t b a b a

which means that the stabilizer M commutes with one of the two errors E T F1, E T F2 and
anti-commutes with the other. So error E T F1 is distinguishable from error E T F2. Therefore,
if we know the exact prior errors E, we can identify and correct any E T Fi errors with the
weight of Fi equal or less than eu.
For example, consider a 5-qubit quantum error-correcting code Q with n = 5 and k = 1.
The logical codewords for Q are:
| 0L〉 = 1
4 [| 00000〉+ | 10010〉+ | 01001〉+ | 10100〉+ | 01010〉− | 11011〉− | 00110〉− | 11000〉
− | 11101〉− | 00011〉− | 11110〉− | 01111〉− | 10001〉− | 01100〉− | 10111〉− | 00101〉]
| 1L〉 = 1
4 [| 11111〉+ | 01101〉+ | 10110〉+ | 01011〉+ | 10101〉− | 00100〉− | 11001〉− | 00111〉
− | 00010〉− | 11100〉− | 00001〉− | 10000〉− | 01110〉− | 10011〉− | 01000〉− | 11010〉]
The stabilizer S of this code is described by a group of 4 generators:
M1 = σx ⊗ σz ⊗ σz ⊗ σx ⊗ σI, M2 = σI ⊗ σx ⊗ σz ⊗ σz ⊗ σx,
M3 = σx ⊗ σI ⊗ σx ⊗ σz ⊗ σz, M4 = σz ⊗ σx ⊗ σI ⊗ σx ⊗ σz.
It is easy to see that two codewords are eigenvectors of the stabilizers with an eigenvalue of
(+1):
Mj | 0L〉 = (+1) | 0L〉 and Mj | 1L〉 = (+1) | 1L〉, 1 ≤ j ≤ 4.
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