Details
Originalsprache  Englisch 

Qualifikation  Doctor rerum naturalium 
Gradverleihende Hochschule  
Betreut von 

Datum der Verleihung des Grades  22 Sept. 2022 
Erscheinungsort  Hannover 
Publikationsstatus  Veröffentlicht  2023 
Abstract
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Hannover, 2023. 181 S.
Publikation: Qualifikations/Studienabschlussarbeit › Dissertation
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TY  BOOK
T1  Development of semiconductor light sources for photonicenabled quantum communication
AU  Yang, Jingzhong
N1  Doctoral thesis
PY  2023
Y1  2023
N2  Quantum information technologies have attracted tremendous attentions and development efforts by worldwide research organizations and governments in the past decades. It comprises the generation, manipulation, and transfer of quantum bits `qubits' based on the laws of quantum mechanics, enabling the applications of quantum metrology, quantum computation, quantum communication, etc. As one of the frontier quantum technologies, quantum communication features unconditionally secure data transfer between parties over long distance in theory, which can be accomplished through quantum state of light photons, due to their weak interaction with the environment and their remaining coherence over long distance. Meanwhile, quantum repeaters, similar as amplifier in classical communication are believed to be indispensable components to address the photon absorption and decoherence in noisy quantum channels, which scales exponentially with the distance. Quantum repeaters generally consist of three basic elements, namely entanglement swapping, entanglement purification, and quantum memories. In spite of significant breakthroughs achieved with a variety of optical protocols theoretically and experimentally, lack of nearperfect deterministic light sources with fast repetition rates, high degree of single photon purity, indistinguishability, and entanglement still impedes the practical applications. Semiconductor quantum dots are one of the leading system that have exhibited their potential for ondemand generation of highquality single and entangled photon pairs for above applications. In this work, epitaxially grown IIIV semiconductor quantum dots are investigated for driving their application in future quantum networks. First, an individual quantum dot emitting two pairs of entangled photons under pulsed twophoton resonant excitation has been utilized for realization of entanglement swapping, with the swapped photon pairs yielding a fidelity of 0.81 ± 0.04 to the Bell state Ψ+. To explore the practical limits of future quantum networks featuring multiple semiconductor based sources, we scrutinize the consequences of device fabrication, dynamic tuning techniques, time evolution of entanglement, and statistical effects on two separated quantum dot devices adapted in an entanglement swapping scheme. A numerical model based on the observed experimental data is proposed, serving not only as a benchmark for scalability of quantum dot devices, but also laying a roadmap for optimization of solidstate quantum emitters in quantum networks. For realworld quantum applications envisioned with quantum dots, the brightness of the quantum light sources is one of the key enabling factors, which is determined by the source excitation and extraction efficiency, as well as system detection system efficiency. Usually, the primary issue restricting the extraction of photons from IIIV semiconductor quantum dots is the highrefractive index material of the host matrix which causes at the semiconductorvacuum interface. To improve the photon extraction efficiency, a simple and efficient structure based on the principle of optical antennas is developed, resulting in an observed extraction of 17% of single photons in the telecom Oband, and a broadband enhancement of up to 180 times compared to the asgrown sample. A further limiting factor in the source efficiency is caused by the presence of charges in the solidstate environment. Charge fluctuation occur that quench radiative emission processes in resonant excitation schemes and induce fluorescence intermittence (blinking) that deteriorates the quantum yield. The photoneutralization of GaAs/AlGaAs quantum dots excited by twophoton resonant pumping is investigated. Applying weak gate laser light to the quantum dot allows for controlling the charges capture processes. By adjusting the gate laser power and wavelength, an increase in excitation efficiency of 30% is observed compared to the twophoton resonant excitation without optical gating. The transition rates between the neutral and charged ground state are investigated by means of auto/cross correlation measurements. Furthermore, by studying a series of surfacepassivated samples with different dottosurface distance as close to 20 nm, ODT was found to be an effective compound to neutralize the surface states, leading to reduced formation of nonradiative transition channels. It is anticipated that such a passivation method paves the way of nearfield coupling related nanophotonic devices, or elimination of surface states for wellpreserved emission properties towards the development of uncapped structure, fundamentally getting rid of total internal reflection to the maximum extent.
AB  Quantum information technologies have attracted tremendous attentions and development efforts by worldwide research organizations and governments in the past decades. It comprises the generation, manipulation, and transfer of quantum bits `qubits' based on the laws of quantum mechanics, enabling the applications of quantum metrology, quantum computation, quantum communication, etc. As one of the frontier quantum technologies, quantum communication features unconditionally secure data transfer between parties over long distance in theory, which can be accomplished through quantum state of light photons, due to their weak interaction with the environment and their remaining coherence over long distance. Meanwhile, quantum repeaters, similar as amplifier in classical communication are believed to be indispensable components to address the photon absorption and decoherence in noisy quantum channels, which scales exponentially with the distance. Quantum repeaters generally consist of three basic elements, namely entanglement swapping, entanglement purification, and quantum memories. In spite of significant breakthroughs achieved with a variety of optical protocols theoretically and experimentally, lack of nearperfect deterministic light sources with fast repetition rates, high degree of single photon purity, indistinguishability, and entanglement still impedes the practical applications. Semiconductor quantum dots are one of the leading system that have exhibited their potential for ondemand generation of highquality single and entangled photon pairs for above applications. In this work, epitaxially grown IIIV semiconductor quantum dots are investigated for driving their application in future quantum networks. First, an individual quantum dot emitting two pairs of entangled photons under pulsed twophoton resonant excitation has been utilized for realization of entanglement swapping, with the swapped photon pairs yielding a fidelity of 0.81 ± 0.04 to the Bell state Ψ+. To explore the practical limits of future quantum networks featuring multiple semiconductor based sources, we scrutinize the consequences of device fabrication, dynamic tuning techniques, time evolution of entanglement, and statistical effects on two separated quantum dot devices adapted in an entanglement swapping scheme. A numerical model based on the observed experimental data is proposed, serving not only as a benchmark for scalability of quantum dot devices, but also laying a roadmap for optimization of solidstate quantum emitters in quantum networks. For realworld quantum applications envisioned with quantum dots, the brightness of the quantum light sources is one of the key enabling factors, which is determined by the source excitation and extraction efficiency, as well as system detection system efficiency. Usually, the primary issue restricting the extraction of photons from IIIV semiconductor quantum dots is the highrefractive index material of the host matrix which causes at the semiconductorvacuum interface. To improve the photon extraction efficiency, a simple and efficient structure based on the principle of optical antennas is developed, resulting in an observed extraction of 17% of single photons in the telecom Oband, and a broadband enhancement of up to 180 times compared to the asgrown sample. A further limiting factor in the source efficiency is caused by the presence of charges in the solidstate environment. Charge fluctuation occur that quench radiative emission processes in resonant excitation schemes and induce fluorescence intermittence (blinking) that deteriorates the quantum yield. The photoneutralization of GaAs/AlGaAs quantum dots excited by twophoton resonant pumping is investigated. Applying weak gate laser light to the quantum dot allows for controlling the charges capture processes. By adjusting the gate laser power and wavelength, an increase in excitation efficiency of 30% is observed compared to the twophoton resonant excitation without optical gating. The transition rates between the neutral and charged ground state are investigated by means of auto/cross correlation measurements. Furthermore, by studying a series of surfacepassivated samples with different dottosurface distance as close to 20 nm, ODT was found to be an effective compound to neutralize the surface states, leading to reduced formation of nonradiative transition channels. It is anticipated that such a passivation method paves the way of nearfield coupling related nanophotonic devices, or elimination of surface states for wellpreserved emission properties towards the development of uncapped structure, fundamentally getting rid of total internal reflection to the maximum extent.
U2  10.15488/13225
DO  10.15488/13225
M3  Doctoral thesis
CY  Hannover
ER 