  Three entanglement concentration protocols (ECPs) are proposed. The first ECP
and a modified version of that are shown to be useful for the creation of
maximally entangled cat and GHZ-like states from their non-maximally entangled
counterparts. The last two ECPs are designed for the creation of maximally
entangled $(n+1)$-qubit state
$\frac{1}{\sqrt{2}}\left(|\Psi_{0}\rangle|0\rangle+|\Psi_{1}\rangle|1\rangle\right)$
from the partially entangled $(n+1)$-qubit normalized state
$\alpha|\Psi_{0}\rangle|0\rangle+\beta|\Psi_{1}\rangle|1\rangle$, where
$\langle\Psi_{1}|\Psi_{0}\rangle=0$ and $|\alpha|\neq\frac{1}{\sqrt{2}}$. It is
also shown that W, GHZ, GHZ-like, Bell and cat states and specific states from
the 9 SLOCC-nonequivalent families of 4-qubit entangled states can be expressed
as
$\frac{1}{\sqrt{2}}\left(|\Psi_{0}\rangle|0\rangle+|\Psi_{1}\rangle|1\rangle\right)$
and consequently the last two ECPs proposed here are applicable to all these
states. Quantum circuits for implementation of the proposed ECPs are provided
and it is shown that the proposed ECPs can be realized using linear optics.
Efficiency of the ECPs are studied using a recently introduced quantitative
measure (Phys. Rev. A $\textbf{85}$, 012307 (2012)). Limitations of the measure
are also reported.
