Strain Engineering of Proximity Interaction for Controlling Polarization of Quantum Light Emitters

An ability to control the polarization of the single photons generated by the quantum light emitters holds the key to the realization of non-reciprocal single-photon devices, deterministic spin-photon interfaces, and complex quantum networks. To date, such control is usually achieved via coupling of the quantum emitters to the complex photonic/meta-structures. Achieving circularly polarized light emission is significantly more difficult than achieving linearly polarized light emission as it often requires more sophisticated structures, injection of spin-polarized carriers/excitons, or application of high magnetic fields. “Proximity effects” – the class of phenomena by which an atomically-thin material borrows properties of an adjacent material (such as magnetism) via quantum mechanical interactions – has recently been explored to achieve this highly desired polarization control. By coupling transition metal dichalcogenides with various bulk and 2D magnetic materials, exciting effects such as strong enhancement of valley Zeeman splitting and spin-dependent charge transfer have been demonstrated. However, chiral light emission without spin-polarized carrier/exciton injection at zero magnetic field remains elusive to date. Here in this talk, we will first demonstrate that chiral quantum light sources with a high degree of circular polarization (&gt;0.9) and 80% single-photon purity <i>can</i> be realized by strain-engineering the WSe₂\NiPS₃ heterostructures with nanoscale indentations. Through state of art scanning diamond NV microscopy experiments and temperature-dependent magneto-photoluminescence studies, we show that the chiral quantum light emission arises from magnetic proximity interactions between localized excitons in the WSe₂ monolayer and out-of-plane magnetization of AFM defects in NiPS₃, both of which are co-localized by the strain field arising from the nanoscale indentations. Interestingly, a similar chiral localized excitonic emission is also observed in our more recent experiment performed on WSe₂/MnPS₃ and WSe₂/FePS₃ heterostructure with nano-indents. Furthermore, we demonstrated that the application of the same strain engineering approach (i.e nanoindentation) to WSe₂/CrPS₄ heterostructure lead to the emission of linearly polarized quantum light reflecting the magnetic order of CrPS₄. These observations reveal that local strain engineering can be utilized not only to create quantum emitters but also to manipulate local proximity interaction for control of their PL polarization.