# Concurrence and three tangle

Tags:
1. Oct 21, 2016

### munirah

Good day,

May anyone help me to confirm the formula use for three tangle using concurrence.

three tangle,

$$\tau=\tau_{A(BC)}-\tau_{AB}-\tau_{AC}$$

and it can be related to concurrence

$$\tau=C^2_{A(BC)}-C^2_{AB}-C^2_{AC}$$

and I used formula for C is

$$C^2=2-(Tr\rho^2_1+Tr\rho^2_2)$$ where $$\rho$$ is partial trace.
[FONT=Georgia, Times New Roman, Times, serif]
When I calculate the GHZ state, I get zero. It suppose
[/FONT]$$\tau>0$$ for GHZ state and $$\tau=0$$ for W state
[FONT=Georgia, Times New Roman, Times, serif]
May I know, what it mean by the $$\tau$$ here. Please help me.

And How I can calculated the density matrix of the state using three tangle. May anyone show me an example. I'm really stuck. Please help me.

Thank you.
[/FONT]

2. Oct 26, 2016