Experimental Research Of Weak Measurement Based On Linear Optics

The mathematical system of quantum mechanics and its Copenhagen interpreta-tion have been confirmed in numerous experiments in physical fields since they were created.And measurement is one of the most important foundations in modern quantum mechanics.Quantum measurement has become more and more important in recently due to the demand of basic theory and practical application.In recent decades,great progress has been made in the research of quantum measurement.One of the most re-markable progress is the discovery and development of weak measurement and weak value.In the weak measurement,the coupling strength between the system and the pointer is very weak,and the system is post-selected into the finial state,so that the weak value of the observable can be obtained.Weak values have unusual properties,which can be manifested in the fact that they may be complex,and real part of weak val-ues may be far outside the range of the eigenvalue of the observable.Many theoretical and experimental studies have shown that weak values have very important applications in various fields of physics.In the field of quantum weak measurement,the following work has been accomplished in this paper:1.We experimentally realize the measurement of sequential weak values of three non-commuting Pauli observables in a photon system for the first time.The fact that one hardly disturbs the system when making weak measurements implies that non-commuting observables can be measured in succession and joint properties can be ex-tracted via so-called sequential weak values(SWVs).The measurement of SWVs ex-perimentally is thus of great interest from both fundamental and applicative points of view.Previously reported methods,however,can only make limited sequential weak measurements experimentally.It is still difficult to measure SWVs,either the real part or imaginary part,of non-commuting observables.We proposed how to measure SWVs of non-commuting Pauli observables and experimentally demonstrated for the first time the measurement of SWVs of three non-commuting observables with heralded single photons,which is impossible with previously reported methods.2.We experimentally demonstrate entanglement-assisted weak value amplifica-tion in a photonic system with genuine single photons.Weak value amplification has been used to enhance the sensitivity of a linear detector response to small interaction parameters.However,the generation of a large weak value gives rise to reduction in post-selection probability,which restricts the feasibility of the weak value amplifica-tion technique.Recently,theoretical works have shown that the use of entanglement can increase the efficiency of the weak value amplification method.We have proposed a concrete experimental scheme for the realization of entanglement-assisted weak value amplification,and demonstrated it experimentally.The results shown here also demon-strate the greater usefulness of entanglement,which can encourage further development in quantum measurement and metrology.