Measurement induced dynamics and defect stabilization in spinor condensates*

Understanding system-reservoir dynamics in many-body physics is a new frontier. An external environment can be thought of as a `measurement reservoir' which extracts information about the quantum system. Weak (i.e. minimally destructive) measurements provide a time-resolved but noisy record of system evolution. In this talk, we propose using weak measurement and feedback to probe and manipulate spinor Bose-Einstein condensates, focusing on the trade-off between usable information obtained from measurement and the effect of measurement on the system (quantum backaction). As a prototype example, we consider the dynamics of a domain wall in a two-component BEC and show that quantum backaction due to measurement causes two primary effects: domain wall diffusion and overall heating. The system dynamics and signal-to-noise ratio depend on the choice of measurement observable. We describe a feedback protocol to create and stabilize a domain wall in the regime where domain walls are unstable, giving a prototype example of Hamiltonian engineering using measurement and feedback.