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Parity–time-symmetric whispering-gallery microcavities

Abstract

Optical systems combining balanced loss and gain provide a unique platform to implement classical analogues of quantum systems described by non-Hermitian parity–time (PT)-symmetric Hamiltonians. Such systems can be used to create synthetic materials with properties that cannot be attained in materials having only loss or only gain. Here we report PT-symmetry breaking in coupled optical resonators. We observed non-reciprocity in the PT-symmetry-breaking phase due to strong field localization, which significantly enhances nonlinearity. In the linear regime, light transmission is reciprocal regardless of whether the symmetry is broken or unbroken. We show that in one direction there is a complete absence of resonance peaks whereas in the other direction the transmission is resonantly enhanced, a feature directly associated with the use of resonant structures. Our results could lead to a new generation of synthetic optical systems enabling on-chip manipulation and control of light propagation.

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Figure 1: PT-symmetric whispering-gallery-mode microcavities.
Figure 2: PT-symmetry breaking in coupled WGM microresonators.
Figure 3: Input–output relation in PT-symmetric WGMRs and reciprocity in the linear regime.
Figure 4: Experimentally observed unidirectional transmission for PT-symmetric WGM microresonators in the nonlinear regime.

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Acknowledgements

This work is supported by Army Research Office grant No. W911NF-12-1-0026. C.M.B. is supported by US Department of Energy grant No. DE-FG02-91ER40628. F.N. is partially supported by the RIKEN iTHES Project, MURI Center for Dynamic Magneto-Optics, Grant-in-Aid for Scientific Research (S), MEXT Kakenhi on Quantum Cybernetics and the JSPS through its FIRST program. F.L. and G.L.L. are supported by the National Natural Science Foundation of China (Grant Nos 11175094, 91221205), the National Basic Research Program of China (Grant No. 2011CB921602), and the Collaborative Innovation Center of Quantum Matter, Beijing, China.

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S.K.O. and L.Y. conceived the idea and designed the experiments; B.P. performed the experiments with help from F.L., F.M. and S.K.O. Theoretical background and simulations were provided by F.L., F.M., M.G., C.M.B., S.F. and F.N. All authors discussed the results, and S.K.O. and L.Y. wrote the manuscript with inputs from all authors. L.Y. supervised the project.

Corresponding authors

Correspondence to Şahin Kaya Özdemir or Lan Yang.

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The authors declare no competing financial interests.

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Peng, B., Özdemir, Ş., Lei, F. et al. Parity–time-symmetric whispering-gallery microcavities. Nature Phys 10, 394–398 (2014). https://doi.org/10.1038/nphys2927

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