324 research outputs found
Entangled Wavefunctions from Classical Oscillator Amplitudes
In the first days of quantum mechanics Dirac pointed out an analogy between
the time-dependent coefficients of an expansion of the Schr\"odinger equation
and the classical position and momentum variables solving Hamilton's equations.
Here it is shown that the analogy can be made an equivalence in that, in
principle, systems of classical oscillators can be constructed whose position
and momenta variables form time-dependent amplitudes which are identical to the
complex quantum amplitudes of the coupled wavefunction of an N-level quantum
system with real coupling matrix elements. Hence classical motion can reproduce
quantum coherence.Comment: extended versio
Recommendations for Future Efforts in RANS Modeling and Simulation
The roadmap laid out in the CFD Vision 2030 document suggests that a decision to move away from RANS research needs to be made in the current timeframe (around 2020). This paper outlines industry requirements for improved predictions of turbulent flows and the cost-barrier that is often associated with reliance on scale resolving methods. Capabilities of RANS model accuracy for simple and complex flow flow fields are assessed, and modeling practices that degrade predictive accuracy are identified. Suggested research topics are identified that have the potential to improve the applicability and accuracy of RANS models. We conclude that it is important that some part of a balanced turbulence modeling research portfolio should include RANS efforts
Non-Markovian quantum state diffusion for absorption spectra of molecular aggregates
In many molecular systems one encounters the situation where electronic
excitations couple to a quasi-continuum of phonon modes. That continuum may be
highly structured e.g. due to some weakly damped high frequency modes. To
handle such a situation, an approach combining the non-Markovian quantum state
diffusion (NMQSD) description of open quantum systems with an efficient but
abstract approximation was recently applied to calculate energy transfer and
absorption spectra of molecular aggregates [Roden, Eisfeld, Wolff, Strunz, PRL
103 (2009) 058301]. To explore the validity of the used approximation for such
complicated systems, in the present work we compare the calculated
(approximative) absorption spectra with exact results. These are obtained from
the method of pseudomodes, which we show to be capable of determining the exact
spectra for small aggregates and a few pseudomodes. It turns out that in the
cases considered, the results of the two approaches mostly agree quite well.
The advantages and disadvantages of the two approaches are discussed
Adiabatic entanglement transport in Rydberg aggregates
We consider the interplay between excitonic and atomic motion in a regular,
flexible chain of Rydberg atoms, extending our recent results on entanglement
transport in Rydberg chains [W\"uster et al., Phys.Rev.Lett 105 053004 (2010)].
In such a Rydberg chain, similar to molecular aggregates, an electronic
excitation is delocalised due to long range dipole-dipole interactions among
the atoms. The transport of an exciton that is initially trapped by a chain
dislocation is strongly coupled to nuclear dynamics, forming a localised pulse
of combined excitation and displacement. This pulse transfers entanglement
between dislocated atoms adiabatically along the chain. Details about the
interaction and the preparation of the initial state are discussed. We also
present evidence that the quantum dynamics of this complex many-body problem
can be accurately described by selected quantum-classical methods, which
greatly simplify investigations of excitation transport in flexible chains
Influence of Complex Exciton-Phonon Coupling on Optical Absorption and Energy Transfer of Quantum Aggregates
We present a theory that efficiently describes the quantum dynamics of an
electronic excitation that is coupled to a continuous, highly structured phonon
environment. Based on a stochastic approach to non-Markovian open quantum
systems, we develop a dynamical framework that allows us to handle realistic
systems where a fully quantum treatment is desired yet the usual approximation
schemes fail. The capability of the method is demonstrated by calculating
spectra and energy transfer dynamics of mesoscopic molecular aggregates,
elucidating the transition from fully coherent to incoherent transfer
Light transport in PT-invariant photonic structures with hidden symmetries
We introduce a recursive bosonic quantization technique for generating
classical PT photonic structures that possess hidden symmetries and higher
order exceptional points. We study light transport in these geometries and we
demonstrate that perfect state transfer is possible only for certain initial
conditions. Moreover, we show that for the same propagation direction, left and
right coherent transports are not symmetric with field amplitudes following two
different trajectories. A general scheme for identifying the conservation laws
in such PT-symmetric photonic networks is also presented
Dynamics of a nano-scale rotor driven by single-electron tunneling
We investigate theoretically the dynamics and the charge transport properties
of a rod-shaped nano-scale rotor, which is driven by a similar mechanism as the
nanomechanical single-electron transistor (NEMSET). We show that a static
electric potential gradient can lead to self-excitation of oscillatory or
continuous rotational motion. The relevant parameters of the device are
identified and the dependence of the dynamics on these parameters is studied.
We further discuss how the dynamics is related to the measured current through
the device. Notably, in the oscillatory regime, we find a negative differential
conductance. The current-voltage characteristics can be used to infer details
of the surrounding environment which is responsible for damping
Suppression of quantum oscillations and the dependence on site energies in electronic excitation transfer in the Fenna-Matthews-Olson trimer
Energy transfer in the photosynthetic complex of the Green Sulfur Bacteria
known as the Fenna-Matthews-Olson (FMO) complex is studied theoretically taking
all three subunits (monomers) of the FMO trimer and the recently found eighth
bacteriochlorophyll (BChl) molecule into account. We find that in all
considered cases there is very little transfer between the monomers. Since it
is believed that the eighth BChl is located near the main light harvesting
antenna we look at the differences in transfer between the situation when BChl
8 is initially excited and the usually considered case when BChl 1 or 6 is
initially excited. We find strong differences in the transfer dynamics, both
qualitatively and quantitatively. When the excited state dynamics is
initialized at site eight of the FMO complex, we see a slow exponential-like
decay of the excitation. This is in contrast to the oscillations and a
relatively fast transfer that occurs when only seven sites or initialization at
sites 1 and 6 is considered. Additionally we show that differences in the
values of the electronic transition energies found in the literature lead to a
large difference in the transfer dynamics
Motion of Rydberg atoms induced by resonant dipole-dipole interactions
We show that nuclear motion of Rydberg atoms can be induced by resonant
dipole-dipole interactions that trigger the energy transfer between two
energetically close Rydberg states. How and if the atoms move depends on their
initial arrangement as well as on the initial electronic excitation. Using a
mixed quantum/classical propagation scheme we obtain the trajectories and
kinetic energies of atoms, initially arranged in a regular chain and prepared
in excitonic eigenstates. The influence of off-diagonal disorder on the motion
of the atoms is examined and it is shown that irregularity in the arrangement
of the atoms can lead to an acceleration of the nuclear dynamics
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