Full counting statistics ͑FCS͒ of charge transfer in mesoscopic systems has recently become a subject of significant interest, since it proves to reveal an important information about the system which can be hardly assessed by other means. While the previous research mostly addressed the FCS of noninteracting systems, the present paper deals with the FCS in the limit of strong interaction. In this Coulomb blockade limit the electron dynamics is known to be governed by a master equation. We develop a general scheme to evaluate the FCS in such case, this being the main result of the work presented. We illustrate the scheme, by applying it to concrete systems. For generic case of a single resonant level we establish the equivalence of scattering and master equation approach to FCS. Further we study a single Coulomb blockade island with two and three leads attached and compare the FCS in this case with our recent results concerning an open dot either with two and three terminals. We demonstrate that Coulomb interaction suppresses the relative probabilities of large current fluctuations.

In a variety of mesoscopic systems shot noise is seen to be suppressed in comparison with its Poisson value. In this work we observe a considerable enhancement of shot noise in the case of resonant tunneling via localized states. We present a model of correlated transport through two localized states which provides both a qualitative and a quantitative description of this effect.

We propose a theory that treats the current, noise, and, generally, the full current statistics of electron transfer in a mesoscopic system in a unified, simple, and efficient way. The theory appears to be a circuit theory of 2 3 2 matrices associated with Keldysh Green functions. We illustrate the theory by considering the big fluctuations of currents in various three-terminal circuits. DOI: 10.1103/PhysRevLett.88.196801 PACS numbers: 73.23. -b, 05.40. -a, 72.70. +m, 74.40. +k The field of quantum noise in mesoscopic systems has exploded during the last decade, with most achievements being summarized in a recent review article [1]. Measurement of fractional charge in quantum Hall regime [2], noise measurements in atomic-size junctions [3], and superconductors [4] are milestones of the field and demonstrate the importance of quantum noise as a unique tool to study electron correlations and entanglements of different kinds. A very important step has been made in [5] where an elegant theory of full counting statistics (FCS) has been presented. This theory encompasses not only noise, but all higher momenta of the charge transfer.Starting from the pioneering work of Büttiker [6], special attention has been paid to noise and statistics of electron transfer in multiterminal circuits. The correlations of currents flowing to different terminals reveal Fermi statistics of electrons. These cross correlations have been recently observed [7]. Although the noise correlations for several relevant layouts have been understood [1], the evaluation of FCS still encountered difficulties. For instance, an attempt to build up FCS with the "minimal correlation approach" [8] has led to contradictions [9]. This is unfortunate, since higher-order current correlations supply information about higher-order electron correlations and multiparticle interference. This information is of fundamental importance and can be hardly obtained by any other means.In this Letter, we present a calculation scheme that allows for easy evaluation of FCS in a multiterminal mesoscopic system. It is of great intellectual enjoyment that this scheme is a simple and a universal one. In fact, it is hardly more complicated than a conventional circuit theory of electric transport and is based on a slight extension of Kirchoff rules to 2 3 2 matrix structures.We start by introducing current operatorsÎ i , each being associated with the current to a certain terminal i. Extending the method of [10] we introduce a Keldysh-type Green function defined by √Here we follow notations of a comprehensive review [11], x i are time-dependent parameters,t 3 is a 2 3 2 matrix in Keldysh space, andĤ is the one-particle Hamiltonian that incorporates all information about the system layout, including boundaries, defects, and all kinds of elastic scattering. We use "hat," "bar," and "check" to denote operators in coordinate space, matrices in Keldysh space, and operators in direct product of these spaces, respectively. Equation (1) One can easily see by traditional diagrammatic me...

In order to fully characterize the noise associated with electron transport, with its severe consequences for solid-state quantum information systems, the theory of full counting statistics has been developed. It accounts for correlation effects associated with the statistics and effects of entanglement, but it remains a non-trivial task to account for interaction effects. In this article we present two examples: we describe electron transport through quantum dots with strong charging effects beyond perturbation theory in the tunneling, and we analyze current fluctuations in a diffusive interacting conductor.Recently further links became apparent between the FCS of electron transport and the field of solid-state quantum information processing. One of these is related to the use of electron entangled states for these purposes. Most of the work on entanglement has been performed in optical systems with photons [13], cavity QED systems [14] and ion traps [15]. By now several ideas have been put forward how to generate, manipulate and detect electronic entangled states [16]. It turns out that in solid state systems entanglement is rather common, the nontrivial task remaining its control and detection. For mesoscopic conductors, the prototype scheme of such detection was discussed in [17]. It has been shown that the presence of spatially separated pairs of entangled electrons, created by some entangler, can be revealed by using a beam splitter and by measuring the correlations of the current fluctuations in the leads. If the electrons are injected in an entangled state, bunching and anti-bunching of the cross-correlations of current fluctuations should be found, depending on whether the state is a spin singlet or triplet. In [18] the FCS of entangled electrons has been analyzed in detail. The FCS depends not only on the scattering properties of the conductor but also on the correlations among the electrons that compose the incident beam. In [19] the Clauser-Horne inequality test for the FCS in the multi-terminal structures has been proposed in order to detect the entanglement in the source flux of electrons.A second link is the intrinsic relation between FCS and detector properties of a quantum point contact. QPCs were suggested as charge detectors in [20] and have been studied experimentally in [21]. Recently they have been used as detectors for the state of quantum-dot qubits [22][23][24]. The operating principle of the QPC detector relies on the dependence of the electron current I through the QPC on the state of the two-level system. In [25] the detector properties of the QPC have been calculated beyond linear-response for arbitrary energy-dependent transparency and coupling. This is the case of interest since for maximum detector sensitivity typical measurements are done in the regime of high QPC transparency, D 1/2, and for coupling that is not weak [22]. It was found that both the back-action dephasing rate Γ and the measurement rate W are determined by the electron FCS.

The tunnel magnetoresistance ͑TMR͒ of F/O/F magnetic junctions (F's are ferromagnetic layers and O is an oxide spacer͒ in the presence of magnetic impurities within the barrier, is investigated. We assume that magnetic couplings exist both between the spin of the impurity and the bulk magnetization of the neighboring magnetic electrode, and between the spin of the impurity and the spin of the tunneling electron. Consequently, the resonant levels of the system formed by a tunneling electron and a paramagnetic impurity with spin S ϭ1 are a sextet, and the resonant tunneling depends on the direction of the tunneling electron spin. At low temperatures and zero bias voltage, the TMR of the considered system may be larger than that of the same structure without paramagnetic impurities. It is calculated that an increase in temperature leads to a decrease in the TMR amplitude due to excitation of spin-flip processes resulting in mixing of spin-up and down channels. It is also shown that asymmetry in the location of the impurities within the barrier can lead to asymmetry in I(V) characteristic of impurity-assisted current. Two mechanisms responsible for the origin of this effect are identified. The first one is due to the excitation of spin-flip processes at low voltages and the second one arises from the shift of resonant levels inside the insulator layer under high applied voltages.