One Measurement, Many Fronts in Kitaev and Cluster Chains

arXiv:2611.10912v1 Announce Type: new Abstract: A projective measurement of one site in the ground state of a quantum chain disturbs the chain in two ways: learning the outcome shifts distant expectation values at once, through ground-state correlations, and the measurement erases the correlations between the measured site and the rest. Both changes travel outward. We solve this problem exactly for the Kitaev chain, the cluster chain in a transverse field, and the Kitaev chain with power-law couplings, and we find that far from the measured site every quadratic observable responds through a front. Where the front is and how fast it broadens depend only on the quasiparticle dispersion.