Suchergebnisse

Molecular emitters located in an optical cavity are known to experience a dramatic modification of the energy and dynamics of their light emission, establishing novel routes for the generation of non-classical states of light. Under monochromatic illumination, spectral asymmetries in cavity-enhanced molecular fluorescence often emerge due to the formation of hybrid polaritonic states (upper and lower polaritons). By applying the theory of open-quantum systems, we show that under strong-coupling conditions, it is essential to account for the interaction of the molecular electronic states with their vibrational environment (dephasing reservoir) to address the complex dynamics of light emission. The interaction with the dephasing reservoir yields a transfer of energy between the polariton states, favoring the transition toward the lower polariton. As a result, we show that the inelastic light emission originates mainly from the lower polariton state regardless of the pumping laser frequency, thus producing asymmetric light emission spectra. Furthermore, we show that, when several molecules are considered, intermolecular coupling can break the symmetry of the system, enabling originally dark polaritons to emit light, as revealed in the fluorescence spectrum by the emergence of new emission peaks. These results stress that accounting for the interaction with dephasing reservoirs is key to interpret molecular light emission in cavities, consistent with experimental observations. ; Spanish Ministry of Science, Innovation and Universities (MICIN) (FIS2016-80174-P); Physical Measurement Laboratory (PML) of NIST (70NANB15H32); Department of Education of the Basque Government (IT-756-13). ; Peer reviewed

Localised surface plasmons can couple strongly with the electronic transitions of a molecule, inducing new hybridised states of light and matter, the plasmon–exciton polaritons. Furthermore, molecules support vibrational degrees of freedom that interact with the electronic levels, giving rise to inelastic resonant Raman scattering under coherent laser illumination. Here we show the influence of strong plasmon–exciton coupling on resonant Raman processes that populate the vibrational states of the molecule and that lead to the characteristic surface-enhanced Raman scattering spectra. We develop analytical expressions that give insight into these processes for the case of moderate illumination intensity, weak electron–vibration coupling and no dephasing. These expressions help us to elucidate the twofold role of plasmon–exciton polaritons to pump the system efficiently and to enhance the Raman emission. Our results show a close analogy with the optomechanical process described for off-resonant Raman scattering but with a difference in the resonant reservoir. We also use full numerical calculations to study the effects reaching beyond these approximations and discuss the interplay between the fluorescence background and the Raman lines. Our results allow for better understanding and exploitation of the strong coupling regime in vibrational pumping and in the surface-enhanced resonant Raman scattering signal. ; The authors acknowledge project FIS2016-80174-P from the Spanish Ministry of Education, H2020-FETOPEN project "THOR" Nr. 829067 from the European Commission, grant IT1164-19 for consolidated groups of the University from the Basque Government, and project PI2017-30 of the Departamento de Educación, Política Lingüística y Cultura of the Basque Government. ; Peer reviewed

Plasmonic cavities can confine electromagnetic radiation to deep sub-wavelength regimes. This facilitates strong coupling phenomena to be observed at the limit of individual quantum emitters. Here, we report an extensive set of measurements of plasmonic cavities hosting one to a few semiconductor quantum dots. Scattering spectra show Rabi splitting, demonstrating that these devices are close to the strong coupling regime. Using Hanbury Brown and Twiss interferometry, we observe non-classical emission, allowing us to directly determine the number of emitters in each device. Surprising features in photoluminescence spectra point to the contribution of multiple excited states. Using model simulations based on an extended Jaynes-Cummings Hamiltonian, we find that the involvement of a dark state of the quantum dots explains the experimental findings. The coupling of quantum emitters to plasmonic cavities thus exposes complex relaxation pathways and emerges as an unconventional means to control dynamics of quantum states. ; S.N.G. thanks the Government of Israel for a Planning and Budgeting Committee Fellowship. G.H. is the incumbent of the Hilda Pomeraniec Memorial Professorial Chair. R.E., T.N. and J.A. acknowledge funding from projects FIS2016-80174-P and PID2019-107432GB-I00 of the Spanish Ministry of Science, Innovation and Universities MICINN, as well as funding from grant IT1164-19 for consolidated groups of the Basque University, through the Department of Universities of the Basque Government. This project received partial support from the European Union's Horizon 2020 research and innovation programme under grant agreement no. 861950, project POSEIDON, and grant agreement no. 810626, project SINNCE. ; Peer reviewed