摘要：
For carrying out many quantum information protocols entanglement must be established in advance between two distant parties. Practically, inevitable interaction of entangled subsystems with their environments during distribution and storage will result in degradation of entanglement. Here we show that some partially entangled states are more robust than maximally entangled states in terms of the residual quantum correlation measured by concurrence, fully entangled fraction, and quantum discord, respectively. This phenomenon leads to the fact that nonmaximally entangled states can outperform maximally entangled states for quantum correlation distribution and storage under the amplitude damping. These results can also educe a noticeable consequence that the ordering of states under quantum correlation monotones can be reversed even by local trace-preserving and completely positive maps.
摘要：
We investigate collective radiant properties of two separated atoms in X-type quantum states. We show that quantum correlations measured by quantum discord (QD) can trigger and enhance superradiance and subradiance in the two-atom system even though in the absence of interatomic quantum entanglement. We also explore quantum statistical properties of photons in the superradiance and subradiance by addressing the second-order correlation function. In particular, when the initial state of the two separated atoms is the Werner state with nonzero QD, we find that radiation photons in the superradiant region exhibit the nonclassical sub-Poissonian statistics and the degree of the sub-Poissonian statistics increases with increasing of the QD amount, while radiation photons in the subradiant region have either the sub-Poissonian or super-Poissonian statistics depending on the amount of QD and the directional angle. In the subradiant regime, we predict the QD-triggered photon statistics transition from the super-Poissonian to sub-Poissonian statistics. These results shed a new light on applications of QD as a quantum resource.
摘要：
The purpose of this paper is to investigate the effects of quantum noises on entanglement localization by taking an example of reducing a three-qubit Greenberger-Horne-Zeilinger (GHZ) state to a two-qubit entangled state. We consider, respectively, two types of quantum decoherence, i.e. amplitude-damping and depolarizing decoherence, and explore the best von Neumann measurements on one of three qubits of the triple GHZ state for making the amount of entanglement of the collapsed bipartite state be as large as possible. The results indicate that different noises have different impacts on entanglement localization, and that the optimal strategy for reducing a three-qubit GHZ state to a two-qubit one via local measurements and classical communications in the amplitude-damping case is different from that in the noise-free case. We also show that the idea of entanglement localization could be utilized to improve the quality of bipartite entanglement distributing through amplitude-damping channels. These findings might shed a new light on entanglement manipulations and transformations.
摘要：
We propose new methods to construct universal Greenberger-Horne-Zeilinger (GHZ)-state analyzers without destroying the qubits by using two-qubit parity gates. The idea can be applied to any physical systems where the two-qubit parity gate can be realized. We also investigate the feasibility of nondestructively distinguishing the GHZ-basis states for photonic qubits with such an idea. The nondestructive GHZ-state analyzers can act as generators of GHZ entangled states and are expected to find useful applications for resource-saving quantum information processing.
通讯机构：
[Wang, Xin-Wen] H;Hengyang Normal Univ, Dept Phys & Elect Informat Sci, Hengyang 421002, Peoples R China.
关键词：
Remote information concentration;multipartite entanglement;qudit
摘要：
Telecloning and its reverse process, referred to as remote information concentration (RIC), have attracted considerable interest because of their potential applications in quantum-information processing. We here present a general scheme for RIC in d-level systems (qudits), in which the quantum information initially distributed in many spatially separated qudits can be remotely and deterministically concentrated to a single qudit via an entangled channel without performing any global operations. We show that the entangled channel of RIC can be different types of entangled states, including mixed states as well as pure ones. More interestingly, these mixed states include a bound entangled state which has a similar form to the generalized Smolin state but has different characteristics from it. We also show that there exists a multipartite entangled state which can be used to implement both telecloning and RIC in the two-level system. Our many-to-one RIC protocol could be slightly modified to perform some types of many-to-many RIC tasks.
摘要：
It has been shown that two-photon parity check has widespread applications in optical quantum information processing. In recent years much effort has been made to implement nondestructive two-photon parity detection using cross-Kerr nonlinearity (XKNL) effect. We here put forward an XKNL-based scheme for nearly deterministic two-photon parity detection without destroying the photons, in which the required cross-Kerr phase shift could be much (even several orders of magnitude) smaller than that required for previous schemes. The scheme utilizes a ring cavity fed by a coherent state beam as a quantum information bus which interacts with one of the two path modes of two polarized photons through a cross-Kerr medium. The measurement outcome of the bus mode reveals the polarization-parity of the two photons.
摘要：
We propose a method to construct a nondestructive n-qubit Greenberger– Horne–Zeilinger (GHZ)-state analyzer. The method is applied to any systems in which two-qubit parity gates, controlled-phase gates, or controlled-NOT gates can be realized. We also present a simplified two-photon parity gate with which a nondestructive n-photon GHZ-state analyzer could be largely simplified. The nondestructive GHZ-state analyzer is expected to find useful applications for economical quantum-information processing.
摘要：
A scheme is presented for generating four-photon Greenberger-Hornc-Zeilinger(GHZ) states with resonant interaction between a cascade type three-level atom and two bimodal cavities.In the proposed protocol,the quantuni information is encoded on Fock states of the cavity fields.Schrodinger equation of the system is solved and quantum states of interaction system are obtained.The detection of atom can collapse cavity to the desired GHZ state.It is shown that the scheme is simple and the experimental implementation is feasible.
通讯机构：
[Wang, Xin-Wen] H;Hengyang Normal Univ, Dept Phys & Elect Informat Sci, Hengyang 421008, Peoples R China.
摘要：
The cross-Kerr nonlinearity (XKNL) effect can induce efficient photon interactions in principle with which photonic multiqubit gates can be performed using far fewer physical resources than linear optical schemes. Unfortunately, it is extremely challenging to generate giant cross-Kerr nonlinearities. In recent years much effort has been made to perform multiqubit gates via weak XKNLs. However, the required nonlinearity strengths are still difficult to achieve in an experiment. We here propose an XKNL-based scheme for realizing a two-photon polarization-parity gate, a universal two-qubit gate, in which the required strength of the nonlinearity could be orders of magnitude weaker than those required for previous schemes. The scheme utilizes a ring cavity fed by a coherent state as a quantum information bus which interacts with a path mode of the two polarized photons (qubits). The XKNL effect makes the bus pick up a phase shift dependent on the photon number of the path mode. Even when the potential phase shifts are very small they can be effectively measured using photon-number resolving detectors, which accounts for the fact that our scheme can work in the regime of tiny XKNL. The measurement outcome reveals the parity (even parity or odd parity) of the two polarization qubits.
摘要：
A In this paper, according to the a-monomer and β-monorner in the cytoskeletal microtubules and Lloyd＇s schemes for loading and processing of information in the wall of microtubules, quantum information process in the cerebral nervous system is discussed. We conclude that there is a quantum information process in the tubulin. Fur- ther, the quantum information process in cytoskeletal mierotuboles is described based on the pseudo-spin atoms model, and system＇s Hamiltonian is discussed.
摘要：
A simple scheme is presented for generating 2n-mode photon Greenberger-Horne-Zeilinger (GHZ) states with the interaction of a 2n-level atom with two n-mode cavities.In the proposed protocol, the 2n qubits are encoded in zero-and one-photon Fock states of 2n cavity modes.Because the interaction between the atom and cavity fields is resonant,the coupling strength can be relative strong.This will shorten the corresponding interaction time and thus reduce the effect of decoherence in experiment.
作者机构：
[汪新文; 张登玉; 谢利军; 詹孝贵; 唐世清; 陈银花] Department of Physics and Electronic Information Science, Hengyang Normal University, Hengyang 421008, China
通讯机构：
[Deng-yu Zhang] D;Department of Physics and Electronic Information Science, Hengyang Normal University, Hengyang, China
关键词：
Entangle State;Cavity Mode;Quantum Information Processing;Cavity Field;Multipartite Entangle State
摘要：
A simple scheme is presented for generating four-photon Greenberger-Horne-Zeilinger （GHZ） states with interaction between a four-level atom and two bimodal cavities. In the proposed protocol, the quantum information is encoded on Fock states of the cavity fields. The detection of the atom can collapse the cavity to the desired state. The experimental feasibility of our proposal is also discussed.
摘要：
In practice, the initial state of ancillary systems (analogous to a bunch of papers in daily copier) in quantum cloning are usually set to vacuum state. However, this is an experimental challenge. Here, we focus on the 1→2 optimal universal cloning for qubits, and investigate the effect of a nonideal case that the ancillary system is initially prepared in a superposition state
$x|0\rangle+y|1\rangle$
instead of precise vacuum state, because of experimental imperfections. It is shown that the fidelities of two clones are then not the same and dependent of both the input state and the initial superposition state of the ancillary system. We analyze the mean fidelities of clones over all possible input states, and reveal that the average of two fidelities is a parabolic function of |y|. Our result may be helpful for analyzing the experimental infidelities of clones, and thus contribute to the experimental improvement.
