Kondo-Zeno crossover in the dynamics of a monitored quantum dot

We study the dynamics of a quantum dot coupled to a metallic bath and subject to continuous monitoring of its charge density. The dynamics averaged over measurement noise is described by a dissipative Anderson impurity model with local Markovian dephasing, that we solve using an extension of the Non-Crossing Approximation in the vectorized Hilbert space. We show that the decay time scale of an initially polarised spin which is suddenly coupled to the bath and to the monitoring protocol displays a crossover from Kondo screening, with a lifetime controlled by interactions, to Quantum Zeno effect, with a lifetime which decreases with bare dissipation as the dephasing or monitoring rate is increased. Using a Schrieffer-Wolff transformation on the Lindbladian we derive an effective model for the long-time dynamics which is described at weak dissipation by a non-Hermitian Kondo model with complex-valued spin-spin exchange. As the dephasing is increased heating due to doublon production takes over and control the spin decay.