Operational quasiprobability in quantum thermodynamics: Work extraction by coherence and nonjoint measurability

This is the authors' abstract. We don't add key points for this paper.

We employ the operational quasiprobability (OQ) as a work distribution, which reproduces the Jarzynski equality and yields the average work consistent with the classical definition. The OQ distribution can be implemented through two simple experimental settings: the end-point measurement and the two-point measurement. Using this framework, we demonstrate the explicit contribution of coherence to the work, which can be formulated by the second-law-type relation. In a two-level system, we show that nonjoint measurability, a generalized notion of measurement incompatibility, can increase the amount of extractable work beyond the classical bound imposed by jointly measurable measurements. We further prove that the real part of Kirkwood-Dirac quasiprobability (KDQ) and the OQ are equivalent in two-level systems, and they are non-negative for binary unbiased measurements if and only if the measurements are jointly measurable. In a three-level nitrogen-vacancy center system, the OQ and the KDQ exhibit different amounts of negativities while enabling the same work extraction, implying that the magnitude of negativity is not a faithful indicator of nonclassical work. These results highlight that coherence and nonjoint measurability play fundamental roles in the enhancement of work.