Overcoming Excitation Loss in Quantum Systems
The benefit of applying quantum mechanical principles to carrying out information processing tasks has become widely acknowledged. Yet, in practice, the inevitable coupling between quantum systems and the environment can cause quantum information to decohere and tasks to fail. In this thesis, we theoretically investigate schemes that protect quantum states from the excitation loss error process. Concerning long distance quantum communication for which channel attenuation is a key bottleneck, we study the approach of quantum repeater (QR) and systematically compare QR protocols to identify suitable architectures for different experimental scenarios. Concerning the protection against excitation loss using the large Hilbert space of a bosonic mode, we study a number of bosonic codes, their recovery operations and performances. We also demonstrate the critical role that phase degree of freedom can play in efficient code constructs. We hope the results developed here can lead to more robust quantum communication and error-corrected quantum computation.