Highly Polarized Single Photons from Strain-Induced Quasi-1D Localized Excitons in WSe₂

Abstract

Single photon emission from localized excitons in two-dimensional (2D) materials has been extensively investigated because of its relevance for quantum information applications. Prerequisites are the availability of photons with high purity polarization and controllable polarization orientation that can be integrated with optical cavities. Here, deformation strain along edges of prepatterned square-shaped substrate protrusions is exploited to induce quasi-one-dimensional (1D) localized excitons in WSe 2 monolayers as an elegant way to get photons that fulfill these requirements. At zero magnetic field, the emission is linearly polarized with 95% purity because exciton states are valley hybridized with equal shares of both valleys and predominant emission from excitons with a dipole moment along the elongated direction. In a strong field, one valley is favored and the linear polarization is converted to high-purity circular polarization. This deterministic control over polarization purity and orientation is a valuable asset in the context of integrated quantum photonics.

High-Density, Localized Quantum Emitters in Strained 2D Semiconductors

“…Moreover, as these mechanical strains can strongly control band structure, it is possible to use mechanical strain to tune electronic and photonic performance. , For this reason, the identification of quantum emitters (QEs) in TMDCs has generated considerable excitement in the field of 2D nanophotonics − and quantum information science and engineering . Despite these intriguing properties, the fundamental origin of quantum emission in TMDCs is not completely clear, and thus far, it is believed that emissions are formed by excitons bound to defects, − impurities, or 3D transformations (nanostructures, nanoindents) induced by the strain gradients. − ,− In addition to this fundamental question, there is a need to create a high spatial and number density of quantum emitters in 2D semiconductors. The high number density and high brightness of individual quantum emitters are needed to create dense integration of quantum light sources with other photonic elements in scalable applications.…”

Single charge control of localized excitons in heterostructures with ferroelectric thin films and two-dimensional transition metal dichalcogenides

“…6,26,55,56 Second, strong asymmetry might induce the high energy branch with a small optical oscillator strength. 10,54 In our experiment, the strong asymmetry of the confining potential might be induced by the unevenness of the substrate or wrinkling during the transfer process…”

“…This is because the monolayer WSe 2 valley degrees of freedom and spin degrees of freedom are locked, then the eigenstates at zero magnetic field are a linear superposition of the left-hand circularly polarized excitonic state | K 〉 and the right-hand circularly polarized excitonic state | K ′〉, and they have equal weights. 54 …”

A Waveguide-Integrated Two-Dimensional Light-Emitting Diode Based on p-Type WSe2/n-Type CdS Nanoribbon Heterojunction

“…Furthermore, the valley-entangled opto-spintronic characters, inherited from inversion symmetry breaking and spin–orbit coupling, − enable an expanded degree of freedom for information processing. Most importantly, the vdW layered nature of TMDs allows lattice matching-free heterointegration with other nanomaterials to form quasi-one- and zero-dimensional (quasi-1D and 0D) quantum light sources, − thanks to their flexible 2D lattice framework. To date, TMD-lased light-emitting devices (LEDs) have been extensively researched, with device architectures covering the Schottky junction, , homo/heterogeneous p–n diodes, − and tunnel junctions. − Further low-loss optical interfacing of 2D LEDs with silicon (Si)-based waveguides/nanoresonators enables additional functionality for photonic signal routing and confinement, , as essentially required in PIC systems.…”