Calorimetric Signature of Quantum Measurement: A Record-Formation Heat Bound and Differential Microcalorimetry Test

We propose that quantum measurement is a boundary event: a physically identifiable, irreversible transition in which a reversible system/pointer correlation is forced across an operational irreversibility threshold into objective classical record stabilization. We formulate a three-stage taxonomy separating reversible premeasurement (Stage 1), irreversible record formation (Stage 2, the boundary event), and memory reset (Stage 3), and identify the stage at which a Landauer-scale heat bound applies. Under explicit operational conditions (C1–C6) in the uncontrolled-decoherence regime, the record-formation channel must dissipate at least k_B T ln 2 of heat per bit of classical mutual information I(X;Y). We propose a circuit-QED differential microcalorimetry experiment with matched ON/OFF branches that share identical premeasurement pulses and routing losses, differing only in whether an objective record is stabilized. The measurand is the differential deposited energy ΔQ ≡ Q_ON − Q_OFF, which isolates record-formation dissipation from common-mode backgrounds. The primary deep-quantum demonstration targets the temporal coincidence of heat onset and reversibility loss via a reversal-delay sweep (Control 3), providing a distinctive boundary-event signature even when ΔQ >> k_B T ln 2. Near-floor residual tests (r ≡ ΔQ − k_B T ln 2 · I(X;Y)) require lower-energy pointer implementations or elevated operating temperatures and are presented as a concrete roadmap. The bound is falsified if r is negative at high statistical significance under verified conditions.