2,986 research outputs found
Quantum theory of the low-frequency linear susceptibility of interferometer-type superconducting qubits
We use the density matrix formalism to analyze the interaction of
interferometer-type superconducting qubits with a high quality tank circuit,
which frequency is well below the gap frequency of a qubit. We start with the
ground state characterization of the superconducting flux and charge qubits.
Then, by making use of a dressed state approach we describe the qubits'
spectroscopy when the qubit is irradiated by a microwave field which is tuned
to the gap frequency. The last section of the paper is devoted to continuous
monitoring of qubit states by using a DC SQUID in the inductive mode.Comment: 11 pages, 5 figures; the title and abstract are slightly changed;
several typos are corrected; in order to make our argumentation more clear we
added some comments in the introduction and other section
Low frequency Rabi spectroscopy for a dissipative two-level system
We have analyzed the interaction of a dissipative two level quantum system
with high and low frequency excitation. The system is continuously and
simultaneously irradiated by these two waves. If the frequency of the first
signal is close to the level separation the response of the system exhibits
undamped low frequency oscillations whose amplitude has a clear resonance at
the Rabi frequency with the width being dependent on the damping rates of the
system. The method can be useful for low frequency Rabi spectroscopy in various
physical systems which are described by a two level Hamiltonian, such as nuclei
spins in NMR, double well quantum dots, superconducting flux and charge qubits,
etc. As the examples, the application of the method to a nuclear spin and to
the readout of a flux qubit are briefly discussed.Comment: 4 pages, 3 figures, the figures are modifie
Switching the current through molecular wires
The influence of Gaussian laser pulses on the transport through molecular
wires is investigated within a tight-binding model for spinless electrons
including correlation. Motivated by the phenomenon of coherent destruction of
tunneling for monochromatic laser fields, situations are studied in which the
maximum amplitude of the electric field fulfills the conditions for the
destructive quantum effect. It is shown that, as for monochromatic laser
pulses, the average current through the wire can be suppressed. For parameters
of the model, which do not show a net current without any optical field, a
Gaussian laser pulse can establish a temporary current. In addition, the effect
of electron correlation on the current is investigated.Comment: 8 pages, 6 figure
The Use of CIR and Airborne Multispectral Scanner Techniques for Wetland Soils Mapping of Highway Corridors
This paper summarizes the results of an investigation aimed at evaluating the potential advantages of state-of-the-art airborne remote sensing for highway siting and planning tasks, specifically in wetlands areas.
The basic objectives of the study were to develop methodologies using remotely sensed data for mapping wetlands soils and drainage, to evaluate the relative merits and usefulness of the various methods developed, to generate a selection of output products from the remote sensor data for display to highway planners and photo-interpreters, and to provide recommendations for implementation of remote sensing techniques in the highway planning and siting process. To accomplish these objectives, remote sensor and ground truth data were acquired for selected test sites in Florida, Michigan, and Minnesota. One of several test sites in Michigan has been selected as representative of the study objectives and methodology
Highly efficient energy excitation transfer in light-harvesting complexes: The fundamental role of noise-assisted transport
Excitation transfer through interacting systems plays an important role in
many areas of physics, chemistry, and biology. The uncontrollable interaction
of the transmission network with a noisy environment is usually assumed to
deteriorate its transport capacity, especially so when the system is
fundamentally quantum mechanical. Here we identify key mechanisms through which
noise such as dephasing, perhaps counter intuitively, may actually aid
transport through a dissipative network by opening up additional pathways for
excitation transfer. We show that these are processes that lead to the
inhibition of destructive interference and exploitation of line broadening
effects. We illustrate how these mechanisms operate on a fully connected
network by developing a powerful analytical technique that identifies the
invariant (excitation trapping) subspaces of a given Hamiltonian. Finally, we
show how these principles can explain the remarkable efficiency and robustness
of excitation energy transfer from the light-harvesting chlorosomes to the
bacterial reaction center in photosynthetic complexes and present a numerical
analysis of excitation transport across the Fenna-Matthew-Olson (FMO) complex
together with a brief analysis of its entanglement properties. Our results show
that, in general, it is the careful interplay of quantum mechanical features
and the unavoidable environmental noise that will lead to an optimal system
performance.Comment: 16 pages, 9 figures; See Video Abstract at
http://www.quantiki.org/video_abstracts/09014454 . New revised version;
discussion of entanglement properties enhance
Coherent Transport through an interacting double quantum dot: Beyond sequential tunneling
Various causes for negative differential conductance in transport through an
interacting double quantum dot are investigated. Particular focus is given to
the interplay between the renormalization of the energy levels due to the
coupling to the leads and the decoherence of the states. The calculations are
performed within a basis of many-particle eigenstates and we consider the
dynamics given by the von Neumann-equation taking into account also processes
beyond sequential tunneling. A systematic comparison between the levels of
approximation and also with different formalisms is performed. It is found that
the current is qualitatively well described by sequential processes as long as
the temperature is larger than the level broadening induced by the contacts.Comment: 11 pages, 5 figures included in tex
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