Collective strong coupling of X-rays and nuclei in a nuclear optical lattice


The advent of third-generation synchrotron radiation sources and X-ray free-electron lasers has opened up the opportunity to perform quantum optical experiments with high-energy X-rays. The prime atomic system for experiments in this energy range is the strongly nuclear resonant 57Fe Mössbauer isotope. Experiments have included measurements of the collective Lamb shift1, observation of electromagnetically induced transparency2, subluminal propagation of X-rays3,6 and spontaneously generated coherences4,5,7. In these experiments, however, the nuclei were only weakly coupled to the light field. Collective strong coupling of nuclei and X-rays, which is desirable for many quantum optical applications, has eluded researchers so far. Here, we observe collective strong coupling between X-rays and matter excitations in a periodic array of alternating 57Fe and 56Fe layers. Our experiment extends the range of methods for X-ray quantum optics and paves the way for the observation and exploitation of strong-coupling-related phenomena at X-ray energies.

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Figure 1: Experimental set-up.
Figure 2: Angular-dependent dispersion relation.
Figure 3: Dispersion relation of an infinite array of 57Fe nuclei arranged in a bichromatic lattice.
Figure 4: Calculated multilayer reflectivity.
Figure 5: Measured energy spectra of the multilayer reflectivity.


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The authors thank D. Schumacher for discussions and assistance during the experiment, and J. Evers and K. Heeg for discussions. The authors acknowledge support from the Bundesministerium für Bildung und Forschung (project no. 05K13SJ1).

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R.R. conceived the experiment and coordinated the experimental efforts. K.S.S., R.L., H.B., I.U. and G.G.P. developed the polarimetry set-up. T.G. fabricated the sample. K.S.S., R.L., J.H., L.B., K.S., H.-C.W., H.B., I.U., R.R. and R.R. participated in performing the experiment. J.H. developed the theoretical interpretation and performed the data analysis. J.H. and R.R. wrote the manuscript. All authors participated in discussing the results.

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Correspondence to Ralf Röhlsberger.

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Haber, J., Schulze, K., Schlage, K. et al. Collective strong coupling of X-rays and nuclei in a nuclear optical lattice. Nature Photon 10, 445–449 (2016).

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