This is the same GG02 CV-QKD model as the 3D flythrough, redrawn as two native 2D diagrams instead of a rendered fiber. The top panel is a single shared quadrature plane (X horizontal, P vertical): Alice's Gaussian-modulated points cluster tightly near the origin while Bob's received points, sampled live from the exact same channel equations, spread out to a wider dashed 1σ circle of radius √(bobVar). The bottom panel is a heat map of the secret key rate K computed independently at every (fiber length, excess noise) grid cell for the current VA and Eve setting — not read off the live pulses at all, but recomputed fresh from the formulas below on a 90×46 grid.
Fiber loss: T = 10^(-αL/10), α = 0.2 dB/km
Bob's outcome: X_B = √T·X_A + noise, Var(noise) = 1 + Tξ
Mutual info: I(A:B) = ½·log2( (T·V_A + 1 + Tξ) / (1 + Tξ) )
Eve's bound: χ_BE = ½·log2( ((1−T)V_A + 1 + Tξ) / (1 + Tξ) )
Secret key rate: K = max(0, I(A:B) − χ_BE) bit/pulse
Working the algebra on the grid reveals something the pulse animation alone doesn't show directly: because both I(A:B) and χBE share the identical (1+Tξ) denominator, the sign of K depends only on whether T·VA exceeds (1−T)·VA — which happens exactly when T > 0.5, i.e. loss past 3 dB, completely independent of the excess noise ξ or the modulation variance VA. The dashed vertical line on the heat map marks that fixed 3 dB / T=0.5 boundary; the bright marker shows your current (L, ξ) operating point, and everything left of the line stays secure no matter how the noise slider moves.
- VA slider — how strongly Alice modulates each pulse; widens both constellations and the heat map's color scale.
- Fiber length — sets T through the telecom attenuation law; moves the marker left/right on the heat map.
- Excess noise ξ — moves the marker up/down; changes K's magnitude but never which side of the 3 dB line it's on.
- Eve toggle — adds a fixed extra excess noise to the live channel and reddens Bob's constellation, but the security boundary itself does not move.