Uncertainty Inequality for the Entanglement of Both Two-rebits and Two-qubits States

We assume that both the concurrence C_r of a two-rebits state and the concurrence C_q of the usual two-qubits states are represented by hermitian operators (observables). We calculate the respective uncertainty ΔC_r and the uncertainty ΔC_q measured both as the standard deviation . We make the strictly mathematical assumption that there exists a canonical conjugate variable (called ξ) to the concurrence (C) such that both quantities satisfy a Robertson’s [1] uncertainty inequality of the form ( {left(Delta Aright)}^2{left(Delta Bright)}^2>{left|frac{1}{2}leftlangle right[A,Bleft]rightrangle right|}^2 ). From such inequality we impose bounds for both uncertainties Δξ_r and Δξ_q.