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Quantum interference in second-harmonic generation from monolayer WSe2


A hallmark of wave–matter duality is the emergence of quantum-interference phenomena when an electronic transition follows different trajectories. This type of interference results in asymmetric absorption lines such as Fano resonances1, and gives rise to secondary effects such as electromagnetically induced transparency when multiple optical transitions are pumped2,3,4,5. Few solid-state systems show quantum interference and electromagnetically induced transparency5,6,7,8,9,10,11, with quantum-well intersubband transitions in the infrared region12,13 offering the most promising avenue to date to devices exploiting optical gain without inversion14,15. Quantum interference is usually hampered by inhomogeneous broadening of electronic transitions, making it challenging to achieve in solids at visible wavelengths and elevated temperatures. However, disorder effects can be mitigated by raising the oscillator strength of atom-like electronic transitions—excitons—that arise in monolayers of transition-metal dichalcogenides16,17. Quantum interference, probed by second-harmonic generation18,19, emerges in monolayer WSe2, without a cavity, to split the frequency-doubled laser spectrum. The splitting exhibits spectral anticrossing behaviour, and is related to the number of Rabi flops the strongly driven system undergoes. The second-harmonic generation power-law exponent deviates strongly from the canonical value of 2, showing a Fano-like wavelength dependence that is retained at room temperature. The work opens opportunities in solid-state quantum-nonlinear optics for optical mixing, gain without inversion and quantum-information processing.

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Fig. 1: Quantum interference in the SHG of single-layer WSe2 at 5 K.
Fig. 2: Correspondence between Rabi flopping of the strongly driven system and SHG splitting.
Fig. 3: Experimental temperature dependence of quantum interference in SHG from hBN-encapsulated monolayer WSe2.
Fig. 4: Dependence of the SHG power-law exponent on the excitation and emission wavelength.

Data availability

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


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The authors thank A. Chernikov, R. Huber, T. Korn, F. Langer, P. Nagler, A. Kormányos and B. Ren for helpful discussions, S. Krug for technical support, and R. Martin for assistance with sample preparation. Financial support is gratefully acknowledged from the German Science Foundation through SFB 1277 project B03.

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Authors and Affiliations



K.-Q.L. conceived and performed the experiments with the support of S.B. S.B. wrote the simulation codes and carried out simulations with K.-Q.L. K.-Q.L., S.B. and J.M.L. analysed the data and wrote the paper.

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Correspondence to Kai-Qiang Lin or John M. Lupton.

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Lin, KQ., Bange, S. & Lupton, J.M. Quantum interference in second-harmonic generation from monolayer WSe2. Nat. Phys. 15, 242–246 (2019).

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