Zhang Zhan-Jun

Deterministic Secure Direct Communication by Using Swapping Quantum Entanglement and Local Unitary Operations

A deterministic direct quantum communication protocol is proposed by using swapping quantum entanglement and local unitary operations. The present protocol is secure for the proof of the security of the present scheme, the same as that in the two-step protocol [Phys. Rev. A 68 (2003) 042317]. Additionally, the advantages and disadvantages of the present protocol is also discussed.

Quantum Dialogue Revisited

An entanglement-based quantum dialogue protocol [Phys. Lett. A 328 (2004) 6] is proven to be insecure: that is, in the protocol an eavesdropper can steal the secret messages without being detected provided that he/she adopts the intercept-and-resend attack strategy. We modify the protocol, i.e. in the control mode, by introducing and randomly choosing two sets of measuring basis: the intercept-and-resend attack can be accordingly detected. Hence, within the present version two users can securely and simultaneously exchange their secret messages.

Revisiting quantum secure direct communication with W state

The quantum secure direct communication protocol recently proposed by Cao and Song [Chin, Phys. Lett. 23 (2006) 290] (i.e., the C-S QSDC protocol) is revisited. A security leak is pointed out. Taking advantage of this leak, an eavesdropper may adopt the intercept-measure-resend strategy to attack the quantum channel such that in the C-S QSDC protocol the secret message can be completely eavesdropped. To fix the leak, the original version of the C-S QSDC protocol is revised. As a consequence, the security is improved and assured at least in the ideal case of an ideal quantum channel.

Assisted Cloning and Orthogonal Complementing of an Arbitrary Unknown Two-Qubit Entangled State

Based on A.K. Patis original idea [Phys. Rev. A 61 (2000) 022308] on single-qubit-state-assisted clone, very recently Zhan has proposed two assisted quantum cloning protocols of a special class of unknown two-qubit entangled states [Phys. Lett. A 336 (2005) 317]. In this paper we further generalize Zhans protocols such that an arbitrary unknown two-qubit entangled state can be treated.

Multiparty Quantum Secret Sharing of Classical Message using Cavity Quantum Electrodynamic System

An experimental feasible scheme of multiparty secret sharing of classical messages is proposed, based on a cavity quantum electrodynamic system. The secret messages are imposed at atomic Bell states initially in the senders possession by local unitary operations. By swapping quantum entanglement of atomic Bell states, the secret messages are split into several parts and each part is distributed to a separate party. In this case, any subset of the entire party group can not read out the secret message but the entirety via mutual cooperations. In this scheme, to discriminate atomic Bell states. This scheme is insensitive to the cavity decay and the thermal field, and usual joint Bell-state measurements are unnecessary.

Weakly Coupled Three-Layer Quantum Dot with a Charged Impurity inMagnetic Field*

The states of a weakly coupled 3-quantum-dot system with an external charged impurity located on the z-axis are studied in a magnetic field. The evolutions of the true ground state with the magnetic field B are obtained for various impurity cases. It is found that the negative charge impurity would promote the phase transition of the true ground state.

Sign flip in Giorgi-Pasquale-Paganelli model

Taking advantage of our improved gates as well as the Giorgi-Pasquale-Paganelli (GPP) nondestructive gate [Phys. Rev. A 70 (2004) 022319], the sign of any term of the initial state in the GPP model can be flipped. The success possibility of the sign Hip of odd number of terms is probabilistic (1/4), while the success possibility of the sign flip of even number of terms is deterministic (1).

Sodium atom in strong magnetic fields: a pseudospectral approach

Energies and wavefunctions of low-lying states and Rydberg states for the sodium atom in uniform magnetic fields varying from 0 to 105T are calculated using a pseudospectral approach with a model potential in spherical coordinates. The energies are comparable with experimental results as well as those obtained by other calculations. The spectra of oscillator strength are worked out. The evolution of them with the magnetic field is shown.

An Approach of the Nuclear Transition Charge Density Calculation in the Microscopic sdIBM-2

An approach to calculate the nuclear transition charge density (TCD) within the framework of the microscopic sdIBM-2 is presented and applied to the first. It was found that the TCD as well as the spectrum and some reduced transition matrix elements in can be reproduced quite satisfactorily on the same microscopic footing.