Assessing the validity of the thermodynamic uncertainty relation in quantum systems

We examine the so-called thermodynamic uncertainty relation (TUR), a cost-precision trade-off relationship in transport systems. Based on the fluctuation symmetry, we derive a condition for invalidating the TUR for general nonequilibrium (classical and quantum) systems. We find that the first nonzero contribution to the TUR beyond equilibrium, given in terms of nonlinear transport coefficients, can be positive or negative, thus affirming or violating the TUR depending on the details of the system. We exemplify our results for noninteracting quantum systems by expressing the thermodynamic uncertainty relation in the language of the transmission function. We demonstrate that quantum coherent systems that do not follow a population Markovian master equation, e.g., by supporting high-order tunneling processes or relying on coherences, violate the TUR.