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Turning a molecule into a coherent two-level quantum system


The use of molecules in quantum optical applications has been hampered by incoherent internal vibrations and other phononic interactions with their environment. Here we show that an organic molecule placed into an optical microcavity behaves as a coherent two-level quantum system. This allows the observation of 99% extinction of a laser beam by a single molecule, saturation with less than 0.5 photons and non-classical generation of few-photons super-bunched light. Furthermore, we demonstrate efficient interaction of the molecule–microcavity system with single photons generated by a second molecule in a distant laboratory. Our achievements represent an important step towards linear and nonlinear quantum photonic circuits based on organic platforms.

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Fig. 1: Schematics of the experimental arrangements.
Fig. 2: Resonant response of the molecule–microcavity composite to a laser beam.
Fig. 3: Frequency-detuned response of the molecule–cavity system.
Fig. 4: Large phase shift of a laser beam by a single molecule.
Fig. 5: Strong modification of photon statistics.
Fig. 6: Reflection of single photons.

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Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.


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The authors thank J. Renger, A. Dutschke and E. Butzen for the fabrication of micromirrors, M. Schwab for the construction of the mechanical components for the cryostats, and L. Meier for help with electronics to lock the cavity. This work was supported by the Max Planck Society.

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Authors and Affiliations



D.W. and H.K. performed the cavity experiments and analysed the data. D.R. and A.S. were responsible for the generation of single photons. T.U., S.G. and V.S. supervised the experiments. D.M.-C. contributed to theoretical analysis of the system. The manuscript was written by V.S. and all authors commented on it.

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Correspondence to Vahid Sandoghdar.

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The authors declare no competing interests.

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Journal peer review information: Nature Physics thanks Girish Agarwal, Barak Dayan and the other anonymous reviewer(s) for their contribution to the peer review of this work.

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Wang, D., Kelkar, H., Martin-Cano, D. et al. Turning a molecule into a coherent two-level quantum system. Nat. Phys. 15, 483–489 (2019).

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