noise power and the mean transmitted current) is related to the scattering matrix of the medium. This is the optical analogue of Buttiker's formula for electronic shot noise. Scattering by itself has no effect on the Fano factor, which remains equal to 1 (as for a Poisson process). Absorption and amplification both increase the Fano factor above the Poisson value. For strong absorption P/I has the universal limit 1+3f/2 with f the Bose-Einstein functio…
We report on a direct experimental evidence of shot noise in a linear macroscopic resistor. The origin of the shot noise comes from the fluctuation of the total number of charge carriers inside the resistor associated with their diffusive motion under the condition that the dielectric relaxation time becomes longer than the dynamic transit time. Present results show that neither potential barriers nor the absence of inelastic scattering are necessary to observe shot noise in electronic devices.
We report a method for fabricating nanogaps directly with electron beam lithography (EBL). The primary resolution-limit of EBL, electron back-scattering, is reduced dramatically by using a thin-film as a substrate. We show that this resolution enhancement allows one to fabricate metal electrodes with separation from arbitrarily large to under one nanometer. Furthermore, because these nanogaps are on a thin film, they can be imaged with high-resolution transmission electron microscopy (HRTEM). Using these nanogaps we measured the charge transport through several coupled PbSe nanocrystals and co…
Electronic properties of mesoscopic systems made of normal metal in contact with normal and superconducting reservoirs are determined by Andreev Reflection. We address both experimentally and theoretically how Andreev Reflection manifests itself in shot noise experiments and what physics can be deduced from such measurements. We report high frequency measurements in which Andreev Reflection affects the distribution statistics of the electronic excitations, resulting in a shift of the classical-to-quantum regime or equilibrium-to-shot noise crossovers. We also demonstrate that the effective cha…
Owing to a linear and gapless band structure and a tunability of the charge carrier type, graphene offers a unique system to investigate transport of Dirac Fermions at p-n junctions (PNJs). In a magnetic field, combination of quantum Hall physics and the characteristic transport across PNJs leads to a fractionally quantized conductance associated with the mixing of electron-like and hole-like modes and their subsequent partitioning. The mixing and partitioning suggest that a PNJ could be used as an electronic beam-splitter. Here we report the shot noise study of the mode mixing process and dem…
We investigate the behavior of the shot-noise power through quantum mechanical cavities in the semiclassical limit of small electronic wavelength. In the absence of impurity scattering, the Fano factor $F$, giving the noise to current ratio, was previously found to disappear as more and more classical, hence deterministic and noiseless transmission channels open up. We investigate the behavior of $F$ as diffractive impurities are added inside the cavity. We find that $F$ recovers its universal value provided (i) impurities cover the full cavity so that only a set of zero measure of classical t…
Optically-detected magnetic resonance using Nitrogen Vacancy (NV) color centres in diamond is a leading modality for nanoscale magnetic field imaging, as it provides single electron spin sensitivity, three-dimensional resolution better than 1 nm, and applicability to a wide range of physical and biological samples under ambient conditions. To date, however, NV-diamond magnetic imaging has been performed using real space techniques, which are either limited by optical diffraction to 250 nm resolution or require slow, point-by-point scanning for nanoscale resolution, e.g., using an atomic force …
We investigate the electronic transport through a single molecule in a strong electron-phonon coupling regime. Based on a particle-hole transformation which is made suitable for non-equilibrium situation, we treat the pair tunneling and cotunneling on an equal footing. We propose an experimental setup to enhance the visibility of pair tunneling, which has no Franck-Condon suppression. We also discuss the shot noise characteristics.
We have studied electronic conductivity and shot noise of bilayer graphene (BLG) sheets at high bias voltages and low bath temperature $T_0=4.2$ K. As a function of bias, we find initially an increase of the differential conductivity, which we attribute to self-heating. At higher bias, the conductivity saturates and even decreases due to backscattering from optical phonons. The electron-phonon interactions are also responsible for the decay of the Fano factor at bias voltages $V>0.1$ V. The high bias electronic temperature has been calculated from shot noise measurements, and it goes up to $\s…
We show how shot noise in an electronic Mach-Zehnder interferometer in the fractional quantum Hall regime probes the charge and statistics of quantum Hall quasiparticles. The dependence of the noise on the magnetic flux through the interferometer allows for a simple way to distinguish Abelian from non-Abelian quasiparticle statistics. In the Abelian case, the Fano factor (in units of the electron charge) is always lower than unity. In the non-Abelian case, the maximal Fano factor as a function of the magnetic flux exceeds one.
We present the first measurements of the third moment of the voltage fluctuations in a conductor. This technique can provide new and complementary information on the electronic transport in conducting systems. The measurement was performed on non-superconducting tunnel junctions as a function of voltage bias, for various temperatures and bandwidths up to 1GHz. The data demonstrate the significant effect of the electromagnetic environment of the sample.
We study a model of two interacting levels that are attached to two electronic leads, where one of the levels is attached very weakly to the leads. We use rate equations method to calculate the average current and the noise of electrons transmitted through the two levels. We show that the shot noise is enhanced due to the interactions and that the Fano factor depends on the properties of the couplings between the levels and the leads. We study both sequential tunneling and cotunneling processes and show that there is a range of parameters in which the cotunneling processes affect the noise sig…
We analyze the shot noise in a voltage biased superconducting quantum point-contact. Results are presented for the single channel case with arbitrary transmission. In the limit of very low transmission it is found that the effective charge, defined from the noise-current ratio, exhibits a step-like behavior as a function of voltage with well defined plateaus at integer values of the electronic charge. This multiple charge corresponds to the transmitted charge in a Multiple Andreev Reflection (MAR) process. This effect gradually disappears for increasing transmission due to interference between…
