Dense Coding in Two Kinds of Two-Qubit Spin Squeezing Model

We investigate the effects of spin squeezing interaction, external magnetic field and temperature on dense coding capacity properties in two kinds of two-qubit spin squeezing model: one-axis twisting model (OATM) and two-axis countertwisting model (TACM). To the OATM, it is found that the value of dense coding capacity χ is larger than 1 in the region of larger values of Ω(external magnetic filed) and μ(squeezing interaction) parameters space, while in the region of lower values of Ω and μ parameters space, χ is always less than 1 and not valid for dense coding. With increasing temperature T the dense coding capacity is decayed, and one can carry out the valid dense coding in the lower T region through tuning Ω. To the TACM, it is found that the value of χ is promoted with increasing the squeezing parameter γ. Through increasing γ, χ finally reached to one stable value, which is always larger than 1 whatever value of Ω is. The valid dense coding capacity χ can be enhanced through tuning the parameter Ω or γ, but it is decreased with increasing T. Our results show that with proper enhancing the parameter Ω or γ it is easy to carry out the valid dense coding (χ > 1) and the optimal dense coding (χ = 2) when the system in TACM.