4,219 research outputs found
Spin-flip phonon-mediated charge relaxation in double quantum dots
We theoretically study the triplet to singlet relaxation rate
in a lateral gate-defined double quantum dot tuned to the regime of Pauli spin
blockade. We present a detailed derivation of the effective phonon density of
states for this specific charge transition, keeping track of the contribution
from piezoelectric as well as deformation potential electron-phonon coupling.
We further investigate two different spin-mixing mechanisms which can couple
the triplet and singlet states: a magnetic field gradient over the double dot
(relevant at low external magnetic field) and spin-orbit interaction (relevant
at high field), and we also indicate how the two processes could interfere at
intermediate magnetic field. Finally, we show how to combine all results and
evaluate the relaxation rate for realistic system parameters.Comment: 9 pages, 4 figure
Leakage and dephasing in Si-based exchange-only spin qubits
Exchange-only spin qubits hosted in Si-based triple quantum dots do
not suffer from decoherence caused by randomly fluctuating nuclear-spin
ensembles and can be relatively robust against electrical noise when operated
at a sweet spot. Remaining sources of decoherence are qubit relaxation, leakage
out of the qubit subspace, and dephasing due to residual effects of charge
noise, the latter two of which are the focus of this work. We investigate
spin-orbit-mediated leakage rates to the three-spin ground state accompanied by
virtual (i) tunneling, (ii) orbital excitation, and (iii) valley excitation of
an electron. We find different power-law dependencies on the applied magnetic
field for the three mechanisms as well as for the two leakage rates,
ranging from to , and identify the sweet spot as
a point of minimal leakage. We also revisit the role of electrical noise at the
sweet spot, and show that it causes a decay of coherent qubit oscillations that
follows a power law (as opposed to the more common exponential
decay) and introduces a phase shift.Comment: 10 pages, three figures. Minor changes with respect to the previous
version. The supplemental material is now included as appendice
Community Structure in Jazz
Using a database of jazz recordings we study the collaboration network of
jazz musicians. We define the network at two different levels. First we study
the collaboration network between individuals, where two musicians are
connected if they have played in the same band. Then we consider the
collaboration between bands, where two bands are connected if they have a
musician in common. The community structure analysis reveals that these
constructions capture essential ingredients of the social interactions between
jazz musicians. We observe correlations between recording locations, racial
segregation and the community structure. A quantitative analysis of the
community size distribution reveals a surprising similarity with an e-mail
based social network recently studied.Comment: 12 pages, 6 figures, Revtex4 format, Acknowledgments update
Multi-level interference resonances in strongly-driven three-level systems
We study multi-photon resonances in a strongly-driven three-level quantum
system, where one level is periodically swept through a pair of levels with
constant energy separation . Near the multi-photon resonance condition
, where is an integer, we find qualitatively different
behavior for even or odd. We explain this phenomenon in terms of families
of interfering trajectories of the multi-level system. Remarkably, the behavior
is insensitive to fluctuations of the energy of the driven level, and survives
deep into the strong dephasing regime. The setup can be relevant for a variety
of solid state and atomic or molecular systems. In particular, it provides a
clear mechanism to explain recent puzzling experimental observations in
strongly-driven double quantum dots.Comment: 4 pages, 3 figure
Semiclassical theory of persistent current fluctuations in ballistic chaotic rings
The persistent current in a mesoscopic ring has a Gaussian distribution with
small non-Gaussian corrections. Here we report a semiclassical calculation of
the leading non-Gaussian correction, which is described by the three-point
correlation function. The semiclassical approach is applicable to systems in
which the electron dynamics is ballistic and chaotic, and includes the
dependence on the Ehrenfest time. At small but finite Ehrenfest times, the
non-Gaussian fluctuations are enhanced with respect to the limit of zero
Ehrenfest time.Comment: 9 pages, 3 figures; submitted as invited contribution to a special
issue in Physica E in memory of Markus Buettike
Impact of community structure on information transfer
The observation that real complex networks have internal structure has important implication for dynamic processes occurring on such topologies. Here we investigate the impact of community structure on a model of information transfer able to deal with both search and congestion simultaneously. We show that networks with fuzzy community structure are more efficient in terms of packet delivery than those with pronounced community structure. We also propose an alternative packet routing algorithm which takes advantage of the knowledge of communities to improve information transfer and show that in the context of the model an intermediate level of community structure is optimal. Finally, we show that in a hierarchical network setting, providing knowledge of communities at the level of highest modularity will improve network capacity by the largest amount
Conductance spectroscopy on Majorana wires and the inverse proximity effect
Recent experimental searches for signatures of Majorana-like excitations in
proximitized semiconducting nanowires involve conductance spectroscopy, where
the evidence sought after is a robust zero-bias peak (in longer wires) and its
characteristic field-dependent splitting (in shorter wires). Although
experimental results partially confirm the theoretical predictions, commonly
observed discrepancies still include (i) a zero-bias peak that is significantly
lower than the predicted value of and (ii) the absence of the expected
"Majorana oscillations" of the lowest-energy modes at higher magnetic fields.
Here, we investigate how the inevitable presence of a normal drain lead
connected to the hybrid wire can affect the conductance spectrum of the hybrid
wire. We present numerical results using a one-band model for the proximitized
nanowire, where the superconductor is considered to be in the diffusive regime,
described by semi-classical Green functions. We show how the presence of the
normal drain could (at least partially) account for the observed discrepancies,
and we complement this with analytic results providing more insights in the
underlying physics.Comment: 10 pages, 7 figure
Spin-wave-induced correction to the conductivity of ferromagnets
We calculate the correction to the conductivity of a disordered ferromagnetic
metal due to spin-wave-mediated electron--electron interactions. This
correction is the generalization of the Altshuler-Aronov correction to
spin-wave-mediated interactions. We derive a general expression for the
conductivity correction to lowest order in the spin-wave-mediated interaction
and for the limit that the exchange splitting is much smaller than the
Fermi energy. For a "clean" ferromagnet with ,
with the mean time for impurity scattering, we find a
correction at temperatures above the spin
wave gap. In the opposite, "dirty" limit, ,
the correction is a non-monotonous function of temperature.Comment: 9 pages, 6 figure
Risk based capital allocation
In this paper, we focus on the economic research of corruption. In the first part, we define corruption, types of corruption, its factors and ways to measure it. This section brings together various definitions by notable authors of this domain, such as Begovic, Tanzi, Mauro or Lambsdorff. Before moving to the second section, we are presenting definitions, typologies and factors already researched by acclaimed authors. In the second part, we focus on the channels by which corruption transmits its effects through the economy. This section consists of two major sub-parts, the first one in which we take part in a vivid scientific discussion with the ââapologistsââ of corruption, i.e. with those economists who underline positive roles of corruption. In the second sub-part of the second section, as a logic continuation of the previous sub-part, we are listing three important consequences of rampant corruption in one economy: consequences to economic growth, foreign direct investments and economic efficiency. Major contribution of this paper is compilation of significant scientific discoveries in the area, as well as bringing new arguments in the discussion on the economic consequences of corruption. The paper uses traditional approach of the New institutional economics (NIE), by underlining the importance of governance, transaction costs and rent seeking.corruption, institutional capacities, new institutional economics, transaction costs, FDI
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