A new entanglement measure: D-concurrence

otherwise it is entangled or inseparable. Then a question arises: How to detect whether a state is entangled or not? If ρ is entangled, how to quantify the degree of its entanglement? To answer these two questions, we need to introduce some measures of entanglement to quantify the degree of entanglement. The entanglement measure for a state is zero iff the state is separable, and the bigger is the entanglement measure, then more entanglement is the state. One of the most famous measures of entanglement is the concurrence [5] of two-qubit system. The concurrence of a pure two-qubit state ψ is given by