Measurement induced phase transition in ground states*

An external observer can have a profound impact on the quantum state that it is observing. Recent studies of random quantum circuits have shown that if the object of observation is a large many-body system, then mere observation can induce a phase transition in the large scale quantum correlations of the system. In this talk I will argue that observing a quantum ground state can similarly lead to a phase transition in the structure of long range correlations in the state. As a concrete example I will consider the impact of weak measurement of the density of a one dimensional quantum liquid applied for a finite time.