Dynamics of Strongly Coupled Hybrid States by Transient Absorption Spectroscopy

Abstract

Since the birth of quantum mechanics the construction and control of novel hybrid quantum states are among the dream targets of scientists. In this regard, due to recent technological advances, hybrid states based on strong coupling occurring between light and matter have become a laboratory reality. For example, it is demonstrated that strong coupling involving microcavities or surface plasmon polaritons shows great potential for novel nanoplasmonic devices such as lasers, all-optical switching, field-effect transistors, and for the evergreen field of quantum computation. Further developments in this field require, however, a better understanding of the underlying mechanisms governing strong coupling, especially from a time-dependent point of view, time-resolved spectroscopy being one of the leading experimental approaches to address this aspect. In this perspective, after a brief introduction of the strong coupling concept, the recent research progress on the dynamics of strongly coupled systems involving J-aggregates, broadly absorptive dyes, semiconductor quantum dots, and perovskite films with either microcavities or surface plasmons polaritons is summarized and discussed. Finally, challenges and perspectives for developing strong coupling concept are further illustrated, with special attention to phonon-photon interaction, as one of the most intriguing topics in condensed matter physics.

Polariton Formation from Soret Band Excitons in Metal–Organic Frameworks and Plasmonic Lattices

“…Although the UP was not visible in the steady-state optical measurements, the sensitivity of TA can reveal this feature, and polariton modes have been well-reported in TA measurements. 7 Additionally, the polariton modes are in good agreement with the values predicted from the Jaynes−Cummings model (λ = 450 and 400 nm for LP and UP, respectively). The splitting between the UP and LP bleach signals is 324 meV, which is well above previously reported Rabi splitting for SLR-exciton strong coupling.…”

“…The spectra at n = 1.29 reveals a UP bleach (λ = 413 nm), LP bleach (λ = 463 nm), and another feature at the same wavelength as the uncoupled Soret band (λ = 440 nm). Although the UP was not visible in the steady-state optical measurements, the sensitivity of TA can reveal this feature, and polariton modes have been well-reported in TA measurements . Additionally, the polariton modes are in good agreement with the values predicted from the Jaynes–Cummings model (λ = 450 and 400 nm for LP and UP, respectively).…”

Energy relaxation pathways between light-matter states revealed by coherent two-dimensional spectroscopy

“…This observation is rationalised by the relatively narrow energy distribution of the dark J-aggregate states and the large energy gap between P − and J. The long-lived nature of P − corresponds well to the observation that strong coupling can lead to the emergence of quasi-bound polaritonic states 20,43,45 . DelPo et al report on strongly coupled charge-transfer transitions in 4CzIPN…”

Ultrafast Dynamics of Multiple Plexcitons in Colloidal Nanomaterials: The Mediating Action of Plasmon Resonances and Dark States

“…In addition to negative GSB signals, strong positive ESA signals are recorded at ∼500 and 630 nm. They can be associated with each GSB signal to form a sort of derivative-like band shape, as typically found for polaritonic systems. ,,− Derivative-like features are typically associated with a “contraction” of the Rabi splitting after photoexcitation, which reduces the density of molecules in the ground state able to participate in plexciton formation. , In this case, the Rabi splitting is dependent on the pump intensity, and a time-dependent Rabi contraction is measured in TA spectra. ,, Since in our experimental conditions we did not observe any significant shift of the plexciton peaks, we attribute these features as originating from the excited-state absorption from the “one-particle” plexcitons and/or the dark states to higher-energy “two-particle” states. , Dark states are formed in the nanohybrid as a consequence of the various symmetry of the interactions between a large number of molecules and the plasmon mode, resulting not only in the hybrid plexcitons but also in a large number of purely molecular dark states located at the energy of the bare molecules. ,, Dark states get readily populated from higher energy states in time scales less than 100 fs, and, because of their high density, they can efficiently act as a sink of excitation from plexcitons, affecting in a significant way the overall dynamics of nanohybrids, as will be discussed later. − ,, Indeed, energy transfer between polaritons and dark states manifold has been often proposed as a possible mechanism to justify long polariton lifetimes in microcavities. , …”