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# Optical parametric amplification by monolayer transition metal dichalcogenides

## Abstract

Optical parametric amplification is a second-order nonlinear process whereby an optical signal is amplified by a pump via the generation of an idler field1. This mechanism is inherently related to spontaneous parametric down-conversion, which currently constitutes the building block for entangled photon pair generation2, a process that is exploited in modern quantum technologies. Here we demonstrate single-pass optical parametric amplification at the ultimate thickness limit; using semiconducting transition metal dichalcogenides3,4, we show that amplification can be attained over propagation through a single atomic layer. Such a second-order nonlinear interaction at the two-dimensional limit bypasses phase-matching requirements5 and achieves ultrabroad amplification bandwidths. In agreement with first-principle calculations, we observe that the amplification process is independent of the in-plane polarization of signal and pump fields. By the use of AA-stacked multilayers, we present a clear pathway towards the scaling of conversion efficiency. Our results pave the way for the development of atom-sized tunable sources of radiation with potential applications in nanophotonics and quantum information technology.

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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 on reasonable request. Source data are provided with this paper.

## References

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## Acknowledgements

C.T., G.C., P.J.S., J.H. and N.C. acknowledge the project SONAR, which has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska–Curie grant agreement (no. 734690). G.C. acknowledges support by the European Union Horizon 2020 Programme under grant agreement no. 881603 Graphene Core 3. A.M. acknowledges support from the Rita Levi Montalcini Fellowship (grant no. PGR15PCCQ5) funded by the Italian Ministry of Education, Universities and Research (MIUR). A.C. acknowledges PRIN 2017 PELM (grant no. 20177PSCKT). X.Z. acknowledges support for the Vannevar Bush Faculty Fellowship through ONR grant N00014-18-1-2080 for sample preparation, and partial support by the National Science Foundation (NSF) grant DMR-1809680 for the development of the exfoliation technique. This research was supported in part by the Department of Energy (DOE) Office of Energy Efficiency and Renewable Energy (EERE) Postdoctoral Research Award under the EERE Solar Energy Technologies Office administered by the Oak Ridge Institute for Science and Education (ORISE) for the DOE. ORISE is managed by Oak Ridge Associated Universities (ORAU) under DOE contract no. DE-SC00014664. All opinions expressed in this paper are the author’s and do not necessarily reflect the policies and views of DOE, ORAU or ORISE. P.J.S., J.H. and K.Y. acknowledge support from Columbia University’s Fu Foundation School of Engineering and Applied Science Interdisciplinary Research Seed (SIRS) Funding program. Portions of this work are supported as part of Programmable Quantum Materials, an Energy Frontier Research Center funded by the US Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), under award DE-SC0019443.

## Author information

Authors

### Contributions

C.T. designed the experiment, built the set-up, performed the measurements and wrote the manuscript. A.M. performed the theoretical calculations and wrote the manuscript. X.X. and C.L. performed the measurements. F.L. and N.C. prepared the sample. C.M. designed the experiment and performed part of the theoretical calculations. A.C. performed part of the theoretical calculations. S.D.C. helped in the design of the experiment. J.H., X.Z., P.J.S. supervised the experiments and wrote the manuscript. G.C. designed and supervised the experiment, and wrote the manuscript.

### Corresponding authors

Correspondence to P. James Schuck or Giulio Cerullo.

## Ethics declarations

### Competing interests

The authors declare no competing interest.

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

## Supplementary information

### Supplementary Information

Supplementary Notes 1–8, Figs. 1–17 and References 1–8.

## Source data

### Source Data Fig. 1

Raw data and data fits from Fig. 1a–c.

### Source Data Fig. 2

Raw data and data fits from Fig. 2a–c.

### Source Data Fig. 3

Raw data from Fig. 3c.

## Rights and permissions

Reprints and Permissions

Trovatello, C., Marini, A., Xu, X. et al. Optical parametric amplification by monolayer transition metal dichalcogenides. Nat. Photonics 15, 6–10 (2021). https://doi.org/10.1038/s41566-020-00728-0

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• DOI: https://doi.org/10.1038/s41566-020-00728-0

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