  We study the heat statistics of a quantum Brownian motion described by the
Caldeira-Leggett model. By using the path integral approach, we introduce a
novel concept of the quantum heat functional along every pair of Feynman paths.
This approach has an advantage of improving our understanding about heat in
quantum systems. First, we demonstrate the microscopic reversibility of the
system by connecting the heat functional to the forward and its time-reversed
probabilities. Second, we analytically prove the quantum-classical
correspondence of the heat functional and their statistics, which allows us to
obtain better intuitions about the difference between classical and quantum
heat.
