PhD defence by Yonghe Yu

Abstract

Quantum technology has already led to revolutionary applications in areas such as quantum communication, quantum computing, and quantum precision measurement. To enable the transmission of quantum states between quantum computers on a global scale, researchers have developed quantum networks based on quantum repeaters, which form an important branch of quantum communication.

Among the platforms for implementing the quantum information processing required in quantum repeaters, integrated photonics has attracted significant attention due to its scalability, stability, low cost, and room-temperature operation. Since the core experiment of a quantum repeater is entanglement swapping, this work presents several chip-based experiments surrounding entanglement swapping.

The first experiment demonstrates an on-chip photon buffer with 100 ps resolution, which can enhance the swapping rate in entanglement swapping under high channel loss. This device achieves the highest photon storage resolution reported to date. We also show its application as the first on-chip temporally multiplexed single-photon source. The second part demonstrates the first on-chip entanglement purification experiment. Entanglement purification maintains high-quality entanglement distribution in noisy channels and improves the fidelity of entanglement swapping. Finally, in the third experiment, I designed an on-chip circuit that realizes the first chip-to-chip entanglement swapping. The circuit integrates a high-quality on-chip entangled pair source and is expected to enable high-rate entanglement swapping.

In summary, my work demonstrates efforts to realize entanglement swapping with integrated photonics as a step toward chip-based quantum repeaters. The three experiments shown in this work correspond to the three essential components of a quantum repeater.

Supervisors

• Principal supervisor: Senior Researcher Yunhong Ding, Department of Electrical and Photonics Engineering, DTU, Denmark

•  Co-supervisor: Professor Karsten Rottwitt, Department of Electrical and Photonics Engineering, DTU, Denmark

• Co-supervisor: Professor Leif Katsuo Oxenløwe, Department of Electrical and Photonics Engineering, DTU, Denmark

Evaluation Board

• Senior Researcher Elizaveta Semenova, Department of Electrical and Photonics Engineering, DTU, Denmark

• Associate Professor Stefano Paesani, Niels Bohr Institute, Copenhagen University

• Associate Professor Ali Elshaari, KTH Royal Institute of Technology, Sweden

Master of the Ceremony

• Senior Researcher Deming Kong, Department of Electrical and Photonics Engineering, DTU, Denmark