2,299 research outputs found
Current in nanojunctions : Effects of reservoir coupling
We study the effect of system reservoir coupling on currents flowing through
quantum junctions. We consider two simple double-quantum dot configurations
coupled to two external fermionic reservoirs and study the net current flowing
between the two reservoirs. The net current is partitioned into currents
carried by the eigenstates of the system and by the coherences between the
eigenstates induced due to coupling with the reservoirs. We find that current
carried by populations is always positive whereas current carried by coherences
are negative for large couplings. This results in a non-monotonic dependence of
the net current on the coupling strength. We find that in certain cases, the
net current can vanish at large couplings due to cancellation between currents
carried by the eigenstates and by the coherences. These results provide new
insights into the non-trivial role of system-reservoir couplings on electron
transport through quantum dot junctions. In the presence of weak coulomb
interactions, net current as a function of system reservoir coupling strength
shows similar trends as for the non-interacting case.Comment: 9 pages, 12 figure
Statistics of an adiabatic charge pump
We investigate the effect of time-dependent cyclic-adiabatic driving on the
charge transport in quantum junction. We propose a nonequilibrium Greens
function formalism to study statistics of the charge pumped (at zero bias)
through the junction. The formulation is used to demonstrate charge pumping in
a single electronic level coupled to two (electronic) reservoirs with time
dependent couplings. Analytical expression for the average pumped current for a
general cyclic driving is derived. It is found that for zero bias, for a
certain class of driving, the Berry phase contributes only to the odd
cumulants. To contrast, a quantum master equation formulation does not show
Berry-phase effect at all
Statistics of heat transport across capacitively coupled double quantum dot circuit
We study heat current and the full statistics of heat fluctuations in a
capacitively-coupled double quantum dot system. This work is motivated by
recent theoretical studies and experimental works on heat currents in quantum
dot circuits. As expected intuitively, within the (static) mean-field
approximation, the system at steady-state decouples into two single-dot
equilibrium systems with renormalized dot energies, leading to zero average
heat flux and fluctuations. This reveals that dynamic correlations induced
between electrons on the dots is solely responsible for the heat transport
between the two reservoirs. To study heat current fluctuations, we compute
steady-state cumulant generating function for heat exchanged between reservoirs
using two approaches : Lindblad quantum master equation approach, which is
valid for arbitrary coulomb interaction strength but weak system-reservoir
coupling strength, and the saddle point approximation for Schwinger-Keldysh
coherent state path integral, which is valid for arbitrary system-reservoir
coupling strength but weak coulomb interaction strength. Using thus obtained
generating functions, we verify steady-state fluctuation theorem for stochastic
heat flux and study the average heat current and its fluctuations. We find that
the heat current and its fluctuations change non-monotonically with the coulomb
interaction strength () and system-reservoir coupling strength ()
and are suppressed for large values of and .Comment: 14 pages, 6 figure
Statistics of work done in degenerate parametric amplification process
We study statistics of work done by two classical electric field pumps
(two-photon and one-photon resonant pumps) on a quantum optical oscillator. We
compute moment generating function for the energy change of the oscillator,
interpreted as work done by the classical drives on the quantum oscillator
starting out in a thermalized Boltzmann state. The moment generating function
is inverted, analytically when only one of the pumps is turned on and
numerically when both the pumps are turned on, to get the probability function
for the work. The resulting probability function for the work done by the
classical drive is shown to satisfy transient detailed and integral work
fluctuation theorems. Interestingly, we find that, in order for the work
distribution function to satisfy the fluctuation theorem in presence of both
the drivings, relative phase of drivings need to be shifted by , this is
related to the broken time reversal symmetry of the Hamiltonian.Comment: 10 pages, 8 figur
Growing Attributed Networks through Local Processes
This paper proposes an attributed network growth model. Despite the knowledge
that individuals use limited resources to form connections to similar others,
we lack an understanding of how local and resource-constrained mechanisms
explain the emergence of rich structural properties found in real-world
networks. We make three contributions. First, we propose a parsimonious and
accurate model of attributed network growth that jointly explains the emergence
of in-degree distributions, local clustering, clustering-degree relationship
and attribute mixing patterns. Second, our model is based on biased random
walks and uses local processes to form edges without recourse to global network
information. Third, we account for multiple sociological phenomena: bounded
rationality, structural constraints, triadic closure, attribute homophily, and
preferential attachment. Our experiments indicate that the proposed Attributed
Random Walk (ARW) model accurately preserves network structure and attribute
mixing patterns of six real-world networks; it improves upon the performance of
eight state-of-the-art models by a statistically significant margin of 2.5-10x.Comment: 11 pages, 13 figure
International Migration, Remittances and its Macroeconomic Impact on Indian Economy
This paper tried to study the impact of remittances on various macroeconomic and developmental aspects for the Indian economy. For this, the data regarding remittances and some of the macroeconomic variables like GDP, PFCE, GDFC, savings, FDI, FII, export, import and balance of trade deficit etc have been analyzed for the period 1971-2008. The study shows that remittances have been consistently increasing at very fast rate for the last 15 years which have significant implications on the above mentioned macroeconomic variables. Through this study, the importance of remittances as a source of external development finance has been discussed. At last, some of the regulatory frameworks governing the flow of remittances have also been discussed.
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