This is a simplified, lossless Mach–Zehnder interferometer with balanced beam splitters. With coherent paths and the recombiner in place, the model uses P(A) = cos²(φ/2) and P(B) = sin²(φ/2). The phase control includes fixed optical phase offsets.
The glowing paths illustrate probability amplitudes, not two half-photons or measured trajectories. Each emitted photon produces exactly one output detection. The path-record control represents an ideal non-absorbing path measurement: it removes interference without removing photons. Ordinary photon counters often absorb the light.
Random samples fluctuate. Mission scores depend on the configured probabilities and apparatus, rather than lucky counts. Turning off the path recorder affects future photons; it does not erase past measurements.
Explore the foundations: Feynman’s Quantum Behavior · IBM Quantum: Single systems.