25-Qubit Repetition Syndrome | Turn lessons into working experiments

Starter code

module qec_repetition_25;
@target("browser-stabilizer");

fn main() {
  let q: QReg<25> = qreg[25];

  X(q[6]);

  let s5: Bit = syndrome Z(q[5]) Z(q[6]);
  let s6: Bit = syndrome Z(q[6]) Z(q[7]);
  let middleError: Bit = s5 and s6;

  if (middleError == 1) {
    X(q[6]);
  }

  assert probability(|0000000000000000000000000>) > 0.99;
  return (s5, s6, middleError);
}

Expected output

Output reports the stabilizer tableau engine

The two neighboring parity checks around q[6] return syndrome bit 1

middleError becomes 1 and applies the correction

The final probability assertion passes without allocating a 2^25 state vector

Debugging checklist

Run the starter code and find the syndrome lines for s5 and s6

Confirm middleError is computed from the two neighboring syndrome bits

Move the injected X error to q[7] and update the checked pair

Open the timeline and find the syndrome phase entries

Explain why a repetition code detects bit-flip errors with adjacent Z parity checks

Extension challenge

Expand the starter to all 12 adjacent parity checks and use marker qubits q[13]..q[24] to visualize the syndrome pattern.