Bounded Retry Loop | Turn lessons into working experiments

Starter code

module bounded_retry;
@seed(7);

fn main() {
  let q: QReg<1> = qreg[1];

  until (flag == 1) max 6 {
    H(q[0]);
    let flag: Bit = measure(q[0]);
    reset q[0];
  }

  assert probability(|0>) > 0.99;
  return flag;
}

Expected output

The seed makes the retry sequence reproducible

Output lists each until iteration

The loop stops when flag becomes 1 or the max bound is reached

reset returns the qubit to |0> after each attempt

Debugging checklist

Run the lab and find the Until iteration lines in Output

Open Trace and locate the until check for flag

Change max 6 to max 1 and compare the result

Replace H with X and confirm the loop succeeds immediately

Explain why max is required for safe repeat-until-success code

Extension challenge

Add a second measured Bit and use match after the until block to choose a correction branch.