Direct measurement methods of density matrix of an entangled quantum state

Abstract

In general, the state of a quantum system represented by the density operator and its determination is a fundamental problem in quantum theory. In this study, two theoretical methods such as using postselected measurement characterized by modular value and sequential measurements of triple products of complementary observables to direct measurement of matrix elements of density operator of a two photon entangled quantum state are introduced. The similarity and possible feasibilities of those two methods are discussed by considering the previous theoretical and experimental works.