Spinnler, Clemens. Exploiting phonon and coulomb interactions in semiconductor quantum dots. 2023, Doctoral Thesis, University of Basel, Faculty of Science.

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Abstract
Semiconductor quantum dots have been investigated in many different aspects, from fundamental semiconductor physics to advanced quantum technologies. After many years of growth improvements, the quantum dot emits single photons of high purity and high indistinguishability. The noise in the semiconductor is reduced to a level where it starts to be negligible (compared to other measurement errors). Recently advances also have been made in controlling a single electron(hole)spin confined by the quantum dot. This makes the quantum dot a perfect candidate for any application involving single photons and also a spin, for example, boson sampling and cluster state generation, respectively.
The quantum dot can also be used to study its coupling to additional degrees of freedom, such as for example the surrounding nuclear spins or coupling to an optical cavity. In this thesis, two individual studies are presented. First, the interaction of the quantum dot with the mechanical surrounding, i.e. phonons, and second, radiative Auger processes due to Coulomb interactions.
The quantum dot naturally couples to its mechanical environment by deformationpotential coupling. The interaction is exploited by engineering the mechanical environment (density of states) by patterning a mechanical resonator (mechanical cavity). The main focus lies on reaching gigahertz mechanical frequencies, the socalled resolvedsideband regime. However, this is not trivial for two reasons. First, fabricating a mechanical resonator at such high frequencies is challenging due the small size. Second, measuring such a fast modulation of the quantum dot requires a special measurement parameter set. Nonetheless, the coupling to mechanical resonators from a few megahertz to more than a gigahertz mechanical frequency is shown. Furthermore, an indepth study of the excitonphonon interaction is presented which includes a semiclassical masterequation description of the coupled system as well as the observation of acoustic sideband emission. The current limit, for applications such as optomechanical cooling, is the coupling rate between the two systems. However, such experiments are within reach with a five to tenfold increase in the coupling rate.
The quantum dot itself presents a coupled system if charged with an additional electron (or hole). Then, in the excited state, three carriers (one hole and two electrons) are tightly confined inside the dot which are coupled to each other via Coulomb interactions. The effect of this coupling is studied which gives rise to the socalled radiative Auger process. During the decay of the trion, one of the carriers (the Auger electron) is promoted to a higher energy state inside the quantum dot (p and dshell) and the emitted photon is correspondingly redshifted. In more detail, it is found that the wavefunction of the trion is composed of admixtures of higher shells and the emitted photon projects the state of the remaining electron to the corresponding shell. Furthermore, the radiative Auger process gives rise to an optical transition which can be addressed with a laser. In a twolaser experiment (Λconfiguration), the radiative Auger transition is optically driven. This leads to a coherent superposition of the auger carrier being in two different quantum dot shells. These measurements pose a first step toward coherent control of the orbital state of the Auger carrier.
The quantum dot can also be used to study its coupling to additional degrees of freedom, such as for example the surrounding nuclear spins or coupling to an optical cavity. In this thesis, two individual studies are presented. First, the interaction of the quantum dot with the mechanical surrounding, i.e. phonons, and second, radiative Auger processes due to Coulomb interactions.
The quantum dot naturally couples to its mechanical environment by deformationpotential coupling. The interaction is exploited by engineering the mechanical environment (density of states) by patterning a mechanical resonator (mechanical cavity). The main focus lies on reaching gigahertz mechanical frequencies, the socalled resolvedsideband regime. However, this is not trivial for two reasons. First, fabricating a mechanical resonator at such high frequencies is challenging due the small size. Second, measuring such a fast modulation of the quantum dot requires a special measurement parameter set. Nonetheless, the coupling to mechanical resonators from a few megahertz to more than a gigahertz mechanical frequency is shown. Furthermore, an indepth study of the excitonphonon interaction is presented which includes a semiclassical masterequation description of the coupled system as well as the observation of acoustic sideband emission. The current limit, for applications such as optomechanical cooling, is the coupling rate between the two systems. However, such experiments are within reach with a five to tenfold increase in the coupling rate.
The quantum dot itself presents a coupled system if charged with an additional electron (or hole). Then, in the excited state, three carriers (one hole and two electrons) are tightly confined inside the dot which are coupled to each other via Coulomb interactions. The effect of this coupling is studied which gives rise to the socalled radiative Auger process. During the decay of the trion, one of the carriers (the Auger electron) is promoted to a higher energy state inside the quantum dot (p and dshell) and the emitted photon is correspondingly redshifted. In more detail, it is found that the wavefunction of the trion is composed of admixtures of higher shells and the emitted photon projects the state of the remaining electron to the corresponding shell. Furthermore, the radiative Auger process gives rise to an optical transition which can be addressed with a laser. In a twolaser experiment (Λconfiguration), the radiative Auger transition is optically driven. This leads to a coherent superposition of the auger carrier being in two different quantum dot shells. These measurements pose a first step toward coherent control of the orbital state of the Auger carrier.
Advisors:  Warburton, Richard J 

Committee Members:  Poggio, Martino and Claudon, Julien 
Faculties and Departments:  05 Faculty of Science > Departement Physik > Physik > Experimental Physics (Warburton) 05 Faculty of Science > Departement Physik > Physik > Nanotechnologie Argovia (Poggio) 
UniBasel Contributors:  Poggio, Martino 
Item Type:  Thesis 
Thesis Subtype:  Doctoral Thesis 
Thesis no:  15100 
Thesis status:  Complete 
Number of Pages:  v, 182 
Language:  English 
Identification Number: 

edoc DOI:  
Last Modified:  01 Sep 2023 04:30 
Deposited On:  31 Aug 2023 11:13 
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