Weak values and the past of a quantum particle

We investigate four key issues with using a nonzero weak value of the spatial projection operator to infer past path an individual quantum particle. First, we note that measurements disturb system, so any approach relying on such perturbation determine location particle describes state disturbed not hypothetical undisturbed system. Secondly, even assuming no disturbance, there is reason associate non-zero containing classical idea `particle presence'. Thirdly, values are only measurable over ensembles, and properties particles from them problematic. Finally, approaches do provide information beyond standard mechanics (and modes supporting experiment). know experiment testable consequences demonstrates connection between presence values.