Quantum Dot Single-Photon Emission from Near-Field Light Excitation

Abstract

Quantum emitter single-photon emission and detection finds application in many areas including but not limited to quantum information, single-molecule spectroscopy, and quantum cryptography. Examples of single-photon sources are quantum dots (QDs), quantum wells, and single ions. By exciting a Si QD, inserted within different embedding media, with near-field light from a plasmonic near-field transducer (NFT), the single-photon emission is studied via the second-order autocorrelation function (g (2)(τ )) which is used to determine whether or not the light emitted is antibunched. One such embedding medium the QD is placed within is a near-zero index (NZI) layer which showed an enhancement of the electric field (E-field) and hence an increased rate of oscillation of the g (2)(τ ) curve. This NZI environment therefore produced more efficient single-photon emission compared to its air and Ge counterparts. A range of QD dipole moment values were tested where it was noted that an increase in the dipole moment corresponded to an increase in the g (2)(τ ) oscillation rate. The directional alignment of the dipole moment was also varied, however this did not have a significant effect on the g (2)(τ ) oscillation rate. Optically magnetic multilayer metamaterial structures were investigated by calculating the effective permeability (μeff) from refractive index calculations. First, a numerical Kramers-Kronig approximation (calculated using Simpson’s numerical integration MAT- LAB code) was utilized to identify the correct complex branch of the real part of the refractive index from its analytical imaginary part (calculated using reflection and trans- mission coefficients obtained from transfer matrix analytical calculations), thus enabling the real part to then be analytically calculated. Increasing the thicknesses of the Ge layers in a Ge-Ag(30 nm)-Ge multilayer metamaterial and calculating the associated μeff parameters, it could be seen that the largest magnetic resonance peaks associated with increasing thickness became less broadband in nature along with appearing at lower wave- lengths. In a simulation, a Si QD was then embedded in a Ge(30 nm)-Ag(30 nm)-Ge(30 nm) structure and excited via near-field light. This environment allowed for single-photon emission but no significant effect on the rate of single-photon emission, compared to the previously studied single-layer embedding structures, was present, and the autocorrela- tion curve did not regularly dip below 0.5 and therefore single-photon emission was not efficient in this particular case. The motivation for the research undertaken in this thesis can be attributed to many factors, including but not limited to the fact that single-photon emission plays a crucial role in a variety of research fields such as quantum information. Simple QDs are a good starting point for investigating single-photon emission as they can be constructed to consist of only a ground state and an excited state. More complicated future research possibilities might then involve, for example, investigating entanglement between two or more QDs. Another motivation for this research is the ability to alter the single-photon emission properties by adjusting the environment the QD is located in. Furthermore, the envi- ronment does not necessarily need to be complicated in order to alter the single-photon emission properties, it can consist of simple components such as stacks of planar layers of material such as the multilayer metamaterial structures investigated in this thesis.