Molecular photons interfaced with alkali atoms


Future quantum communication will rely on the integration of single-photon sources, quantum memories and systems with strong single-photon nonlinearities1. Two key parameters are crucial for the single-photon source: a high photon flux with a very small bandwidth, and a spectral match to other components of the system. Atoms or ions may act as single-photon sources—owing to their narrowband emission and their intrinsic spectral match to other atomic systems—and can serve as quantum nonlinear elements. Unfortunately, their emission rates are still limited, even for highly efficient cavity designs2. Single solid-state emitters such as single organic dye molecules are significantly brighter3 and allow for narrowband photons4; they have shown potential in a variety of quantum optical experiments5,6 but have yet to be interfaced with other components such as stationary memory qubits. Here we describe the optical interaction between Fourier-limited photons from a single organic molecule and atomic alkali vapours, which can constitute an efficient quantum memory. Single-photon emission rates reach up to several hundred thousand counts per second and show a high spectral brightness of 30,000 detectable photons per second per megahertz of bandwidth. The molecular emission is robust and we demonstrate perfect tuning to the spectral transitions of the sodium D line and efficient filtering, even for emitters at ambient conditions. In addition, we achieve storage of molecular photons originating from a single dibenzanthanthrene molecule in atomic sodium vapour. Given the large set of molecular emission lines matching to atomic transitions, our results enable the combination of almost ideal single-photon sources with various atomic vapours, such that experiments with giant single-photon nonlinearities, mediated, for example, by Rydberg atoms7,8, become feasible.

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Figure 1: Spectral match of DBATT to atomic sodium.
Figure 2: Spectroscopy and microscopy of molecules and atoms.
Figure 3: Narrow-band filtering of the molecular emission by atomic vapour.
Figure 4: Near-sodium-resonance photons.


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We thank W. Kiefer for the calculation of the sodium-2-FADOF transmission (Fig. 3). G.S. acknowledges support by J. Pflaum (University of Würzburg). I.G. acknowledges discussions with R. Löw and S. Hofferberth (University of Stuttgart). J.W. acknowledges support by the Max Planck Society (via a Max Planck fellowship), the BMBF (via the projects QuORep and and the EU (via the project SIQS and the ERC grant SQUTEC).

Author information

I.G. conceived the idea. P.S., G.S. and I.G. prepared and conducted the experiments. I.G. and J.W. supervised the team and wrote the manuscript.

Correspondence to Ilja Gerhardt.

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The authors declare no competing financial interests.

Extended data figures and tables

Extended Data Figure 1 Imaging fluorescent samples, supported by atomic vapour.

Single fluorescent bead, imaged in a confocal microscope, illuminated with laser light, locked to the crossover resonance of the sodium D2 transition. Although the overall count rate does not substantially differ, the signal-to-noise ratio is measured to be 210 when using the commercial filter, and 240 when only the sodium filter is used. Integration time per pixel is 2 ms.

Extended Data Figure 2 Combined spectroscopy of DBT and potassium.

Spectra of single DBT molecules and atomic K vapour on the K D2 line around 766 nm. The molecules in the sample are sparse. Therefore, the image represents multiple recordings at several lateral positions.

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Siyushev, P., Stein, G., Wrachtrup, J. et al. Molecular photons interfaced with alkali atoms. Nature 509, 66–70 (2014).

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