Resources:
https://youtu.be/8ORLN_KwAgs
https://en.wikipedia.org/wiki/Delayed-choice_quantum_eraser
Solution Part 1:
The experiment shown in the diagram is the Delayed Choice Quantum Eraser Double Slit Experiment.
This experiment breaks time itself by entangling a particle (photon) through a crystal after a double slit. The entangled particle on the North Path hits Detector 0 (not labeled) first, while the South Path adds post-processing. Because of the bizzare nature of entanglement, the two correspond instantaneously without regard to distance, or in this experiment, time.
The first set of half-mirrors reflect half of the particles to either Detector 1 or Detector 2. These first 2 detectors on the South Path retain information about which slit the particle passed through. So the resulting pattern we see on the North Path is particle-like (two bands). But if the particle passes through the first half mirrors to the dark black full mirrors, it reflects through a scrambling filter on the way to Detector 3. At Detector 3 the which-path information is destroyed, so the North Path retroactively registers wave-like patterns.
Based on this information, we can conclude that the measurement we are seeing on the North Path corresponds to Detector 3, because the which-path information was destroyed.
Solution Part 2
If we destroy every 3rd letter in the string of letters SILNZEANGIA ESEPCZUANGIA, we get
SINZANIA SECZANIA
Solution Part 3
Sine (Sin) and Secant (Sec) are trigonometric operations. Secant is the inverse of Cosine (Cos). Substituting, we get Sin x Sec = Sin / Cos = Tangent (Tan). This leads us to the answer, Tanz[a]nia.