25 research outputs found
The Molecular Photo-Cell: Quantum Transport and Energy Conversion at Strong Non-Equilibrium
Non-equilibrium transport properties and energy conversion performance of a
molecular photo-voltaic cell are analyzed using the Lindblad master equation
within the open quantum systems approach. The method allows us to calculate the
dynamics of a system driven by several non-equilibrium sources (a situation we
call "strong non-equilibrium"), which is the natural operating condition of
photovoltaic cells. We include both coherent and incoherent processes and treat
electrons, photon, and phonons on an equal footing. We find that decoherence
plays a crucial role in determining both the overall efficiency of the
photovoltaic conversion and the optimal energy configuration of the system.
Specifically, decoherence leads to better performance, due to a faster
relaxation of the excited electrons to the electrodes. We also examine the
effect of coherent interference on the efficiency. The approach we propose in
this letter is suitable for studying transport and energy conversion in other
nanoscale systems at non-equilibrium, where both coherent and incoherent
processes take place.Comment: 5+ pages, 4 figures, Sci. Rep. In press (with additional
supplementary information there
Nonequilibrium Quantum Phase Transitions in the XY model: comparison of unitary time evolution and reduced density matrix approaches
We study nonequilibrium quantum phase transitions in XY spin 1/2 chain using
the algebra. We show that the well-known quantum phase transition at
magnetic field persists also in the nonequilibrium setting as long as
one of the reservoirs is set to absolute zero temperature. In addition, we find
nonequilibrium phase transitions associated to imaginary part of the
correlation matrix for any two different temperatures of the reservoirs at and , where is the anisotropy and
the magnetic field strength. In particular, two nonequilibrium quantum
phase transitions coexist at . In addition we also study the quantum
mutual information in all regimes and find a logarithmic correction of the area
law in the nonequilibrium steady state independent of the system parameters. We
use these nonequilibrium phase transitions to test the utility of two models of
reduced density operator, namely Lindblad mesoreservoir and modified Redfield
equation. We show that the nonequilibrium quantum phase transition at
related to the divergence of magnetic susceptibility is recovered in the
mesoreservoir approach, whereas it is not recovered using the Redfield master
equation formalism. However none of the reduced density operator approaches
could recover all the transitions observed by the algebra. We also study
thermalization properties of the mesoreservoir approach.Comment: 25 pages, 10 figure
Reconnection of Stable/Unstable Manifolds of the Harper Map
The Harper map is one of the simplest chaotic systems exhibiting reconnection
of invariant manifolds. The method of asymptotics beyond all orders (ABAO) is
used to construct stable/unstable manifolds of the Harper map. When the
parameter changes to the reconnection threshold, the stable/unstable manifolds
are shown to acquire new oscillatory portion corresponding to the heteroclinic
tangle after the reconnection.Comment: 24 pages, 11 figure
Nonequilibrium Peierls Transition
Nonequlibrium phase transition of an open Takayama-Lin Liu-Maki chain coupled
with two reservoirs is investigated by combining a mean-field approximation and
a formula characterizing nonequlibrium steady states, which is obtained from
the algebraic field approach to nonequlibrium statistical mechanics. When the
bias voltage is chosen to be a control parameter, the phase transition between
ordered and normal phases is found to be first or second order. Then, the
voltage-current characteristics is S-shaped in some parameter region. In
contrast, when the current is chosen to be a control parameter, all the
non-trivial solutions of the self-consistent equation are found to become
stable. In this case, the phase transition between the ordered and normal
phases is always second order and negative differential conductivity appears at
low temperature.Comment: 30 pages, 21 frigure
Current in coherent quantum systems connected to mesoscopic Fermi reservoirs
We study particle current in a recently proposed model for coherent quantum transport. In this model, a system connected to mesoscopic Fermi reservoirs (meso-reservoir) is driven out of equilibrium by the action of super-reservoirs thermalized to prescribed temperatures and chemical potentials by a simple dissipative mechanism described by the Lindblad equation. We compare exact (numerical) results with theoretical expectations based on the Landauer formula
Reconnection of Stable/Unstable Manifolds of the Harper Map(6) Approaches from mathematical science and quantum information, Chaos and Nonlinear Dynamics in Quantum-Mechanical and Macroscopic Systems)
この論文は国立情報学研究所の電子図書館事業により電子化されました。Harper方程式は、パラメーターの変化によりセパラトリックスのつなぎ変えを起こす最も簡単なモデルのひとつである(リコネクション)。Harper方程式の時間を離散化したHarper写像において安定/不安定多様体の公式を解析的に導いた。これにより、両多様体はリコネクションが起こるパラメーター付近でリコネクションの前駆となる振動を始めることを示した