Determination of weak values of quantum operators using only strong measurements

TL;DR

This paper demonstrates that weak values of quantum operators can be obtained solely through strong measurements, challenging the notion that weak measurements are necessary for their determination.

Contribution

It shows that weak values are properties of operators linked with pre- and post-selection, accessible via expectation values from strong measurements, and provides specific examples including momentum and neutron spin.

Findings

Weak values can be derived from expectation values of density, flux, and commutator operators.

Strong measurements suffice to determine both real and imaginary parts of weak values.

Application to neutron interferometry confirms the practical feasibility.

Abstract

Weak values have been shown to be helpful especially when considering them as the outcomes of weak measurements. In this paper we show that in principle, the real and imaginary parts of the weak value of any operator may be elucidated from expectation values of suitably defined density, flux and hermitian commutator operators. Expectation values are the outcomes of strong (projective) measurements implying that weak values are general properties of operators in association with pre- and post-selection and they need not be preferentially associated with weak measurements. They should be considered as an important measurable property which provides added information as compared with the "standard" diagonal expectation value of an operator. As a first specific example we consider the determination of the real and imaginary parts of the weak value of the momentum operator employing projective time of flight experiments. Then the results are analyzed from the point of view of Bohmian mechanics. Finally we consider recent neutron interferometry experiments used to determine the weak values of the neutron spin.