Photonic and electric control of single photon emission from individual quantum dots

Abstract

Modern single photon quantum technologies require on-demand and deterministic sources. Single photon emission has been observed from various solid state systems, such as individual molecules, defects and colour centres in diamond and 2D materials, and artificial atoms - quantum dots. However, the quantum emitters suffer from the slow radiation rate and omnidirectional emission, preventing their practical applications. First, this Thesis proposes to exploit the charged excitonic states in individual colloidal quantum dots for the enhancement of radiation rate. Electron injection to a quantum dot increases the number of de-excitation pathways, hence boosting the single photon generation speed. The optical properties of charged excitons depend drastically on the number of injected electrons, which can be controlled by applying a voltage bias in an electrochemical cell, thus providing for an active and deterministic way to manipulate the single photon emission. The charge transfer allows for a deterministic manipulation of quantum dot photodynamics, with an observed 210-fold increase of the radiation rate, accompanied by a 12-fold decrease of the emission intensity, all while preserving single-photon emission characteristics. Secondly, this Thesis proposes a 3D metal-dielectric parabolic antenna with an individual quantum dot in its focal point as a source of collimated single photons which can then be easily extracted and manipulated. Compared to conventional nano-antennas, 3D parabolic antenna design does not require near-field coupling, hence it is very robust against misalignment issues, and minimally affected by absorption in the metal. The parabolic antenna provides one of the largest reported experimental directivity (D=106) and the lowest beam divergence (13.5 deg), a broadband operation over all the visible and near-IR range, together with more than 96% extraction efficiency, offering a practical advantage for quantum technological applications.