Entanglement and squeezing of a four-qubit system via two-axis counter twisting Hamiltonian

We study the entanglement and squeezing properties of a spin system of 4 qubits under the influence of the two-axis counter twisting Hamiltonian. Our initial spin state is a coherent one in the z-direction, which evolves in time. We choose the squeezing parameters given by Wineland and Kitagawa as the criteria of spin squeezing. The criterion of pair-wise entanglement is chosen to be the concurrence and that of the bipartite entanglement, the linear entropy. We will study and plot the time dependence of the squeezing and entanglement parameters and also determine the time domains in which squeezing and entanglement properties can or can not exist simultaneously.