Observable Scrambling Suppression at Finite Dilaton Cutoff: Quantitative Prediction and Experimental Comparison

The Maldacena–Shenker–Stanford (MSS) bound constrains the quantum Lyapunov exponent to λ ≤ 2πT/ħ, saturated by black holes and the SYK model. However, observers at finite boundary cutoff in Jackiw–Teitelboim (JT) gravity do not access the full bulk chaos. We derive a cutoff-dependent scrambling parameter κ(η) = κbulk · η, where η = Φ(ε)/Φmaxis the observer’s position on the dilaton profile. This function is monotonic and linear in the leading JT approximation, producing κ → 1 at the dilaton core and κ → 0 at the asymptotic boundary. For a finite rendering horizon at ηobs ≈ 0.5, the framework predicts κobserved ≈ 0.50. Recent solid-state NMR experiments by Li et al. [PRL 136, 060403 (2026)] extract κ = 0.45 ± 0.02 from adamantane spin dynamics, within 10% of the predicted value. The suppression factor arises mechanically from the dilaton profile ratio, requiring no ad hoc parameters. We propose experimental protocols to test the full κ(η) curve across coupling regimes.