ABSTRACT
Spin angular momentum (SAM)-encoded single-photon emitters, also known as circularly polarized single photons, are basic building blocks for the advancement of chiral quantum optics and cryptography. Despite substantial efforts such as coupling quantum emitters to grating-like optical metasurfaces and applying intense magnetic fields, it remains challenging to generate circularly polarized single photons from a subwavelength-scale nanostructure in the absence of a magnetic field. Here, we demonstrate single-photon emitters encoded with SAM in a strained WSe2 monolayer coupled with chiral plasmonic gold nanoparticles. Single-photon emissions were observed at the nanoparticle position, exhibiting photon antibunching behavior with a g(2)(0) value of ~0.3 and circular polarization properties with a slight preference for left-circular polarization. Specifically, the measured Stokes parameters confirmed strong circular polarization characteristics, in contrast to emitters coupled with achiral gold nanocubes. Therefore, this work provides potential insights to make SAM-encoded single-photon emitters and understand the interaction of plasmonic dipoles and single photons, facilitating the development of chiral quantum optics.
ABSTRACT
Transition metal dichalcogenides (TMDs) are actively studied in various fields of optics and optoelectronics, including nonlinear optics of second-harmonic generation (SHG). By stacking two different TMD materials to form a heterobilyaer, unique optical properties emerge, with stronger SHG at a twist angle of 0° between TMDs and weaker SHG at a twist angle of 60°. In this work, we demonstrate the enhancement of SHG in a heterobilayer consisting of WSe2and WS2monolayers stacked at a twist angle of 64.1°, using a nanoparticle to induce local strain. The interatomic spacing of the heterobilayer is deformed by the nanoparticle, breaking the inversion symmetry, resulting in a substantial increase in the SHG of the heterobilayer at room temperature. The SHG increases depending on the polarization of the pump laser: 15-fold for linear polarization, 9-fold for right-circular polarization, and up to 100-fold for left-circular polarization. In addition, the SHG enhanced in the heterobilayer with local strain satisfies the same chiral selection rule as in the unstrained TMD region, demonstrating that the chiral selection rule of SHG is insensitive to local strain. Our findings will increase the applicability of TMD heterobilayers in nonlinear optoelectronics and valleytronics.
