Abstract:
We discuss how threshold detectors can be used for a direct measurement of the full counting statistics (FCS) of current fluctuations and how to implement Jose phson junctions in this respect. We propose a scheme to characterize the full co unting statistics from the current dependence of the escape rate measured. We il lustrate the scheme with explicit results for tunnel, diffusive and quasi-ballis tic mesoscopic conductors.

Abstract:
We present a theory for the full distribution of current fluctuations in incoherent diffusive superconducting junctions, subjected to a voltage bias. This theory of full counting statistics of incoherent multiple Andreev reflections is valid for arbitrary applied voltage. We present a detailed discussion of the properties of the first four cumulants as well as the low and high voltage regimes of the full counting statistics. The work is an extension of the results of Pilgram and the author, Phys. Rev. Lett. 94, 086806 (2005).

Abstract:
We present an investigation of the energy dependence of the full charge counting statistics in diffusive normal-insulating-normal-insulating-superconducting junctions. It is found that the current in general is transported via a correlated transfer of pairs of electrons. Only in the case of strongly asymmetric tunnel barriers or energies much larger than the Thouless energy is the pair transfer uncorrelated. The second cumulant, the noise, is found to depend strongly on the applied voltage and temperature. For a junction resistance dominated by the tunnel barrier to the normal reservoir, the differential shot noise shows a double peak feature at voltages of the order of the Thouless energy, a signature of an ensemble averaged electron-hole resonance.

Abstract:
We present a formalism to calculate finite-frequency current correlations in interacting nanoscale conductors. We work within the n-resolved density matrix approach and obtain a multi-time cumulant generating function that provides the fluctuation statistics, solely from the spectral decomposition of the Liouvillian. We apply the method to the frequency-dependent third cumulant of the current through a single resonant level and through a double quantum dot. Our results, which show that deviations from Poissonian behaviour strongly depend on frequency, demonstrate the importance of finite-frequency higher-order cumulants in fully characterizing interactions.

Abstract:
The full counting statistics of a molecular level weakly interacting with a local phonon mode is derived. We find an analytic formula that gives the behavior of arbitrary irreducible moments of the distribution upon phonon excitation. The underlying competition between quasi-elastic and inelastic processes results in the formation of domains in parameter space characterized by a given sign in the jump of the irreducible moments. In the limit of perfect transmission, the corresponding distribution is distorted from Gaussian statistics for electrons to Poissonian transfer of holes above the inelastic threshold.

Abstract:
We demonstrate that the probability distribution of the net number of electrons passing through a quantum system in a junction obeys a steady-state fluctuation theorem (FT) which can be tested experimentally by the full counting statistics (FCS) of electrons crossing the lead-system interface. The FCS is calculated using a many-body quantum master equation (QME) combined with a Liouville space generating function (GF) formalism. For a model of two coupled quantum dots, we show that the FT becomes valid for long binning times and provide an estimate for the finite-time deviations. We also demonstrate that the Mandel (or Fano) parameter associated with the incoming or outgoing electron transfers show subpoissonian (antibunching) statistics.

Abstract:
We study the full-counting statistics of charges transmitted through a single-level quantum dot weakly coupled to a local Einstein phonon which causes fluctuations in the dot energy. An analytic expression for the cumulant generating function, accurate up to second order in the electron-phonon coupling and valid for finite voltages and temperatures, is obtained in the extended wide-band limit. The result accounts for nonequilibrium phonon distributions induced by the source-drain bias voltage, and concomitantly satisfies the fluctuation theorem. Extending the counting field to the complex plane, we investigate the locations of possible singularities of the cumulant generating function, and exploit them to identify regimes in which the electron transfer is affected differently by the coupling to the phonons. Within a large-deviation analysis, we find a kink in the probability distribution, analogous to a first-order phase transition in thermodynamics, which would be a unique hallmark of the electron-phonon correlations. This kink reflects the fact that although inelastic scattering by the phonons once the voltage exceeds their frequency can scatter electrons opposite to the bias, this will never generate current flowing against the bias at zero temperature, in accordance with the fluctuation theorem.

Abstract:
I study the dynamics of a Josephson junction serving as a threshold detector of fluctuations which is subjected to a general non-equilibrium electronic noise source whose characteristics is to be determined by the junction. This experimental setup has been proposed several years ago as a prospective scheme for determining the Full Counting Statistics of the electronic noise source. Despite of intensive theoretical as well as experimental research in this direction the promise has not been quite fulfilled yet and I will discuss what are the unsolved issues. First, I review a general theory for the calculation of the exponential part of the non-equilibrium switching rates of the junction and compare its predictions with previous results found in different limiting cases by several authors. I identify several possible weak points in the previous studies and I report a new analytical result for the linear correction to the rate due to the third cumulant of a non-Gaussian noise source in the limit of a very weak junction damping. The various analytical predictions are then compared with the results of the developed numerical method. Finally, I analyze the status of the so-far publicly available experimental data with respect to the theoretical predictions and discuss briefly the suitability of the present experimental schemes in view of their potential to measure the whole FCS of non-Gaussian noise sources as well as their relation to the available theories.

Abstract:
We study the statistics of heat transferred in a given time interval $t_M$, through a finite harmonic chain, called the center $(C)$, which is connected with two heat baths, the left $(L)$ and the right $(R)$, that are maintained at two different temperatures. The center atoms are driven by an external time-dependent force. We calculate the cumulant generating function (CGF) for the heat transferred out of the left lead, $Q_L$, based on two-time measurement concept and using nonequilibrium Green's function (NEGF) method. The CGF can be concisely expressed in terms of Green's functions of the center and an argument-shifted self-energy of the lead. The expression of CGF is valid in both transient and steady state regimes. We consider three different initial conditions for the density operator and show numerically, for one-dimensional (1D) linear chains, how transient behavior differs from each other but finally approaches the same steady state, independent of the initial distributions. We also derive the CGF for the joint probability distribution $P(Q_L,Q_R)$, and discuss the correlations between $Q_L$ and $Q_R$. We calculate the total entropy flow to the reservoirs. In the steady state we explicitly show that the CGF obeys steady state fluctuation theorem (SSFT). Classical results are obtained by taking $\hbar \to 0$. The method is also applied to the counting of the electron number and electron energy, for which the associated self-energy is obtained from the usual lead self-energy by multiplying a phase or shifting the contour time, respectively.

Abstract:
We study current-induced vibrational cooling, heating, and instability in a donor-acceptor rectifying molecular junction using a full counting statistics approach. In our model, electron-hole pair excitations are coupled to a given molecular vibrational mode which is either harmonic or highly anharmonic. This mode may be further coupled to a dissipative thermal environment. Adopting a master equation approach, we confirm the charge and heat exchange fluctuation theorem in the steady-state limit, for both harmonic and anharmonic models. Using simple analytical expressions, we calculate the charge current and several measures for the mode effective temperature. At low bias, we observe the effect of bias-induced cooling of the vibrational mode. At higher bias, the mode effective temperature is higher than the environmental temperature, yet the junction is stable. Beyond that, once the vibrational mode (bias-induced) excitation rate overcomes its relaxation rate, instability occurs. We identify regimes of instability as a function of voltage bias and coupling to an additional phononic thermal bath. Interestingly, we observe a reentrant behavior where an unstable junction can properly behave at a high enough bias. The mechanism for this behavior is discussed.