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991.
CAO Min LING Yin-Sheng ZHU Shi-Qun 《理论物理通讯》2009,51(5):811-814
We calculate the eigenvalues and eigenvectors of a five-qubit isotropic Heisenberg model in an external magnetic field, and give analytical results for the concurrence of two nearest-neighbor qubits. A magnetic field can eliminate degeneration and change the ground state of the system. Therefore increasing the value of the magnetic field can induce entanglement in a certain range both for the antiferromagnetic and ferromagnetic case. 相似文献
992.
Based on the fact that a two-mode squeezed number state is a
two-variable Hermite polynomial excitation of the two-mode squeezed
vacuum state, the result of one-mode l-photon measurement for the
two-mode squeezed number state $S_2|m,n\rangle$ is discussed. It is found that a remaining field-mode simultaneously
collapses into a number state $|n-m+l\rangle$ with
the coefficient being a Jacobi polynomial of n, m and l, which manifestly exhibits the entanglement
between the two modes, i.e. it depends on the number-difference
between the two modes. The second mode collapses into an excited
coherent state when the first mode is measured as a coherent state. 相似文献
993.
The security of quantum secret sharing based on entanglement
swapping is revisited and a participant attack is presented. In this
attack two dishonest agents together can illegally recover the
secret quantum state without the help of any other controller, and
it will not be detected by any other users. Furthermore, by
modifying the distribution process of particles and adding a
detection step after each distribution process, we propose an
improved protocol which can resist this kind of attack. 相似文献
994.
In this paper, we study the entanglement dynamics of atoms
locally coupled to a cavity field. By studying two different models
within the framework of cavity QED, we show that the so-called
atomic entanglement sudden death always occurs if initially the
cavity field is in the thermal state, in clear contrast with that in
the vacuum state where the same entanglement decay is in infinite
time. 相似文献
995.
Nonlocal decoherence of two qubits due to pure phase damping has been investigated. We have proposed a scheme to keep the entanglement of two qubits from nonlocal decoherence. By applying a series of ±π pulses, nonlocal decoherence can be thoroughly suppressed. 相似文献
996.
We propose a simple scheme to not only generate GHZ states and W states of the multiparticle but also form a new category of multiparticle entangled states by letting the λ-type three-level atoms simultaneously interacting with a coherent cavity field followed by the selective measurements on the cavity mode. We investigate the influence of the cavity dissipation on the generated entangled state and discuss the experimental feasibility of our scheme. It is shown that the intensity of the coherent cavity field plays an instructive role in contribution to state preparation process while the cavity decay and the detuning between the atoms and cavity mode result in the deterioration of the generated entangled state. 相似文献
997.
The effect of Dzialoshinski-Moriya (DM) interaction on thermal entanglement of a two-qubit XXZ spin chain in a homogenous magnetic field is investigated. It is found that the DM interaction can enhance thermal entanglement. When D is large enough, the entanglement can exist for larger temperatures and strong magnetic field. 相似文献
998.
XU Feng WANG An-Min ZHAO Ning-Bo SU Xiao-Qiang ZHU Ren-Gui 《理论物理通讯》2006,46(4):591-594
Energy is introduced as an entanglement witness to describe the entanglement property of a quantum system. The thermal equilibrium system is guaranteed to be entangled when system is cooled down below the entanglement temperature TE. By virtue of this concept we exploit the minimum separable state energy and entanglement temperature TE of the bilinear-biquadratic antiferromagnetic spin-1 chain model. We numerically calculate TE for arbitrary values of the strength of biquadratic exchange interaction Q up to N=7. We find TE decreases with Q for fixed N when Q is between -3 and 1/3 (J = 1). In this regime TE also decreases with N for fixed Q and varies slowly for large N. While the thermal system is always entangled when Q is smaller than -3. 相似文献
999.
XIE Guo-Qiu WANG An-Min MA Xiao-San 《理论物理通讯》2006,46(1):73-76
The entanglement evolution of multipartite quantum states under a spin environment is analyzed. Due to interaction, the extent to which the entanglement vanishes depends not only on the size of system and the structure of quantum states, but also on the exchange couplings with environment. The decoherence-free subspaces have been identified by using the linear entropy. 相似文献
1000.