Special CPM Seminar

Measurements conspire nonlocally to restructure critical quantum states

Samuel Garratt

UC Berkely

I will discuss the effects of local measurements on critical quantum ground states. In critical states there are algebraic correlations between local observables and, as a consequence, local measurements can have highly nonlocal effects. This raises the possibility for measured-induced collective phenomena that do not involve dynamics. These correspond to the restructuring of many-body quantum states, and are associated with changes in the scaling of correlations and of the entanglement entropy. I will explain how this behavior can be captured within a field theory through the standard quantum-classical mapping underlying the theory of quantum phase transitions, and highlight the connection to studies of boundary criticality. The phenomena I will describe are robust to decoherence, which is unavoidable in experiment, although a post-selection problem poses a barrier to their direct observation. I will show that resource-efficient signatures are instead to be found in cross-correlations between experimental measurement results and simulations on classical computers.