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

We propose that the transition from quantum correlation to objective classical record is a thermodynamically irreversible process, and derive a bound: the irreversible record-formation channel must dissipate at least k_B T ln 2 of heat per bit of classical information created. 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 amplification when the pointer becomes entangled with N >> 1 environmental degrees of freedom. We formulate a record-formation heat bound and propose a circuit-QED differential calorimetry experiment using superconducting qubits and nanocalorimeters (TES or SNS nanobolometer class). The protocol compares heat dissipation between record-forming measurements and matched controls, yielding a differential observable ΔQ that suppresses dominant readout-chain backgrounds. Three control experiments (constant-preparation null test, measurement-strength scaling, and reversal-delay timing sweep) provide discrimination from systematic effects. Sensitivity analysis using demonstrated nanobolometer performance shows detection is feasible with N ~ 10^9 repetitions at 10 mK, achieving SNR ≳ 10. The bound is falsified if the observed slope of ΔQ versus classical information I(X;Y) falls statistically below k_B T ln 2.