In this work we investigate, against common intuition, how a thermal bath can induce localization in an interacting many-body system with ergodic eigenstates. I will give a brief overview of some related ideas and models in which a bath impedes thermalization of the system. In our case, this needs reconsideration of how to describe the Markovian dynamics of a quantum system in contact with a bath. Then I’ll show how we can apply this idea to Dynamic Nuclear Polarization (DNP), an experimental protocol used in NMR applications. The setup is a quantum-interacting spin system subject to an external drive and coupled to a thermal bath of vibrational modes, uncorrelated for different spins. The many-body eigenstates of the spin system being ergodic (satisfying the eigenstate thermalization hypothesis), one expects that dephasing renders the nonequilibrium stationary state thermal with a drive-dependent temperature, a highly-coveted regime called thermal mixing in DNP. We show that a sufficiently strong coupling to the bath may instead effectively localize the spins due to a many-body quantum Zeno effect. The strong coupling is here simply realized by increasing temperature, which enhances the dynamics of the vibrational bath modes. While the analysis and setting is different, this scenario is similar to the recent measurement-induced entanglement transition in schematic models. Going beyond the conventional weak-coupling secular approximation to the system-bath dynamics is required to capture this phenomenon. In the DNP context, our results provide an explanation of the breakdown of the thermal mixing regime experimentally observed above 4-5 K.

IPhT