Resonance fluorescence of novel quantum emitters

Abstract

Quantum dots (QD) emitting near the telecommunication O-band and excitons believed to be localized on defects in WSe2 monolayers are investigated using optical spectroscopy and resonance fluorescence (RF). The development of light sources emitting around 1300 nm is motivated primarily by the possibility of their use in information communication applications. The results presented in this thesis pave the way towards coherently generated indistinguishable single photons and entangled photon pairs at telecom wavelengths. WSe2 monolayers are highly stable and are characterized by a higher extraction efficiency of photons compared to photon sources embedded in bulk materials. The experiments on confined excitons described here set the stage for the characterization of the effect of valley pseudospin on localized exciton emission properties. A perturbative Coulomb blockade model is applied to telecom wavelength QDs to extract confinement and interaction energies, demonstrating that carriers are in the strong confinement regime. To examine the effect of strong confinement on carrier properties, photoluminescence (PL) spectroscopy of single QDs in the pres- ence of external electric and magnetic fields is performed, and the permanent dipole moment, polarizability, diamagnetic coefficient, and g-factor of excitons localized within them are measured. Temporal measurements on neutral and charged exci- tons are performed, and a bi-exponential decay is observed in the former case, which necessitates a spin-flip interaction with the Fermi sea. RF of telecom wavelength QDs is demonstrated, and numerical simulations are used to characterize the effect of spectral fluctuations resultant from charge noise on RF linewidth. Performing high-resolution spectroscopy, the Mollow triplet is observed and dephasing in the system is shown to be negligible. Second-order correlation function measurements of emission from a localized ex- citon in a WSe2 monolayer cooled to 4 K under non-resonant and resonant excitation demonstrate its single photon nature. High-resolution PL excitation spectroscopy is used to identify a weakly-fluorescent exciton state blue-shifted from the ground- state exciton. Resonance excitation of the blue-shifted exciton is shown to produce single photons of high purity from the lowest energy exciton state.