= Riccardo Rattazzi
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<Riccardo Rattazzi> developed a path-integral account of <quantum mechanics> that connects interference, operator evolution and statistical methods. His notes derive the <path integral> from quantum time evolution, work out the free-particle propagator and treat Gaussian fluctuations.<The Path Integral approach to Quantum Mechanics by Riccardo Rattazzi>[Sections1.1–1.3 and2.2: derivation, free particle and Euclidean methods]{ref}
The weight $e^{iS/\hbar}$, with $S$ the <action functional>, is an amplitude with a phase, not a classical probability assigned to each path. Combining amplitudes before taking probabilities produces interference. Analytic continuation to Euclidean time then connects suitable quantum calculations with statistical-mechanical formulations, under the required convergence and boundary assumptions.
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