arXiv subjects
Publications and source records attributed to Zhan-jun Zhang.
We show that all the correlations defined by K. Modi et al [Phys. Rev. Lett. {\bf 104}, 080501 (2010)] except for the total mutual information should be redefined so that some physical quantities (e.g., the accessible maximal classical correlation and the resultant exact quantum discord) are right.
We present two quantum information splitting schemes using respectively tripartite GHZ and asymmetric W states as quantum channels. We show that, if the secret state is chosen from a special ensemble and known to the sender (Alice), then she can split and distribute it to the receivers Bob and Charlie by performing only a single-qubit measurement and broadcasting an one-cbit message. It is clear that no other schemes could possibly achieve the same goal with simpler measurement and less classical communication. In comparison, existing schemes work for arbitrary quantum states which need not be known to Alice, however she is required to perform a two-qubit Bell measurement and communicate a two-cbit message. Hence there is a trade off between flexibility and measurement complexity plus classical resource. In situations where our schemes are applicable, they will greatly reduce the measurement complexity and at the same time cut the communication overhead by one half.
Recently, several similar protocols[J. Opt. B 4 (2002) 380; Phys. Lett. A 316 (2003) 159; Phys. Lett. A 355 (2006) 285; Phys. Lett. A 336 (2005) 317] for remotely preparing a class of multi-qubit states (i.e, $α|0 ... 0>+β|1... 1>$) are proposed, respectively. In this paper, by applying the controlled-not (CNOT) gate, a new simple protocol is proposed for remotely preparing such class of states. Compared to the previous protocols, both classical communication cost and required quantum entanglement in our protocol are remarkably reduced. Moreover, the difficulty of identifying some quantum states in our protocol is also degraded. Hence our protocol is more economical and feasible.
Recently Z. S. Zhang et al [Phys. Lett. A 356(2006)199] have proposed an one-way quantum identity authentication scheme and claimed that it can verify the user's identity and update securely the initial authentication key for reuse.
Recently Xia and Song [Phys. Lett. A (In press)] have proposed a controlled quantum secure direct communication (CQSDC) protocol. They claimed that in their protocol only with the help of the controller Charlie, the receiver Alice can successfully extract the secret message from the sender Bob. In this letter, first we will show that within their protocol the controller Charlie's role can be excluded due to their unreasonable design. We then revise the Xia-Song CQSDC protocol such that its original advantages are retained and the CQSDC can be really realized.
This paper includes two comments. The first one is a comment on 'Teleportation of two quNit entanglement: Exploiting local resources'. Two different efficient methods are presented to modify some details of N. Ba An's protocol, so that teleportation of two quNit entanglement can be successfully achieved in terms of the revised N. Ba An's protocol. The second one is a comment on 'Reply to Yang et al.'s comment'.
We propose a protocol ${\cal D}_n$ for faithfully teleporting an arbitrary $n$-qudit state with the tensor product state (TPS) of $n$ generalized Bell states (GBSs) as the quantum channel. We also put forward explicit protocol ${\cal D}'_n$ and ${\cal D}''_n$ for faithfully teleporting an arbitrary $n$-qudit state with two classes of $2n$-qudit GESs as the quantum channel, where the GESs are a kind of genuine entangled states we construct and can not be reducible to the TPS of $n$ GBSs.
A three-party scheme for securely sharing an arbitrary unknown single-qutrit state is presented. Using a general Greenberger-Horne-Zeilinger (GHZ) state as the quantum channel among the three parties, the quantum information (i.e., the qutrit state) from the sender can be split in such a way that the information can be recovered if and only if both receivers collaborate. Moreover, the generation of the scheme to multi-party case is also sketched.
Two protocols of quantum direct communication with authentication [Phys. Rev. A {\bf 73}, 042305 (2006)] are recently proposed by Lee, Lim and Yang. In this paper we will show that in the two protocols the authenticator Trent should be prevented from knowing the secret message of communication. The first protocol can be eavesdropped by Trent using the the intercept-measure-resend attack, while the second protocol can be eavesdropped by Trent using single-qubit measurement. To fix these leaks, I revise the original versions of the protocols by using the Pauli-Z operation $σ_z$ instead of the original bit-flip operation $X$. As a consequence, the protocol securities are improved.
The security proof of the ping-pong protocol is wrong.
We analyzed the security of the multiparty quantum secret sharing (MQSS) protocol recently proposed by Zhang, Li and Man [Phys. Rev. A \textbf{71}, 044301 (2005)] and found that this protocol is secure for any other eavesdropper except for the agent Bob who prepares the quantum signals as he can attack the quantum communication with a Trojan horse. That is, Bob replaces the single-photon signal with a multi-photon one and the other agent Charlie cannot find this cheating as she does not measure the photons before they runs back from the boss Alice, which reveals that this MQSS protocol is not secure for Bob. Finally, we present a possible improvement of the MQSS protocol security with two single-photon measurements and six unitary operations.
I show a scheme which allows a perfect transfer of an unknown single-qubit atomic state from one atom to another by letting two atoms interact simultaneously with a cavity QED. During the interaction between atom and cavity, the cavity is only virtually excited and accordingly the scheme is insensitive to the cavity field states and cavity decay. Based on this scheme, a network for transfer of an arbitrary single-qubit atomic state between atoms is engineered. Then the scheme is generalized to perfectly transfer an arbitrary 2-qubit atomic state and accordingly a network for transfer of an arbitrary 2-qubit atomic state is designed. At last, it is proven that the schemes can be generalized to an arbitrary $n(n\ge 3)$-qubit atomic state transfer case and a corresponding network is also proposed.
We present a general idea to construct methods for multi-qubit quantum teleportation between two remote parties with control of many agents in the network. Our methods seem to be much simpler than the existing method proposed recently (Phys. Rev. A {\bf 70}, 022329(2004)). We then demonstrate our idea by using several different protocols of quantum key distribution, including Ekert 91 and the deterministic secure communication protocol raised by Deng and Long.
First, I show explicitly a scheme to {\it faithfully} and {\it deterministically} teleport an arbitrary 2-qubit state from Alice to Bob. In this scheme two same Bell states are sufficient for use. Bob can recover the 2-qubit state by performing at most 4 single-qubit unitary operations conditioned on Alice's 4-bit classical public message corresponding to her two Bell-state measurement outcomes. Then I generalize the 2-qubit teleportation scheme to an aribitrary $N(N\ge 3)$-qubit state teleportation case by using $N$ same Bell states. In the generalized scheme, Alice only needs to identify $N$ Bell states after quantum swapping and then publish her measurement outcomes ($2N$-bit classical message). Conditioned on Alice's $2N$-bit classical message, Bob only needs to perform at most $2N$ single-qubit unitary operations to {\it fully} recover the arbitrary state. By comparing with the newest relevant work [Phys. Rev. A{\bf 71}, 032303(2005)], the advantages of the present schemes are revealed, respectively.
Based on a quantum secure direct communication (QSDC) protocol [Phys. Rev. A69(04)052319], we propose a $(n,n)$-threshold scheme of multiparty quantum secret sharing of classical messages (QSSCM) using only single photons. We take advantage of this multiparty QSSCM scheme to establish a scheme of multiparty secret sharing of quantum information (SSQI), in which only all quantum information receivers collaborate can the original qubit be reconstructed. A general idea is also proposed for constructing multiparty SSQI schemes from any QSSCM scheme.
The eavesdropping scheme proposed by Wójcik [Phys. Rev. Lett. {\bf 90},157901(2003)] on the ping-pong protocol [Phys. Rev. Lett. {\bf 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.
We present a subtle idea to economically improve message-unilaterally-transmitted quantum secure direct communication (QSDC) protocols to realize two-way secure direct communication.