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The eavesdropping scheme proposed by Wójcik [Phys. Rev. Lett. 90,157901(2003)] on the ping-pong protocol [Phys. Rev. Lett. 89, 187902(2002)] is improved by constituting a new set of attack operations. The improved scheme has a zero eavesdropping-induced channel loss and produces perfect anticorrelation. Therefore, the eavesdropper Eve can safely attack all the transmitted bits and the eavesdropping information gain can always exceed the legitimate user's information gain in the whole domain of the quantum channel transmission efficiency η, i.e., [0,100%]. This means that the ping-pong protocol can be completely eavesdropped in its original version. But the improvement of the ping-pong protocol security produced by Wójcik is also suitable for our eavesdropping attack. . These QKD protocols are non-deterministic since the sender cannot determine the bit value that receiver will finally decode.Different from this kind of non-deterministic QKDs, the deterministic secure direct communication protocol is to transmit directly the secret messages without first generating QKD to encrypt them. This makes it very useful and usually desired, especially in some urgent time. However, the deterministic secure direct communication is more demanding on the security than non-deterministic QKDs. Therefore, only recently a few of deterministic secure direct protocols are proposed [21][22][23][24].One of them is the famous Boström-Felbinger protocol, or ping-pong protocol [22], which allows the generation of a deterministic key or even direct secret communication.In ping-pong protocol [22,25], Bob prepares two photons in the entangled state |Ψ + = (|0 |1 + |1 |0 )/ √ 2. He stores one photon (home photon) in his lab and sends Alice the other one (travel photon) via a quantum channel. After receiving the travel photon Alice randomly switches between the control mode and the message mode. In the control mode Alice measures the polarization of the travel photon first in the z-basis and then announces publicly the measurement result. After knowing Alice's announcement Bob also switches to the control mode to measure the home photon in the same basis as that Alice used. Then he compares both measurement results. They should be perfectly anticorrelated in the absence of Eve. Therefore, the appearance of identical results is

We study the quantum-state transfer ͑QST͒ of a class of tight-bonding Bloch electron systems with mirror symmetry by considering the mode entanglement. Some rigorous results are obtained to reveal the intrinsic relationship between the fidelity of QST and the mirror mode concurrence ͑MMC͒, which is defined to measure the mode entanglement with a certain spatial symmetry and is just the overlap of a proper wave function with its mirror image. A complementarity is discovered as the maximum fidelity is accompanied by a minimum of the MMC. At the instant that is just half of the characteristic time required to accomplish a perfect QST, the MMC can reach its maximum value of 1. A large class of perfect QST models with a certain spectral structure is discovered to support our analytical results.