Quantum-coherence quantifiers based on the Tsallis relative $\alpha$ entropies

The concept of coherence is one of cornerstones in physics. The development of quantum information science has lead to renewed interest in properly approaching the coherence at the quantum level. Various measures could be proposed to quantify coherence of a quantum state with respect to the prescribed orthonormal basis. To be a proper measure of coherence, each candidate should enjoy certain properties. It seems that the monotonicity property plays a crucial role here. Indeed, there is known an intuitive measure of coherence that does not share this condition. We study coherence measures induced by quantum divergences of the Tsallis type. Basic properties of the considered coherence quantifiers are derived. Tradeoff relations between coherence and mixedness are examined. The property of monotonicity under incoherent selective measurements has to be reformulated. The proposed formulation can naturally be treated as a parametric extension of its standard form. Finally, two coherence measures quadratic in moduli of matrix elements are compared from the monotonicity viewpoint.

Figure 1

Maximal values of $C_{\alpha }\left(\widehat{\omega }\right)$ versus $u$ are shown by a dashed line for $\alpha =1$, by a solid line for $\alpha =2$, by a dash-dotted line for $\alpha =3$, and by a dotted line for $\alpha =4$.

Figure 2

The minimal and maximal values of the sum $C_2\left(\widehat{\omega }\right)+\mathrm{M}\left(\widehat{\omega }\right)$ as functions of $u$.