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

Abstract

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]

Role of the multiple-excitation manifold in a driven quantum simulator of an antenna complex

“…This situation, known as vibrationally assisted electronic decay or "phonon antenna" due to a sharply structured spectral density, has been studied in the context of EET in several different contexts [3,39,[66][67][68]. The bath-induced population-to-coherence process already predicted by nonsecular Redfield theory has been confirmed by HEOM simulations in the strong-coupling regime [65]. We showed that this generation of electronic coherence is the most efficient for a regime between weak and strong system-bath couplings, which is a general observation across the various types of biological "noise-assisted" transport that have been studied.…”

“…In a recent work, we have used numerically exact hierarchical equations of motion (HEOM) [33,[56][57][58][59][60][61][62][63][64] to predict the ultrafast generation of electronic coherences during the incoherent relaxation of a high-lying excitonic state into a doublet of nearly degenerate low-lying states [65]. This process could be realized in the particular configuration of the SC qubit circuit of Potočnik et al [53] in the following way: Intersite couplings and gaps are chosen so that the firstexcited manifold consists in a bright state (optically excitable) separated from a doublet of dark (nonradiative) states such that the bright-dark energy gap is in resonance with a sharply peaked spectral density of the noise.…”

Quantum simulation of clustered photosynthetic light harvesting in a superconducting quantum circuit

“…Coupled to some specific qubit, the TLR can act as a reaction center through Purcell-like coupling. 40,41 By tuning the TLR's decay time and the qubit-TLR detuning, we can effectively modified the qubit's decay time through Purcell-like coupling, according to Equation (18).…”

“…On the other hand, much progress has been made in quantum information science, inspiring several interesting quantum simulation 35,36 experiments to verify the design principles for optimal light-harvesting. 28,29,[37][38][39][40][41][42] By using bath engineering and the gradient ascent pulse engineering algorithm, Wang et al 37 performed an experimental quantum simulation of photosynthetic energy transfer by using nuclear magnetic resonance (NMR). It was demonstrated that the open quantum dynamics in an N-level system, with arbitrary Hamiltonian and bath spectral density, can be effectively emulated by an NMR system with log 2 N qubits.…”

“…[44][45][46][47][48][49][50][51] In 2012, Mostame et al 39 simulated a complicated environment with a given spectral density for the EET in photosynthetic complexes by using inductor-resistor-capacitor oscillators. In 2018, Potočnik et al 40,41 experimentally demonstrated that light harvesting for a given geometry can be optimized by tuning the environmental noise.…”