Two-axis spin squeezing of two-component BEC via a continuous driving*

In two-component BEC, the one-axis twisting Hamiltonian leads to spin squeezing with the limitation that scales with the number of atoms as $N^{-\frac{2}{3}}$. We propose a scheme to transform the one-axis twisting Hamiltonian into a two-axis twisting Hamiltonian, resulting in enhanced spin squeezing $\propto N^{-1}$ approaching the Heisenberg limit. Instead of pulse sequences, only one continuous driving field is required to realizing such transforming, thus the scheme is promising for experiment realizations, to an one-axis twisting Hamiltonian. Quantum information processing and quantum metrology may benefit from this method in the future. Besides, our scheme is spin number in- dependent and needs a shorter evolution time compared with [1]. \\[4pt] [1] C. Shen and L. M. Duan, Phys. Rev. A \textbf{87}, 051801 (2013).