Coherent states with minimum Gini uncertainty for finite quantum systems

Abstract

Uncertainty relations $\Delta(\rho)\ge \eta_d$ in terms of the Gini index are studied. The `Gini uncertainty constant' $\eta_d$ is estimated numerically and compared to an upper bound $\tilde \eta_d\ge \eta_d$. It is shown that for large $d$ we get $\tilde \eta_d\approx \eta_d$. States $\ket{g}$ with minimum Gini uncertainty and displacement transformations are used to define coherent states $\ket{\alpha, \beta}_g$ (where $\alpha, \beta \in {\mathbb Z}_d$) with minimum Gini uncertainty ($\Delta[\ket{\alpha, \beta}_g\;_g\bra{\alpha, \beta}]\approx \eta_d$). The $\ket{\alpha, \beta}_g$ resolve the identity, and therefore an arbitrary state can be expanded in terms of them. This expansion is robust in the presence of noise.