1,383 research outputs found
Transport Properties and Optical Conductivity of the adiabatic Su-Schrieffer-Heeger model: a showcase study for rubrene based field effect transistors
Transport properties, spectral function and optical conductivity of the
adiabatic one-dimensional Su-Schrieffer-Heeger (SSH) model are studied with
particular emphasis on the model parameters suitable for Rubrene single
crystals based field effect transistors. We show that the mobility, calculated
by using the Kubo formula for conductivity, vanishes unless we introduce an "ad
hoc" broadening of the system energy levels. Furthermore, the apparent
contradiction between angle resolved photoemission data and transport
properties is clarified by studying the behavior of the spectral function.
Finally, a peak in the optical conductivity at very low energy is obtained and
discussed in connection with the available experimental data for Rubrene based
devices
May a dissipative environment be beneficial for quantum annealing?
We discuss the quantum annealing of the fully-connected ferromagnetic -spin model in a dissipative environment at low temperature. This model, in
the large limit, encodes in its ground state the solution to the Grover's
problem of searching in unsorted databases. In the framework of the quantum
circuit model, a quantum algorithm is known for this task, providing a
quadratic speed-up with respect to its best classical counterpart. This
improvement is not recovered in adiabatic quantum computation for an isolated
quantum processor. We analyze the same problem in the presence of a
low-temperature reservoir, using a Markovian quantum master equation in
Lindblad form, and we show that a thermal enhancement is achieved in the
presence of a zero temperature environment moderately coupled to the quantum
annealer.Comment: 4 pages, 1 figure, proceeding of IQIS 201
Ballistic transport in one-dimensional loops with Rashba and Dresselhaus spin-orbit coupling
We discuss the combined effect of Rashba and Dresselhaus spin-orbit interactions in polygonal loops formed by quantum wires, when the electron are injected in a node and collected at the opposite one. The conditions that allow perfect localization are found. Furthermore, we investigate the suppression of the Al'tshuler--Aronov--Spivak oscillations that appear, in presence of a magnetic flux, when the electrons are injected and collected at the same node. Finally, we point out that a recent realization of a ballistic spin interferometer can be used to obtain a reliable estimate of the magnitude ratio of the two spin-orbit interactions.\bigski
Dynamical moments reveal a topological quantum transition in a photonic quantum walk
Many phenomena in solid-state physics can be understood in terms of their
topological properties. Recently, controlled protocols of quantum walks are
proving to be effective simulators of such phenomena. Here we report the
realization of a photonic quantum walk showing both the trivial and the
non-trivial topologies associated with chiral symmetry in one-dimensional
periodic systems, as in the Su-Schrieffer-Heeger model of polyacetylene. We
find that the probability distribution moments of the walker position after
many steps behave differently in the two topological phases and can be used as
direct indicators of the quantum transition: while varying a control parameter,
these moments exhibit a slope discontinuity at the transition point, and remain
constant in the non-trivial phase. Extending this approach to higher
dimensions, different topological classes, and other typologies of quantum
phases may offer new general instruments for investigating quantum transitions
in such complex systems
Going beyond Local and Global approaches for localized thermal dissipation
Identifying which master equation is preferable for the description of a
multipartite open quantum system is not trivial and has led in the recent years
to the local vs. global debate in the context of Markovian dissipation. We
treat here a paradigmatic scenario in which the system is composed of two
interacting harmonic oscillators A and B, with only A interacting with a
thermal bath - collection of other harmonic oscillators - and we study the
equilibration process of the system initially in the ground state with the bath
finite temperature. We show that the completely positive version of the
Redfield equation obtained using coarse-grain and an appropriate time-dependent
convex mixture of the local and global solutions give rise to the most accurate
semigroup approximations of the whole exact system dynamics, i.e. both at short
and at long time scales, outperforming the local and global approaches
Dynamical heat engines with non--Markovian reservoirs
We discuss whether, and under which conditions, it is possible to realize a
heat engine simply by dynamically modulating the couplings between the quantum
working medium and thermal reservoirs. For that purpose, we consider the
paradigmatic model of a quantum harmonic oscillator, exposed to a minimal
modulation, that is, a monochromatic driving of the coupling to only one of the
thermal baths. We demonstrate, at any order in the system/bath coupling
strength, that in this setup non--Markovianity of the bath is a necessary
condition to obtain a heat engine. In addition, we identify suitable structured
environments for the engine to approach the ideal Carnot efficiency. Our
results open up new possibilities for the use of non--Markovian open quantum
systems for the construction and optimization of quantum thermal machines.Comment: Final revision as published on Physical Review Research: 19 pages, 7
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