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Explicit Abelian Lifts and Quantum LDPC Codes

Talkat ITCS 2022 · 2022-01-31..02-03· [quantum-computing]
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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.

AI-written summary · about

  1. 0:00Intro
  2. 0:44OUTLINE
  3. 1:25Expansion
  4. 4:14Symmetry
  5. 6:412 REASONS WHY
  6. 10:10Known Techniques
  7. 12:43(H) lift of a graph
  8. 13:51Example (revisited)
  9. 14:45Properties of lifting
  10. 16:25Quick history of lifting
  11. 18:10Can we lift more?
  12. 19:10Main Result (Simplified)
  13. 22:11Application - LDPC Codes
  14. 24:27Trace Power method
  15. 27:13Longer hikes are harder!
  16. 28:29Counting via DFS
  17. 30:47Summary
  18. 31:51Open Problems
  19. 33:36Thank you!
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