Yi Zhang A general quantum strategy unifies quantum measurements 12/31/2021
Title: A general quantum strategy unifies quantum measurements
Speaker: Prof. Yi Zhang, Peking University
Time: Dec. 31 (Friday), 10:00
Place: Rm M830, IOP-CAS

 Quantum measurements are our eyes to the microscopic world of quantum systems consisting of a multitude of degrees of freedom. However, the intrinsic uncertainty of quantum measurements and the exponentially large Hilbert space pose natural barriers to simple interpretations of the measurement outcomes. We propose a nonlinear "measurement energy" based upon the ensemble of available results from quantum measurements and a general gradient-descent approach of effective quantum Hamiltonians to extract the most probable states (maximum likelihood estimates), thus offering a unified interpretation that gets the most out of the quantum measurements as well as reconcile between different platforms. We showcase the versatility and accuracy of our perspective on random long-range fermion models and disordered Kitaev quantum spin liquid models, where smoking-gun signatures are lacking. The measurement energy also leads to our so-call "quantum constraints," which determine how close specific operator expectation values are to physically realizable by a quantum many-body state and obtainable via sampling then machine learning on a large number of quantum-state samples. With these quantum constraints, the search for ground-state properties of quantum many-body systems equates to simple classical constrained minimizations.