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The theory of full counting statistics allows complete characterization of charge transport processes through nanoscale systems. The majority of existing theoretical treatments used to obtain the current cumulants rely on perturbative approximations with respect to either the system-bath coupling or the electronic tunnelling coupling within the system. This is not generally well suited to electron transfer through organic molecules where these couplings can be on the same order of magnitude. Here we present a non-perturbative approach that uses the formalism of the hierarchical equations of motion to describe the system-bath dynamics while retaining a weak coupling with respect to source and drain leads. The scope of this new framework is demonstrated by comparisons with a perturbative approach for a dimer system coupled to a thermal bath. The inadequacy of the perturbative approach to describe current fluctuations in a variety of regimes is shown.

In their Letter [Phys. Rev. Lett. 105, 137402 (2010)], Eisfeld et al. predicted the exchange broadening and blue-shift of the absorption band as well as a nonuniversal disorder scaling of the localization length of excitons in J-aggregates with Levy disorder, which they contrasted with the previously analyzed Gaussian and Lorentzian case [Phys. Rev. B, 79, 1 (2009)]. The observations were explained by chain segmentation due to outliers, and its interplay with localization of states in effective potential wells created by typical random site energies. We argue that the previously known theory does not break down and thus anticipates the properties of absorption band investigated in the commented work., Comment: Phys. Rev. Lett. 109, 259701 (2012) (subm on 29 Nov 2011)

We derive a many-site version of the non-Markovian time-convolutionless polaron master equation [S. Jang et al., J. Chem Phys. 129, 101104 (2008)] to describe electronic excitation dynamics in multichromophoric systems. By treating electronic and vibrational degrees of freedom in a combined frame (polaron frame), this theory is capable of interpolating between weak and strong exciton-phonon coupling and is able to account for initial non-equilibrium bath states and spatially correlated environments. Besides outlining a general expression for the expected value of any electronic system observable in the original frame, we also discuss implications of the Markovian and secular approximations highlighting that they need not hold in the untransformed frame despite being strictly satisfied in the polaron frame. The key features of the theory are illustrated using as an example a four-site subsystem of the Fenna-Mathew-Olson light-harvesting complex. For a spectral density including a localised high-energy mode, we show that oscillations of site populations may only be observed when non-equilibrium bath effects are taken into account. Furthermore, we illustrate how this formalism allows us to identify the electronic or vibrational origin of the oscillatory dynamics., Comment: 13 pages, 6 figures; minor corrections made; accepted for publication in Journal of Chemical Physics

Information about quantum phase transitions in conventional condensed matter systems, must be sought by probing the matter system itself. By contrast, we show that mixed matter-light systems offer a distinct advantage in that the photon field carries clear signatures of the associated quantum critical phenomena. Having derived an accurate, size-consistent Hamiltonian for the photonic field in the well-known Dicke model, we predict striking behavior of the optical squeezing and photon statistics near the phase transition. The corresponding dynamics resemble those of a degenerate parametric amplifier. Our findings boost the motivation for exploring exotic quantum phase transition phenomena in atom-cavity, nanostructure-cavity, and nanostructure-photonic-band-gap systems., Comment: 4 pages, 4 figures

Semiconductor quantum dots integrated with ultrafast spectroscopy technology are prime candidates for building scalable architectures for Quantum Information Processing. In this review paper we survey the current state of theoretical proposals concerning all-optical control of nanostructure qubits and their interactions. These schemes offer potential for ultrafast optical manipulation of quantum information in time scales within the coherence time., Comment: 36 pages, 9 figures. Review article to appear in "Handbook of Theoretical and Computational Nanotechnology"