Improving teleportation of continuous variables by local operations

We study a continuous-variable (CV) teleportation protocol based on a shared entangled state produced by the quantum-nondemolition (QND) interaction of two vacuum states. The scheme utilizes the QND interaction or an unbalanced beam splitter in the Bell measurement. It is shown that in the nonunity gain regime the signal transfer coefficient can be enhanced while the conditional variance product remains preserved by applying appropriate local squeezing operation on sender’s part of the shared entangled state. In the unity gain regime, it is demonstrated that the fidelity of teleportation can be increased with the help of the local squeezing operations on parts of the shared entangled state that effectively convert our scheme to the standard CV teleportation scheme. Further, it is proved analytically that such a choice of the local symplectic operations minimizes the noise by which the mean number of photons in the input state is increased during the teleportation. Finally, our analysis reveals that the local symplectic operation on sender’s side can be integrated into the Bell measurement if the interaction constant of the interaction in the Bell measurement can be adjusted properly.

Figure 1

Schematic of the CV teleportation using the QND interaction. A bipartite entangled state produced by the QND interaction (1) of two vacuum states ${\mid 0⟩}_A$ and ${\mid 0⟩}_B$ is shared by Alice and Bob. ${\mid \alpha ⟩}_{\mathrm{in}}$, an unknown input coherent state; ${\rho }_{\mathrm{out}}$, output state; $S_A$ and $S_B$, auxiliary squeezing operations allowing to improve the quality of teleportation; $R$, the QND interaction or an unbalanced BS; $G_x$, $G_p$, electronic gains for the transformation from the classical measurement results ${\overline{x}}_{\mathrm{in}}$ and ${\overline{p}}_A$ to Bob’s output system.