Topological insulators have been a fascinating mainstay of condensed matter physics for the past four decades, since the deep connections were established between the physics of the quantum Hall effect and the mathematics of topoly – which concerns itself with the study of geometric objects under continuous deformations. Topological insulators are unique in that they are conducting at the edge but insulating in their bulk, and the number of such conduction channels is related by the bulk-edge correspondence to an integer topological invariant of the bulk band structure. These conduction channels are remarkably robust against backscattering by disorder, which leads to them being called one-way chiral edge states.

The past decade has witnessed the rapid growth of photonic analogues of topological insulators, not only to demonstrate similar fundamental physics effects, but also to use them for robust light guiding, lasing and isolation. Even more recently, synthetic dimensions have provided novel alternatives to probe these physical phenomena in simpler structures. Examples of the wide variety of physics studied include the integer quantum Hall effect, artificial magnetic fields, spin-orbit coupling, spin-momentum locking, and topological one-way edge states at optical frequencies, observed at room temperature.

An exciting aspect of photonics, especially in synthetic dimensions, is that non-Hermitian Hamiltonians can be readily implemented. Such non-Hermitian models host unique phenomena such as the non-Hermitian skin effect with no Hermitian analogues, and are very difficult to realize in condensed matter physics. This is a prime example of what photonics brings to the table in terms of new physics beyond building analogues of what was predicted in the initial domains of topology – the physics of electrons in condensed matter.

We are interested in building very high-dimensional topological photonic systems using a combination of real-space and synthetic-space techniques, and exploring exotic light-matter phases as well as applications that arise from the rich interplay between topology, dimensionality, nonlinearity, and non-Hermiticity.

Video of experimental band structure spectroscopy, A. Dutt, M. Minkov, Q. Lin, L. Yuan, D. A. B. Miller, S. Fan, Nature Communications (2019).

Tutorials and reviews

• H. Price, Y. Chong, A. Khanikaev, … A. Dutt, …, et al., “Roadmap on topological photonics,” J. Phys. Photonics (2022).
• L. Lu, J. D. Joannopoulos, and M. Soljačić, “Topological photonics,” Nature Photonics 8, 821 (2014).
• L. Yuan, A. Dutt, and S. Fan, “Synthetic frequency dimensions in dynamically modulated ring resonators,” APL Photonics 6, 071102 (2021).
• L. Yuan, Q. Lin, M. Xiao, and S. Fan, “Synthetic dimension in photonics,” Optica 5, 1396–1405 (2018).

Original research papers from our work

• A. Dutt, Q. Lin, L. Yuan, M. Minkov, M. Xiao, and S. Fan, “A single photonic cavity with two independent physical synthetic dimensions,” Science 367, 59 (2020). [Quantum Hall effects]
• K. Wang*, A. Dutt*, K. Y. Yang, C. C. Wojcik, J. Vučković, and S. Fan, “Generating arbitrary topological windings of a non-Hermitian band,” Science 371, 1240 (2021). [Non-Hermitian physics]
• K. Wang, A. Dutt, C. C. Wojcik, and S. Fan, “Topological complex-energy braiding of non-Hermitian bands,” Nature 598, 59 (2021). [Non-Hermitian physics]
• C. Leefmans*, A. Dutt*, J. Williams, L. Yuan, M. Parto, F. Nori, S. Fan, and A. Marandi, “Topological Dissipation in a Time-Multiplexed Photonic Resonator Network,” arXiv:2104.05213 (2021). [Driven-dissipative models]
• A. Dutt, M. Minkov, I.A.D. Williamson, S. Fan, “Higher-order topological insulators in synthetic dimensions,” Light: Science & Applications 9, 131 (2020). [higher-order topology]
• A. Dutt, M. Minkov, Q. Lin, L. Yuan, D. A. B. Miller, S. Fan, “Experimental band structure spectroscopy along a synthetic dimension,” Nature Communications 10, 3122 (2019).
• J. Zhong, K. Wang, Y. Park, V. Asadchy, C. C. Wojcik, A. Dutt, and S. Fan, “Nontrivial point-gap topology and non-Hermitian skin effect in photonic crystals,” Phys. Rev. B 104, 125416 (2021). [photonic crystals, non-Hermitian physics]
• A. Y. Song, X.-Q. Sun, A. Dutt, M. Minkov, C. Wojcik, H. Wang, I.A.D. Williamson, M. Orenstein, S. Fan, “PT-symmetric topological edge-gain effect,” Phys. Rev. Lett. 125, 033603 (2020). [Non-Hermitian physics]
• L. Yuan, Q. Lin, M. Xiao, A. Dutt, S. Fan, “Pulse shortening in an actively mode-locked laser with parity-time symmetry,” APL Photonics 3, 086103 (2018). [Non-Hermitian physics, lasers and mode-locking]