Interferometer Loss Ceiling Boundary Scan - Quantum Mechanics IV: Photons, Interferometers, and Optical Qubits Step by Step

An interferometer loss ceiling scan checks whether the number of lost photons stays within a maximum allowance, so blocking too many photons fails the gate. The three rows give lost counts 0, 4, and 6 against ceiling 4, yielding margins 4, 0, and -2 (pass, pass, fail) exactly for the stated toy photon budget; real interferometers have loss calibration, detector efficiency, alignment, dark counts, and finite-shot uncertainty.

Blocked-arm loss is counted against a ceiling. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

Path loss is compared with a ceiling

The unblocked row has no lost photons.

m=N_{\max\ \text{lost}}-N_{\text{lost}}

Blocked-arm rows bracket the loss ceiling

Blocking half of eight photons is the boundary. Blocking half of twelve exceeds it.

\begin{array}{c|c|c|c}N_{\text{in}}&N_{\text{lost}}&m&\text{gate}\\8&0&4&\text{pass}\\8&4&0&\text{pass}\\12&6&-2&\text{fail}\\\end{array}

The larger blocked packet exceeds the loss ceiling

The interferometer helper closes bright plus dark plus lost counts before the gate is checked.

m=-2\quad \text{fail}