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Nanoplasmonic (meta-)materials and nanophotonics have the unique ability to confine light in extremely sub-wavelength volumes and thereby strongly enhance the effective strength of electromagnetic fields. Fundamentally, such high-field enhancement can alter the local density of states experienced by a photoactive molecule to unprecedented degrees and control its exchange of energy with light. For a sufficiently strong field enhancement, one enters the strong-coupling regime, where the energy exchange between the excited states of molecules/materials and plasmons is faster than the de-coherence processes of the system. As a result, the excitonic state of the molecule becomes entangled with the photonic mode, forming hybrid excitonic-photonic states. These hybrid-states are part light, part matter and allow for characteristic Rabi oscillations of atomic excitations to be observed. Until recently, the conditions for achieving strong-coupling were most commonly met at low temperatures, where de-coherence processes are suppressed. As a major step forward, we have recently demonstrated room-temperature strong coupling of single molecules in a plasmonic nano-cavity [1] which was achieved using a host-guest chemistry technique, controlling matter at the molecular level. Concurrently, linking nano-spectroscopy of quantum dots with strong coupling allows to lithographically realise a strong-coupling set-up that couples dark plasmonic modes and quantum dots [2]. Remarkably, through strong coupling we obtain spectroscopic access to otherwise veiled states (such as the charged trion state) enabled through a strong-coupling induced speed up of the radiative dynamics of the quantum dot states [3]. Considering the key importance of strong coupling in quantum optics our findings pave the road for a wide range of ultrafast quantum optics experiments and quantum technologies at ambient conditions. Moreover, the pronounced position-dependent spectral changes may lead to new types of quantum sensors and near-field quantum imaging modalities. Finally we shall consider strong coupling in hyperbolic metamaterials.
References
[1] R. Chikkaraddy, B. de Nijs, F. Benz, S. J. Barrow, O. A. Sherman, E. Rosta, A. Demetriadou, P. Fox, O. Hess and J. J. Baumberg, Nature 535, 127 (2016).
[2] N Kongsuwan, A Demetriadou, R. Chikkaraddy, F. Benz, V. A. Turek, U. F. Keyser, J. J. Baumberg and O. Hess, ACS Photonics 5, 186 (2017)
[3] H. Gross, J. M. Hamm, T. Tuffarelli, O. Hess and B. Hecht, Science Advances 4, eaar4906 (2018).
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