Watching the Horizon Break Entanglement: Measurement-Induced Collapse on a 156-Qubit Quantum Processor

We investigate measurement-induced effects on trans-horizon correlations in dynamic quantum circuits executed on IBM's 156-qubit superconducting processor (ibmfez, Heron r2 architecture). We engineer a 40-qubit spin chain with a spatially-varying XX + YY coupling profile that creates an analog horizon at position xh = 20, where coupling strength reaches a minimum. We define a correlation contrast metric C = ⟨σxiσxj⟩horizon − ⟨σxσx⟩exterior and compare three conditions: (i) unitary Trotter evolution (baseline), (ii) mid-circuit measurement with reset on qubits near the horizon, and (iii) control measurement on distant qubits. Each circuit was executed with 16, 384 shots. The near-horizon measurement produces a (56. 5 ± 1. 9) % reduction in correlation contrast (95% CI from n = 5000 bootstrap resamples), while the control preserves (87. 8 ± 2. 1) % of baseline. Two ablation experiments constrain interpretation: removing the reset operation yields only a (2. 6 ± 1. 2) percentage point change, indicating that projective measurement—not state reset—drives the effect. Crucially, moving the measured subset 4 links away from the horizon collapses the reduction to (6. 5 ± 2. 3) %, yielding an 8. 2 ± 1. 4 ratio that demonstrates strong spatial localization. We additionally performed a flat-spacetime control with uniform coupling J (x) = Jmax on ibmₜorino (Heron r1, 133 qubits), obtaining a baseline contrast that collapses to a small residual near zero (C = − 0. 015, 95% CI − 0. 029, − 0. 002), confirming that the spatial structure arises from the engineered coupling profile rather than generic measurement artifacts. These results establish that mid-circuit measurement near an engineered coupling minimum preferentially disrupts correlations across that boundary, a signature qualitatively consistent with information-theoretic models of horizon physics.