Single-Photon Emission from Monolayer 2D Materials Coupled with Chiral Plasmonic Nanoparticles

The single-photon emitter carrying spin angular momentum is a key component in quantum information and quantum cryptography, promising highly secure information processing without leakage. Nonreciprocal single-photon configurations and deterministic spin-photon interfaces are possible with chiral quantum optics. Recently, quantum confinement in atomically thin transition metal dichalcogenides (TMDCs) has been investigated for single-photon emission based on naturally or artificially occurring defects. By applying mechanical strains to the TMDCs, it is feasible to precisely control the position and polarization of a single-photon emitter [1]. Strains in TMDCs have been induced using various nanostructures including dielectric pillars and nanogaps. In this work, we demonstrate a new type of single-photon emitter with chirality. Atomically thin tungsten diselenide (WSe₂) is placed on silica-encapsulated plasmonic chiral nanoparticles [2]. As a result of efficient coupling between the single-photon emitter and the chiral plasmonic nanoparticle, Purcell enhancement and increased intensity from the single-photon emitter were observed, showing circular or elliptical polarization directions. In the experiment, we observed that strain-induced single-photon emission with a chiral nanoparticle was &gt;10 times stronger than unstrained WSe₂ photoluminescence. The single-photon characteristics were clarified using the Hanbury-Brown and Twiss (HBT) measurement setup. Furthermore, due to the coupling with the metal nanoparticle, the single-photon emitter had the reduced lifetime (0.8 ns) compared to the uncoupled emitter (20 ns). By measuring the polarization of the emitter coupled with the chiral nanoparticles, a degree of circular polarization of 0.8 was obtained. Last, numerical simulation demonstrated that chiral nanoparticles can generate spin angular momentum. Therefore, our approach will be useful for demonstrating a quantum light source for next-generation photonic integrated circuits.<br/><br/>References<br/>Jae-Pil So, Kwang-Yong Jeong, Jung Min Lee, Kyoung-Ho Kim, Soon-Jae Lee, Woong Huh, Ha-Reem Kim, Jae-Hyuck Choi, Jin Myung Kim, Yoon Seok Kim, Chul-Ho Lee, SungWoo Nam, and Hong-Gyu Park, “Polarization control of deterministic single-photon emitters in monolayer WSe₂,” <i>Nano Letters</i> 21, 1546-1554 (2021).<br/>Hye-Eun Lee, Hyo-Yong Ahn, Jungho Mun , Yoon Young Lee , Minkyung Kim, Nam Heon Cho , Kiseok Chang, Wook Sung Kim, Junsuk Rho, and Ki Tae Nam, “Amino-acid- and peptide-directed synthesis of chiral plasmonic gold nanoparticles,” <i>Nature</i> <b>556</b>, 360-365 (2018)