Steady-state Fano coherences in a V-type system driven by polarized incoherent light

Amro Dodin,Suyesh Koyu,Paul Brumer,Timur V Tscherbul

doi:10.1103/physrevresearch.3.013295

Amro Dodin, Suyesh Koyu + Show 2 more

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https://doi.org/10.1103/physrevresearch.3.013295

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Abstract

We explore the properties of steady-state Fano coherences generated in a three-level V-system continuously pumped by polarized incoherent light in the absence of coherent driving. The ratio of the stationary coherences to excited-state populations $\mathcal{C} = (1+\frac{\Delta^2}{\gamma(r+\gamma)} )^{-1}$ is maximized when the excited-state splitting $\Delta$ is small compared to either the spontaneous decay rate $\gamma$ or the incoherent pumping rate $r$. We demonstrate that an intriguing regime exists where the $\mathcal{C}$ ratio displays a maximum as a function of the dephasing rate $\gamma_d$. We attribute the surprising dephasing-induced enhancement of stationary Fano coherences to the environmental suppression of destructive interference of individual incoherent excitations generated at different times. We identify the imaginary Fano coherence with the non-equilibrium flux across a pair of qubits coupled to two independent thermal baths, unraveling a direct connection between the seemingly unrelated phenomena of incoherent driving of multilevel quantum systems and non-equilibrium quantum transport in qubit networks. The real part of the steady-state Fano coherence is found to be proportional to the deviation of excited-state populations from their values in thermodynamic equilibrium, making it possible to observe signatures of steady-state Fano coherences in excited-state populations. We put forward an experimental proposal for observing steady-state Fano coherences by detecting the total fluorescence signal emitted by Calcium atoms excited by polarized vs. isotropic incoherent light. Our analysis paves the way toward further theoretical and experimental studies of non-equilibrium coherent steady states in thermally driven atomic and molecular systems, and for the exploration of their potential role in biological processes.

Highlights

Quantum coherence is widely regarded as an essential resource [1] for quantum information processing [2], quantum sensing [3], and quantum interferometry [4]
We have presented closed-form analytical solutions to the BR quantum master equations for a three-level V-system driven by polarized incoherent radiation, which reveal the presence of nonequilibrium steady states (NESS) featuring substantial Fano coherences in the energy eigenstate basis
The rates of isotropic incoherent pumping r and spontaneous emission γ are balanced, i.e., related by the equilibrium fluctuation-dissipation theorem r = nγ, and no steady-state Fano coherences survive in the V-system driven by unpolarized incoherent light [27]

Summary

Introduction

Quantum coherence is widely regarded as an essential resource [1] for quantum information processing [2], quantum sensing [3], and quantum interferometry [4]. An additional motivation to study decoherence comes from recent experimental and theoretical studies of quantum effects in biological processes, such as photosynthetic energy transfer [6,7,8], vision [9,10], and avian magnetoreception [11]. These studies have indicated that nontrivial quantum effects such as coherence and entanglement [6,7] can persist under noisy conditions typical of biological environments at room temperature. Biologically relevant photosynthetic light-harvesting is driven by natural sunlight, which is an incoherent mixture of number states, raising an important question: can excitation by incoherent light alone (i.e., in the absence of coherent laser driving) generate coherence in multilevel quantum systems [8,12,13,14,15,16,17,18]

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