Resonant Excitation Spectroscopy and Photon Statistics of Self-assembled Semiconductor Quantum Dots

Abstract

Light-matter interactions in semiconductor nanostructures have attracted significant research interest because of both fundamental physics questions and practical concerns. Epitaxially grown quantum dots (QDs), with their narrow emission linewidths and atom-like density of states in a solid state system, are archetypical elements of study and are potentially useful for many applications, such as on-demand single photon emitters [1,2], efficient entangled photon-pair sources [3,4], and cavity quantum electrodynamics (QED) research [5–11]. Most experiments employ resonant or near-resonant excitation to directly interact with the bound states, which enables high excitation efficiency, precise control of quantum states, and minimal disturbance of the local environment. However, the inevitable doping of the material in growth introduces an intrinsic free charge carrier reservoir that enables charge fluctuations of the QD and defects in its surrounding local environment. The direct consequences are fluorescent intermittency (or blinking) in a QD’s emission, and spectral diffusion of the QD’s energy level. Both effects pose challenges for using these photons as flying qubits to realize a quantum network or linear optical quantum computing. Blinking compromises the properties of these QDs useful for generating on-demand single photons. Characterizing these charge dynamics and understanding the underlying physics is critical for hunting potential methods to suppress them. In this dissertation, by examining the excitation spectra of the QD and the photon statistics of its emission, we are able to determine the possible trap locations and the time scale of these charge dynamics. In fact, the temporal correlation measurement captures both the non-classical nature of these quantum emitters and the charge dynamics of both the QD and nearby defects. This information helps identify the nature of these charge traps, and provides the clues for suppressing these electric fluctuations; for example, by modifying the sample growth parameters or fabricating additional nano-structures on the sample to deplete the free charge carriers. One solution to these problems is to use a better sample with less intrinsic doping. It has been demonstrated that the photons emitted from the same QD in rapid succession can have very high indistinguishability when the QD is in an optical cavity [12,13] or is excited resonantly [14]. However, photons spaced widely in time and those from separate QDs do not show the same degree of indistinguishability [15–17] due to the inhomogeneous distribution of photon energies emitted by one QD state at different times. Considering that the state-of-art growth technique cannot achieve zero-doping growth, nor