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

We propose that the transition from reversible quantum correlation to an objective classical record is a thermodynamically irreversible process with a quantifiable heat signature. We formulate a three-stage taxonomy separating reversible premeasurement, irreversible record formation, and memory reset, and derive a conditional record-formation heat bound: under explicit operational conditions (C1 to C6) in the uncontrolled-decoherence regime (no work extraction/coherence-recovery channel), the irreversible record-formation channel must dissipate at least kB T ln 2 of heat per bit of classical information created, quantified by the mutual information I(X;Y) between a prepared classical label X and the recorded outcome Y. Using an explicit system/pointer/bath model, we identify the precise stage at which this Landauer cost is paid: not during unitary premeasurement coupling, but during irreversible environmental coupling, when the pointer becomes entangled with N >> 1 environmental degrees of freedom and the record is stabilized. We design a circuit-QED differential microcalorimetry experiment using superconducting qubits and nanocalorimeters (TES or SNS nanobolometer class). The protocol employs 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 per-shot differential deposited energy ΔQ ≡ Q_ON - Q_OFF, which isolates the record-formation contribution. Four primary controls (ground-state baseline, measurement-strength scaling, reversal-delay timing sweep, and prior-variation) discriminate from systematic effects. Sensitivity analysis using demonstrated nanobolometer performance shows detection is feasible with N ~ 2 × 10^9 to 8 × 10^9 ON/OFF pairs at 10 mK for Landauer-scale residual tests at SNR ~ 10 (for σ_Q ≈ 0.32 to 0.6 zJ and ΔQ_target ≈ 9.57×10^-5 zJ). The bound is falsified if the observed residual ΔQ - kB T ln 2 · I(X;Y) falls statistically below zero.