[Paper Review] Plasmon mediated coherent population oscillations in molecular aggregates

Daniel Timmer, Moritz Gittinger+10 more|arXiv (Cornell University)|Jul 27, 2023

Spectroscopy and Quantum Chemical StudiesPhysics and Astronomy58 references3 citations

TL;DR

This study demonstrates room-temperature coherent population oscillations in J-aggregate excitons strongly coupled to plasmonic fields in a gold nanoslit array, using ultrafast two-dimensional electronic spectroscopy. The results reveal plasmon-mediated coherent exciton transport over mesoscopic distances, enabling control of quantum dynamics via vacuum field coupling despite ambient decoherence.

ABSTRACT

The strong coherent coupling of quantum emitters to vacuum fluctuations of the light field offers opportunities for manipulating the optical and transport properties of nanomaterials, with potential applications ranging from ultrasensitive all-optical switching to creating polariton condensates. Often, ubiquitous decoherence processes at ambient conditions limit these couplings to such short time scales that the quantum dynamics of the interacting system remains elusive. Prominent examples are strongly coupled exciton-plasmon systems, which, so far, have mostly been investigated by linear optical spectroscopy. Here, we use ultrafast two-dimensional electronic spectroscopy to probe the quantum dynamics of J-aggregate excitons collectively coupled to the spatially structured plasmonic fields of a gold nanoslit array. We observe rich coherent Rabi oscillation dynamics reflecting a plasmon-driven coherent exciton population transfer over mesoscopic distances at room temperature. This opens up new opportunities to manipulate the coherent transport of matter excitations by coupling to vacuum fields.

Motivation & Objective

• To investigate coherent quantum dynamics in molecular aggregates strongly coupled to plasmonic fields under ambient conditions.
• To overcome the challenge of decoherence limiting coherent phenomena in nanomaterials at room temperature.
• To explore the role of spatially structured plasmonic fields in mediating coherent population transfer in excitonic systems.
• To demonstrate coherent transport of matter excitations over mesoscopic distances via vacuum field coupling.
• To advance the understanding of exciton-plasmon interactions for applications in quantum control and nanophotonic devices.

Proposed method

• Employed ultrafast two-dimensional electronic spectroscopy to probe coherent quantum dynamics in J-aggregate excitons.
• Used a gold nanoslit array to generate spatially structured plasmonic fields that couple strongly to excitons.
• Measured coherent Rabi oscillations in the electronic response to infer population transfer dynamics.
• Analyzed the time-resolved spectral signals to extract coherence lifetimes and coupling strengths.
• Compared experimental data with theoretical models of exciton-plasmon coupling in open quantum systems.
• Focused on room-temperature operation to assess feasibility for practical nanophotonic applications.

Experimental results

Research questions

• RQ1 Can coherent population oscillations be observed in molecular aggregates coupled to plasmonic fields at room temperature?
• RQ2 To what extent do plasmonic fields mediate coherent exciton transport over mesoscopic distances?
• RQ3 How does the spatial structure of the plasmonic field influence the coherence and dynamics of excitonic populations?
• RQ4 What is the role of vacuum field coupling in sustaining coherent dynamics despite ambient decoherence?
• RQ5 Can ultrafast 2D spectroscopy resolve the interplay between plasmon-enhanced coupling and decoherence in excitonic systems?

Key findings

• Coherent Rabi oscillations in J-aggregate excitons were observed at room temperature, indicating long-lived quantum coherence.
• Plasmonic fields in the gold nanoslit array mediated coherent population transfer over mesoscopic distances (on the order of micrometers).
• The oscillation frequency and decay dynamics revealed strong coupling between excitons and plasmonic modes.
• The system exhibited coherent dynamics persisting beyond typical decoherence times, attributed to plasmon-mediated protection.
• Ultrafast 2D spectroscopy resolved the interplay between coherent population transfer and dephasing processes.
• The results demonstrate that plasmonic fields can sustain and control coherent quantum transport in molecular aggregates under ambient conditions.