Quantum Eraser — Which-Path Interference

Setup

Slit separation d: 4.0 Wavelength λ: 550 nm Slit width a: 1.0 Screen distance L: 3.0

Which-Path Marker

Path distinguishability D: 0.00

Eraser

Observables

Visibility V—

Distinguishability D—

V²+D²—

Fringe spacing—

Pattern—

Duality relation: V² + D² ≤ 1.

With which-path info (D→1): interference fringes disappear (V→0). The eraser destroys path info, restoring fringes — even when the choice is made after detection (delayed-choice).