Time: July, 12 (Wednesday), 10:00
Place: Rm 401, 7th Buidling, UCAS Zhongguancun Campus (中关村东路80号7号楼401)

Speaker: Prof. Bi, Zhen (Penn State University)

Abstract:

In condensed matter physics, we usually think about quantum phases and phase transitions in the context of equilibrium many-body system. In this talk, we consider a slightly different setup. We will consider preparing quantum phases and phase transitions with shallow quantum circuit and measurements in quantum simulators. First, I will talk about ways one can prepare some high-entangled quantum states, including topological order, symmetry-breaking cat state, etc., by measuring a so-called resource state. Then I will show that with post-selection one can tune a phase transition between certain quantum states by changing a continuous parameter in the measurements. This measurement-prepared quantum critical state corresponds to the so-called conformal quantum critical points where the equal-time correlators exhibit spatial conformal invariance. This establishes an exact correspondence between the measurement-prepared critical states and conformal field theories of a range of critical spin models, including familiar Ising models and gauge theories. Without post-selection, we can show the correspondence between the ensemble of quantum states prepared by measurements and the ensemble of the ferromagnetic random bond ising model along the special path called Nishimori line. Our findings suggest a novel mechanism in which a quantum critical wavefunction emerges, providing new ways to study quantum phases and conformal quantum critical points.