Engineering the optical quality of quantum emitters in WSe₂

Abstract

Monolayer WSe₂ is an exciting novel two-dimensional platform hosting localised single photon emitters. These single photons are of particular interest as they are the building blocks for many quantum technologies including quantum communication and quantum computing. This thesis focusses on the optical properties of these emitters, and how we can improve them through device engineering and alternative excitation regimes. In this thesis, I demonstrate devices with optimised design to produce stable emitters leading to reduced spectral wander. I realise this by encapsulating the monolayer in hBN, or by suspending the monolayer. This supports the theory that most spectral wander in these emitters arises from local charge traps in the substrate that contribute to charge noise. I further optimise the fabrication steps to build complex heterostructures allowing for application of electric fields and for a Coulomb blockade effect where we were able to deterministically tunnel a desired charge into the emitter. Further, I present the results of photoluminescence excitation measurements. Using this, I identify a quasi-resonant excitation regime giving rise to clean and stable single photon emission. In addition to this, these resonances provide an insight into the relationship between the emitters and the unbound excitons in the monolayer. Finally, a requirement for a coherent spin-photon interface in this system is to optically access a local spin ground state. I present our effort towards demonstrating a coherent spin-photon interface through resonance fluorescence. I elaborate on the challenges of this approach and discuss future work necessary to develop a spin-photon interface in this material examined.