Quantum Institute: Visitor Schedule

The Quantum Lunch is regularly held on Thursdays in the Theoretical Division Conference Room, TA-3, Building 123, Room 121.
For more information, contact Diego Dalvit.

October 16, 2006
10:30 AM, Monday

David Poulin,
CalTech

Iterative Decoding of Quantum Error Correcting Codes

Abstract

The optimal decoding of an error correction code is an NP-complete problem, and easy instances of this problem typically result in poor codes. Iterative decoding is a technique used to achieve sub-optimal but yet "good enough" decoding, and is at the heart of most modern (nearly capacity-achieving) coding techniques. In this talk I will present some recent developments of iterative decoding of quantum error correction codes. Ollivier and Tillich first used this technique for the decoding of quantum LDPC codes. Using the language of operator quantum error correction, I will discuss the underlying principle call the "conditional renormalization" of a quantum channel. I will illustrate its use with sever examples: concatenated quantum block codes, quantum convolutional codes, and quantum turbo codes. The results obtained from concatenation show a significant improvement over the blockwise decoding technique typically used in this context, and also indicate that the 5-qubit code's threshold is the hashing bound. Results obtained from quantum turbo codes show a behavior quite similar to their classical cousins.