Quantum trajectories without quantum jumps

Abstract

Superconducting qubits have provided a fertile landscape for pioneering work examining experimental quantum trajectories. Here, continuous monitoring of a quantum system's environment can be used to unravel individual quantum trajectories of the open system evolution. Many fascinating extensions of these trajectories have been explored, including quantum state smoothing, retrodiction, parameter estimation, connections to thermodynamics, topological transitions, quantum feedback, and much more. Resisting the temptation to discuss all of these topics at breakneck pace, this talk will instead focus on a simple case: a quantum system interacting with its environment via radiative decay. This is typically and ultimately characterized by quantum jumps of the system to a lower energy level. What happens before these quantum jumps occur? Here, in the absence of quantum jumps, the dissipative interaction results in coherent, yet non-unitary evolution described by an effective non-Hermitian Hamiltonian. I will survey our recent work that explores the rich landscape of these non-Hermitian dynamics highlighting connections to quantum measurement dynamics along the way.