Single-molecule strong coupling at room temperature in plasmonic nanocavities


Photon emitters placed in an optical cavity experience an environment that changes how they are coupled to the surrounding light field. In the weak-coupling regime, the extraction of light from the emitter is enhanced. But more profound effects emerge when single-emitter strong coupling occurs: mixed states are produced that are part light, part matter1,2, forming building blocks for quantum information systems and for ultralow-power switches and lasers3,4,5,6. Such cavity quantum electrodynamics has until now been the preserve of low temperatures and complicated fabrication methods, compromising its use5,7,8. Here, by scaling the cavity volume to less than 40 cubic nanometres and using host–guest chemistry to align one to ten protectively isolated methylene-blue molecules, we reach the strong-coupling regime at room temperature and in ambient conditions. Dispersion curves from more than 50 such plasmonic nanocavities display characteristic light–matter mixing, with Rabi frequencies of 300 millielectronvolts for ten methylene-blue molecules, decreasing to 90 millielectronvolts for single molecules—matching quantitative models. Statistical analysis of vibrational spectroscopy time series and dark-field scattering spectra provides evidence of single-molecule strong coupling. This dressing of molecules with light can modify photochemistry, opening up the exploration of complex natural processes such as photosynthesis9 and the possibility of manipulating chemical bonds10.

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Figure 1: Comparing single-molecule optical cavities.
Figure 2: Plasmonic nanocavity containing a dye molecule.
Figure 3: Strong coupling seen in scattering spectra of individual NPoMs.
Figure 4: Rabi splitting from few molecules.


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We acknowledge financial support from the UK’s Engineering and Physical Sciences Research Council (grants EP/G060649/1, EP/N020669/1, EP/L027151/1 and EP/I012060/1) and the European Research Council (grant LINASS 320503). This study was partially supported by the Air Force Office of Scientific Research (AFOSR); the European Office of Aerospace Research and Development (EOARD) is also acknowledged. R.C. acknowledges support from the Dr. Manmohan Singh scholarship from St John’s College, University of Cambridge. F.B. acknowledges support from the Winton Programme for the Physics of Sustainability. S.J.B. acknowledges support from the European Commission for a Marie Curie Fellowship (NANOSPHERE, 658360).

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J.J.B. and R.C. conceived and designed the experiments. R.C. performed the experiments with input from F.B. and B.d.N. R.C. and A.D. carried out the simulation and the analytical modelling with input from J.J.B., P.F., O.H. and E.R. R.C. and J.J.B. analysed the data. S.J.B. and O.A.S. synthesized cucurbit[n]uril and provided input on the fabrication and characterization of samples. R.C. and J.J.B. wrote the manuscript with input from all authors.

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Correspondence to Jeremy J. Baumberg.

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The authors declare no competing financial interests.

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Chikkaraddy, R., de Nijs, B., Benz, F. et al. Single-molecule strong coupling at room temperature in plasmonic nanocavities. Nature 535, 127–130 (2016).

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