7,857 research outputs found
Genomics and synthetic biology as a viable option to intensify sustainable use of biodiversity
The Amazon basin is an area of mega-biodiversity. Different models have been proposed^1-8^ for the establishment of an effective conservation policy, increasing sustainability and adding value for biodiversity. Currently, a broad spectrum of technologies from genomics to synthetic biology is available, and these permit the collection, manipulation and effective evaluation of countless organisms, metabolic pathways and molecules that exist as potential products of a large, biodiverse ecosystem. The use of Genomics and synthetic biology may constitute an important tool and be a viable option for the prospection, evaluation and manipulation of biodiversity as advocated as well as be useful for developing methods for sustainable use and the production of novel molecules
Measurement back-action on adiabatic coherent electron transport
We study the back-action of a nearby measurement device on electrons
undergoing coherent transfer via adiabatic passage (CTAP) in a triple-well
system. The measurement is provided by a quantum point contact capacitively
coupled to the middle well, thus acting as a detector sensitive to the charge
configuration of the triple-well system. We account for this continuous
measurement by treating the whole {triple-well + detector} as a closed quantum
system. This leads to a set of coupled differential equations for the density
matrix of the enlarged system which we solve numerically. This approach allows
to study a single realization of the measurement process while keeping track of
the detector output, which is especially relevant for experiments. In
particular, we find the emergence of a new peak in the distribution of
electrons that passed through the point contact. As one increases the coupling
between the middle potential well and the detector, this feature becomes more
prominent and is accompanied by a substantial drop in the fidelity of the CTAP
scheme
Site-centered impurities in quantum spin chains
The magnetic behavior of antiferromagnetic spin 1/2 chains with site-centered
impurities in a magnetic field is investigated. The effect of impurities is
implemented by considering different situations of both diagonal and
off-diagonal disorder. The resulting magnetization curves present a wide
variety of plateaux, whose position strongly depends on the kind of disorder
considered. The relevance of these results to experimental situations is also
discussed.Comment: 6 pages, 6 figure
Transport properties of partially equilibrated quantum wires
We study the effect of thermal equilibration on the transport properties of a
weakly interacting one-dimensional electron system. Although equilibration is
severely suppressed due to phase-space restrictions and conservation laws, it
can lead to intriguing signatures in partially equilibrated quantum wires. We
consider an ideal homogeneous quantum wire. We find a finite temperature
correction to the quantized conductance, which for a short wire scales with its
length, but saturates to a length-independent value once the wire becomes
exponentially long. We also discuss thermoelectric properties of long quantum
wires. We show that the uniform quantum wire is a perfect thermoelectric
refrigerator, approaching Carnot efficiency with increasing wire length.Comment: 20 pages, 6 figure
Resistivity of inhomogeneous quantum wires
We study the effect of electron-electron interactions on the transport in an
inhomogeneous quantum wire. We show that contrary to the well-known Luttinger
liquid result, non-uniform interactions contribute substantially to the
resistance of the wire. In the regime of weakly interacting electrons and
moderately low temperatures we find a linear in T resistivity induced by the
interactions. We then use the bosonization technique to generalize this result
to the case of arbitrarily strong interactions.Comment: 4 pages, 1 figur
Current and noise correlations in a double dot Cooper pair beam splitter
We consider a double quantum dot coupled to two normal leads and one
superconducting lead, modeling the Cooper pair beam splitter studied in two
recent experiments. Starting from a microscopic Hamiltonian we derive a general
expression for the branching current and the noise crossed correlations in
terms of single and two-particle Green's function of the dot electrons. We then
study numerically how these quantities depend on the energy configuration of
the dots and the presence of direct tunneling between them, isolating the
various processes which come into play. In absence of direct tunneling, the
antisymmetric case (the two levels have opposite energies with respect to the
superconducting chemical potential) optimizes the Crossed Andreev Reflection
(CAR) process while the symmetric case (the two levels have the same energies)
favors the Elastic Cotunneling (EC) process. Switching on the direct tunneling
tends to suppress the CAR process, leading to negative noise crossed
correlations over the whole voltage range for large enough direct tunneling
Interactions and charge fractionalization in an electronic Hong-Ou-Mandel interferometer
We consider an electronic analog of the Hong-Ou-Mandel (HOM) interferometer,
where two single electrons travel along opposite chiral edge states and collide
at a Quantum Point Contact. Studying the current noise, we show that because of
interactions between co-propagating edge states, the degree of
indistinguishability between the two electron wavepackets is dramatically
reduced, leading to reduced contrast for the HOM signal. This decoherence
phenomenon strongly depends on the energy resolution of the packets. Insofar as
interactions cause charge fractionalization, we show that charge and neutral
modes interfere with each other, leading to satellite dips or peaks in the
current noise. Our calculations explain recent experimental results [E.
Bocquillon, et al., Science 339, 1054(2013)] where an electronic HOM signal
with reduced contrast was observed.Comment: 5 pages, 2 figure
Real-time simulation of finite frequency noise from a single electron emitter
We study the real-time emission of single electrons from a quantum dot
coupled to a one dimensional conductor, using exact diagonalization on a
discrete tight-binding chain. We show that from the calculation of the
time-evolution of the one electron states, we have a simple access to all the
relevant physical quantities in the system. In particular, we are able to
compute accurately the finite frequency current autocorrelation noise. The
method which we use is general and versatile, allowing to study the impact of
many different parameters like the dot transparency or level position. Our
results can be directly compared with existing experiments, and can also serve
as a basis for future calculations including electronic interactions using the
time dependent density-matrix renormalisation group and other techniques based
on tight-binding models.Comment: 10 page
Current correlations in the interacting Cooper-pair beam-splitter
We propose an approach allowing the computation of currents and their
correlations in interacting multiterminal mesoscopic systems involving quantum
dots coupled to normal and/or superconducting leads. The formalism relies on
the expression of branching currents and noise crossed correlations in terms of
one- and two-particle Green's functions for the dots electrons, which are then
evaluated self-consistently within a conserving approximation. We then apply
this to the Cooper-pair beam-splitter setup recently proposed [L. Hofstetter et
al. Nature (London) 461 960 (2009); Phys. Rev. Lett. 107 136801 (2011); L. G.
Herrmann et al. Phys. Rev. Lett. 104 026801 (2010)], which we model as a double
quantum dot with weak interactions, connected to a superconducting lead and two
normal ones. Our method not only enables us to take into account a local
repulsive interaction on the dots, but also to study its competition with the
direct tunneling between dots. Our results suggest that even a weak Coulomb
repulsion tends to favor positive current cross correlations in the
antisymmetric regime (where the dots have opposite energies with respect to the
superconducting chemical potential)
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