When do perturbative approaches accurately capture the dynamics of complex quantum systems?

A quantum system weakly coupled to a zero-temperature environment will relax, via spontaneous emission, to its ground-state. However, when the coupling to the environment is ultra-strong the ground-state is expected to become dressed with virtual excitations. This regime is difficult to capture with some traditional methods because of the explosion in the number of Matsubara frequencies, i.e., exponential terms in the free-bath correlation function. To access this regime we generalize both the hierarchical equations of motion and pseudomode methods, taking into account this explosion using only a biexponential fitting function. We compare these methods to the reaction coordinate mapping, which helps show how these sometimes neglected Matsubara terms are important to regulate detailed balance and prevent the unphysical emission of virtual excitations. For the pseudomode method, we present a general proof of validity for the use of superficially unphysical Matsubara-modes, which mirror the mathematical essence of the Matsubara frequencies.

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“…Note again that this is not a generic construction [48], but is specific for the choice of decomposition of correlation functions we use here.…”

Section: The Hierarchical Equations Of Motionmentioning

confidence: 99%

Modelling the ultra-strongly coupled spin-boson model with unphysical modes

et al. 2019

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“…simple heat baths, that have been connected to (transient) phenomena such as violation of detailed balance, extension of electronic coherence times and vibronic mixing of electronic states 4,8,16,18,20,21,23,24,28,[40][41][42] . However, to describe the dissipative dynamics of systems coupled to such environments requires advanced numerical and analytical techniques, and approaches ranging from manybody methods to advanced master equation formulations have recently been applied or developed for this aim 13,19,[43][44][45][46][47][48][49][50][51][52][53][54][55][56] .…”

Section: Introductionmentioning

confidence: 99%

Coherent quantum dynamics launched by incoherent relaxation in a quantum circuit simulator of a light-harvesting complex

et al. 2018

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Engineering and harnessing coherent excitonic transport in organic nanostructures has recently been suggested as a promising way towards improving man-made light harvesting materials. However, realising and testing the dissipative system-environment models underlying these proposals is presently very challenging in supramolecular materials. A promising alternative is to use simpler and highly tunable 'quantum simulators' built from programmable qubits, as recently achieved in a superconducting circuit by Potočnik et al. Nature Communications, 9, 904 (2018) 1 . In this article, we simulate the real-time dynamics of an exciton coupled to a quantum bath as it moves through a network based on the quantum circuit of 1 . Using the numerically exact hierarchical equations of motion to capture the open quantum system dynamics, we find that an ultrafast but completely incoherent relaxation from a high-lying 'bright' exciton into a doublet of closely spaced 'dark' excitons can spontaneously generate electronic coherences and oscillatory real-space motion across the network (quantum beats). Importantly, we show that this behaviour also survives when the environmental noise is classically stochastic (effectively high temperature), as in present experiments. These predictions highlight the possibilities of designing matched electronic and spectral noise structures for robust coherence generation that doesn't require coherent excitation or cold environments. arXiv:1806.06087v1 [quant-ph]

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“…Such an enhancement indicates toward the possibility of two situations: (a) the preservation of memory by non‐Markovianity enhances the ETE or (b) the initial pure state relaxes efficiently to increase the trapping at RCC. To demonstrate the effect of non‐Markovianity, we have compared the ETE with both the Markovian and non‐Markovian master equation.…”

Section: Resultsmentioning

confidence: 99%

Role of Coherence in Excitation Transfer Efficiency to the Reaction Center in Photosynthetic Bacteria Chlorobium tepidum

Singh

Dasgupta

2019

ChemistrySelect

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We investigate the effect of coherence to the excitation transfer efficiency (ETE) in photosynthetic bacteria Chlorobium tepidum. We have modelled the monomer of Fenna‐Matthews‐Olson (FMO) complex as consisting of eight bacteriochlorophyll‐a sites, while explicitly consider reaction center core complex (RCC) as an additional site. With the use of realistic bath spectrum and several dominant vibronic modes in the non‐Markovian master equation, in an effective 9‐site model, we have compared the ETE for an initial pure state and an initial mixed state. We observe that the initial pure state relaxes efficiently to increase the trapping at the RCC. We further illustrate that the coherence play a competitive role to block the back transfer of excitation from RCC pigment to FMO complex and hence to maximize the ETE.

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When do perturbative approaches accurately capture the dynamics of complex quantum systems?

Cited by 28 publications

References 43 publications

Modelling the ultra-strongly coupled spin-boson model with unphysical modes

Modelling the ultra-strongly coupled spin-boson model with unphysical modes

Coherent quantum dynamics launched by incoherent relaxation in a quantum circuit simulator of a light-harvesting complex

Role of Coherence in Excitation Transfer Efficiency to the Reaction Center in Photosynthetic Bacteria Chlorobium tepidum

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