Direct Observation of Hardy's Paradox by Weak Measurement

Abstract

In quantum mechanics, it is difficult to decide a value of a physical quantity in the middle of a time evolution due to the impossibility of measurement without disturbance. Hardy's paradox is one of the most striking examples, against which one may point out we cannot actually verify such a counterfactual statement. This criticism has not always been valid, after Aharonov et al. proposed weak measurement, which gives us a protocol for measurement without disturbance on a time evolution. Actually, we performed weak measurement on Hardy's paradox and observed that our measurement apparatus gave us the paradoxical values. In this article, we introduce weak measurement and show our experimental result of weak measurement on Hardy's paradox.