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Optical Injection Phase-Locked Loop Application in Continuous-variable Quantum Key Distributions

Khaksar, Zeinab Sadat | 2023

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 57045 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Bahrampour, Alireza
  7. Abstract:
  8. The primary objective of this thesis is to provide solutions addressing some security loopholes in continuous variables quantum key distribution protocols. The coherent detection method is utilized in this particular quantum key distribution scheme, which is a phase-sensitive detection. To measure in the quantum noise limit in the detection part, we need a local optical oscillator, which must possess a high intensity and a consistent phase correlation with the quantum signal. Therefore, reconstructing the emitter’s reference phase in the receiver’s detection system is considered as one of the most critical challenges in these protocols. In order to attain this goal, in the early versions of these protocols, the quantum and phase reference signals were produced from the same laser and sent by the emitter. Nevertheless, the high intensity of the classical reference signal not only introduces structural complexities to these protocols but also poses a significant risk to their security. By reporting several attacks on these protocols due to in-line high-intensity local oscillators, some researchers suggested locally estimating the phase reference of the carrier signal at the receiver using phase estimation algorithms and without sending the high classical intensity signal. Despite removing the problems caused by sending the carrier signal, this method introduced additional computational complexity and noise into the system. In this thesis, firstly, we made an attempt to minimize the changes in the laser parameters due to temperature changes as the emitter source of information by conducting an analytical investigation into the temperature distribution and control in semiconductor lasers. Specifically, we explore the efficacy of the Peltier cooler, to reduce the imposed noise on the system. In the second step, we proposed the optical injection phase-locked loop method to reconstruct the reference signal in the detection system. At this stage, we showed that this method has a significant role in reducing noise and increasing the quantum key distribution range. In the third phase, a QKD protocol was suggested to transmit quantum and classical signals concurrently. The proposed methodology incorporates the utilization of the reference signal alongside carrier reconstruction to transmit the classical binary phase-shift keying modulated information
  9. Keywords:
  10. Cooler Thermoelectrics ; Wavelets ; Gaussian Modulated Coherent State-Continuous Variable Quantum Key Distribution (GMSC-CV-QKD) ; Distributed Bragg Reflector (DBR)Laser ; Optical Phase-Locked Loop (OPLL) ; Optical Injection-Phase Locked Loop (OIPLL) ; Binary Phase Shift Keying (BPSK) ; Simultaneous Quantum and Classical Communication (SQCC)Protocol

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