Date&Time : 

2020 / 12 / 11 (Fri) 14:20 ~ 16:20

Location : 

Delta Building R216

Speaker : 

賴青沂 教授 (交通大學電信工程研究所)

Topic : 

Exploiting Degeneracy in Belief Propagation Decoding of Quantum Codes

Abstract : 

Quantum information needs to be protected by quantum error-correcting codes due to imperfect quantum devices and operations. One would like to have an efficient and high-performance decoding procedure for quantum codes. A potential candidate is Pearl's belief propagation (BP), but its performance suffers from the many short cycles inherent in quantum codes. Many attempts to improve BP decoding of quantum codes have been made in the literature; however, there is a general impression that BP cannot work for topological codes, such as the surface and toric codes. In this paper, we propose a decoding algorithm (called MBP) for quantum codes based on BP but with a memory effect without any additional overhead. MBP exploits the degeneracy of quantum codes so that it has a better chance to find the most probable error or its degenerate errors. Moreover, the memory effect helps BP converge. MBP significantly improves the decoding performance of usual BP for various quantum codes, especially highly-degenerate codes (that is, codes with many low-weight stabilizers). For the surface or toric codes, our MBP decoder achieves a threshold of ~16% or ~17.5%, respectively, over the depolarizing channel.

Bio :

Ching-Yi Lai was born in Taipei, Taiwan. He received his MS in 2006 and BS in 2004 in electrical engineering from National Tsing Hua University, Hsinchu, Taiwan. He received his Ph.D. in 2013 in electrical engineering from the University of Southern California, Los Angeles, California. Currently, he is an Assistant Professor at the Institute of Communications Engineering, National Chiao Tung University, Hsinchu, Taiwan. Previously he was a postdoctoral research associate at the Centre for Quantum Software and Information, the University of Technology Sydney from December 2013 to July 2015. Then he was a postdoctoral scholar at the Institute of Information Science, Academia Sinica, Taiwan from September 2015 to July 2018. Prof. Lai received the MOST Young Scholar Fellowship (哥倫布計畫) in 2018 from the Ministry of Science and Technology, Taiwan. His research interests include coding theory, information theory, fault-tolerant quantum computation, quantum algorithm, and quantum cryptography.