에너지 장벽을 활용한 전자 파동 묶음의 조작 및 특성화 = Characterization and manipulation of single-electron wave packet by using energy barrier

다국어 초록 (Multilingual Abstract)

The controlled generation and manipulation of single electrons in mesoscopic systems are fundamental techniques for realizing advanced quantum-optical experiments. A dynamic quantum dot formed in a GaAs/AlGaAs two-dimensional electron gas (2DEG) can be an excellent source for generating hot single electrons on demand, as it isolates the electrons from the Fermi sea, making it an ideal platform for precise single-electron control.

In this study, the wave packets of the emitted electrons were tuned and examined through electrostatic control using various surface gates in both the time and energy domains. In particular, side gates placed along the transport channel were employed to modify the edge confinement potential, thereby suppressing longitudinal optical phonon scattering and enhancing the integrity of the wave packet. Furthermore, a quantum point contact served as an energy filter to selectively transmit or reflect electrons according to their kinetic energy, enabling controlled manipulation of the spectral width of the wave packet.

To obtain a full characterization of the emitted wave packet, a continuous-variable electron tomography technique was implemented, reconstructing the Wigner distribution in the time-energy phase space from a series of time- and energy-resolved measurements. The reconstructed Wigner distribution revealed that the filtering process effectively removed the low-energy components of the wave packet without significant temporal distortion.

Overall, this work establishes a practical scheme for the controlled generation, manipulation, and tomographic characterization of single-electron wave packets in GaAs/AlGaAs 2DEG devices, providing a robust experimental basis for future electron-based quantum-optical experiments in solid-state systems.

목차 (Table of Contents)

• Chapter 1. Introduction 1
• Chapter 2. Theoretical Background 4
• 2.1. A 2DEG System based on a GaAs/AlGaAs Heterostructure 4
• 2.2. Representative Quantum Devices in a 2DEG System 10
• 2.2.1. Quantum Point Contact 10
• 2.2.2. Quantum Dot 14
• 2.2.3. Single-Electron Pump 19
• 2.2.4. Quantum Hall Device 23
• 2.3. Functional Roles of Surface Gates 27
• 2.3.1. QPC Gate as an Energy Filter 27
• 2.3.2. Side Gate with DC bias 30
• 2.3.3. Detector Gate 32
• 2.4. Electron Tomography 35
• Chapter 3. Fabrication and Experimental Setup 39
• 3.1. Device Fabrication 39
• 3.1.1. Mesa Formation 39
• 3.1.2. Ohmic Contact 42
• 3.1.3. Nano-Scale Gate Patterning 45
• 3.1.4. Large-Area Pad Patterning 47
• 3.2. Dilution Refrigerator 50
• 3.3. Bias Cooling 52
• 3.4. Measurement Configuration 55
• Chapter 4. Wave Packet Manipulation and Characterization 58
• 4.1. Device Operation 58
• 4.1.1. Side Gate with DC bias 63
• 4.1.2. QPC Gate as an Energy Filter 66
• 4.2. Experimental Electron Tomography 70
• Chapter 5. Conclusion 81
• Appendix. Notes on the Wigner Distribution Derivation 83
• References 92
• Abstract in Korean 102