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.