June2026 updates to 01_QEC_Intro

[justinlietz]

Summary

Updates QEC101 Lesson 01 and its solution notebook for correctness and clarity.

Key changes:

• Corrects threshold-theory wording so classical and quantum EC both acknowledge threshold behavior.
• Clarifies repetition-code correction as majority vote before introducing syndrome/decoder terminology.
• Defines syndrome in the Hamming-code section as parity-check disagreements.
• Fixes Hamming-code parity example and expected syndrome output.
• Clarifies QEC digitization: coherent and incoherent errors can be represented with error operators, and syndrome measurement reduces correction to discrete Pauli error classes.
• Tightens stabilizer wording around +1/-1 eigenvalues and syndrome extraction.
• Fixes the final quantum repetition-code logical error rate calculation.