Treat leakage as a separate lost-count budget before readout. The toy channel
starts with 80 zero shots and 20 one shots, leaks away one fifth, and leaves 64
zero plus 16 one retained shots with 20 leaked shots carried outside the
computational readout; real leakage estimates depend on calibration, drift,
state preparation, detector noise, and finite-shot uncertainty.
Leakage is an erasure budget that carries lost counts separately. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Leakage splits each state into kept and lost counts
From the channel output, zero has 80 shots and one has 20. One fifth leaks away, leaving 64 zero and 16 one shots.
Nkept=(64,16)
Lost shots leave the computational readout ledger
The lost counts are 16 from zero and 4 from one, so leaked shots total 20.