Explicit Abelian Lifts and Quantum LDPC Codes
summary
Constructs polynomial-time explicit d-regular expanders that are Z_L lifts (and more generally transitive abelian lifts) for L up to about 2^{cN}, derandomizing prior existential results and producing explicit quasi-cyclic LDPC and quantum LDPC codes with distance nearly N^{1−α} (and almost linear distance in some regimes). Analysis uses the trace power/trace-bar method plus a new combinatorial count of hikes (singleton-free nonbacktracking walks) via compressed DFS encodings, yielding near-Ramanujan eigenvalue bounds in the stated ranges.
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chapters (19)
- 0:00Intro
- 0:44OUTLINE
- 1:25Expansion
- 4:14Symmetry
- 6:412 REASONS WHY
- 10:10Known Techniques
- 12:43(H) lift of a graph
- 13:51Example (revisited)
- 14:45Properties of lifting
- 16:25Quick history of lifting
- 18:10Can we lift more?
- 19:10Main Result (Simplified)
- 22:11Application - LDPC Codes
- 24:27Trace Power method
- 27:13Longer hikes are harder!
- 28:29Counting via DFS
- 30:47Summary
- 31:51Open Problems
- 33:36Thank you!
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