Topological Transitions in Quantum Jump Dynamics: Hidden Exceptional Points

Complex spectra of dissipative quantum systems may exhibit degeneracies known as exceptional points (EPs). At these points the systems’ dynamics may undergo a drastic change. Phenomena associated with EPs and their applications have been extensively studied in relation to various experimental platforms, including, i.a., the superconducting circuits and cold atoms. While most of the studies focus on EPs appearing due to the variation of the system’s parameters, I discuss EPs emerging in the full counting statistics of the system and the underlying topological nature of observed quantum jump dynamics. As a particular example, we consider a monitored V-shaped three level system and find multiple EPs in the Lindbladian eigenvalues considered as functions of a counting field. These EPs signify transitions between different topological classes which are rigorously characterized in terms of the braid theory. We identify dynamical observables affected by these transitions and demonstrate how the underlying topology can be recovered from experimentally measured quantum jump distributions. Additionally, we establish a duality between certain EPs in the Lindbladian with regard to the counting field - this allows for an experimental observation of the EP transitions, normally hidden by the Liouvillian dynamics of the system, without applying postselection schemes.