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Quantum Coherence and Its Signatures in Extended Quantum Systems
journal contribution
posted on 2020-05-25, 04:48 authored by Rajesh Dutta, Biman BagchiQuantum
coherence controls almost every aspect of static and dynamic
response of a strongly correlated quantum system, although details
of this control have not been elucidated in many cases. We find that,
in the presence of a significant static off-diagonal coupling, quantum
coherence can survive much longer than the bath correlation time in
a noisy environment. In the presence of time correlated noise (non-Markovian
limit), coherence could propagate through the excited bath states,
and this plays a nontrivial role in giving rise to a noncanonical
temperature dependence of population distribution in an extended conjugated
polymer-like system. The quantum coherence through the excited bath
states vanishes in the high temperature limit, giving rise to the
equilibrium Boltzmann distribution. Second, we discuss a role of quantum
coherence in exciton localization that bears resemblance to Anderson
localization. Calculations have been carried out not only with a chain
of conjugated polymer but also with dimer and trimer subunits of the
Fenna–Matthews–Olson (FMO) complex. We derive an analytical
expression of the relation between steady state coherence and excitionic
population distribution. We analytically showed that steady state
coherence in equilibrium bath states is governed by interchromophoric
coupling (J) whereas coherence in excited bath states
is dictated by fluctuation strength (Vd) for the spatially correlated bath model. For the spatially uncorrelated
bath model, we observe that at the low temperature limit coherence
in the excited bath states dominates over coherence in equilibrium
bath states and vice versa. In the study of the localization problem,
we analytically show that, in the limit of a negligibly small fluctuation
rate (bd), the diffusion coefficient is
exactly proportional to the fluctuation rate, leading to complete
breakdown of the Haken–Strobl–Silbey Markovian prediction.
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bath statesbath correlation timeuncorrelated bath modelstate coherenceequilibrium Boltzmann distributionexcitionic population distributiontemperature limit coherenceExtended Quantum Systems Quantum coherence controlsquantum coherencefluctuation rateFMOnoncanonical temperature dependenceequilibrium bath states
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