2D Materials: A New Platform to Realize “Quantum Light-Matter”

Atomically thin materials, such as graphene and transitional metal dichalcogenides (TMDs), have recently come to the forefront of research in materials physics. This is largely due to the ease with which they can be combined into artificially engineered heterostructures that exhibit emergent electronic and optical properties. Enhanced Coulomb interactions in the truly 2D limit and flat bands in TMD moiré heterostructures, such as MoSe₂/WSe₂, provide a rich platform to explore correlated quantum phases of matter. Moreover, the same interactions also lead to very strong light-matter couplings, resulting in rich exciton physics and half-light, half-matter polaritonic states. Finally, the presence of non-trivial geometry and topology¹ in electronic and optical states of these materials is an additional ingredient to realize coupled phases of quantum light and matter– quantum light-matter – that are not only interesting from a fundamental perspective but can also have applications in quantum information processing applications.

In this talk, I will begin by highlighting some unique properties of optical excitations in TMDs which result from the chiral nature of constituent single-particle electronic states. Next, I will talk about quantum emitters in monolayer TMDs with valley pseudo-spin degree of freedom which can be optically initialized^2,3. I will also present evidence for an intriguing quantum entanglement between chiral phonons of the 2D host and single photons emitted from the quantum dots⁴. Unlike their monolayer counterparts, quantum emitters in heterobilayers feature a permanent electric dipole which can be used to tune their emission energy electrically and also induce quantum non-linearity through dipolar interactions⁵. Finally, I will present our recent results wherein many-exciton dipolar interactions result in exchange fields of ~ 6 Tesla⁶. I will conclude by discussing the outlook for realizing strongly interacting phases of optical excitations in 2D materials.

1. A. Srivastava et al., Nature Nanotechnology. 10, 491-496 (2015)
2. A. Srivastava and Ataç Imamoglu Phys. Rev. Lett. 115, 166802 (2015)
3. X. Lu, X. Chen, S. Dubey et al., Nature Nanotechnology. 14, 426-431 (2019)
4. X. Chen, X. Lu, S. Dubey et al., Nature Physics. 15, 221-227 (2019)
5. W. Li, X. Lu et al., Nature Materials. 19, 624-629 (2020)
6. W. Li, X. Lu et al., Nature Nanotechnology 16, 148-152 (2021).