Scene
Apparatus
path A (phase-shifted)
path B
which-path marker
Controls
Classical ball
Single photon
Phase shift, φ
0.00 π
Which-path detector
marks the path via entanglement — not a "bump"
Send one photon
Run 200, fast
Reset counts
Show the math
reveal amplitude expressions
P(D0) = cos²(φ/2) P(D1) = sin²(φ/2) V = (Pmax − Pmin) / (Pmax + Pmin) which-path on → V → 0
Detector statistics
0
D0 counts
0
D1 counts
—
fringe visibility
Fringe curve — P(D0) vs φ