Universal Lower Bound on Quantum Measurement Timescales

The quantum measurement problem the tension between unitary Schrödinger evolution and the projection postulate has been with us since the early days of quantum theory. Here we derive a lower bound on the time required for any quantum measurement, treating the measurement as quantum channel discrimination carried out by the environment. The resulting bound, \tau_{\mathcal{M}} \ge \frac{\ln N}{2\pi\gamma}, relates the measurement time \tau_{\mathcal{M}} to the number of distinguishable outcomes N and the system-environment coupling strength \gamma. It follows from combining a finite channel-capacity limit on information transfer with the thermodynamic cost of erasing information, as set by Landauer's principle. The bound explains why measurements look instantaneous at macroscopic scales while still being bounded away from zero, gives a timescale for the onset of classical objectivity under quantum Darwinism, and yields concrete, testable predictions for weak-measurement experiments in cavity quantum electrodynamics and superconducting circuits.