Quantum Dense Coding in Multiparticle Entangled States via Local Measurements

We study quantum dense coding between two arbitrarily fixed particles in a (N 2)-particle maxlmally-entangled states through introducing an auxiliary qubit and carrying out local measurements. It is shown that the transmitted classical information amount through such an entangled quantum channel is usually less than two classical bits. However, the information amount may reach two classical bits of information, and the classical information capacity is independent of the number of the entangled particles under certain conditions. The results offer deeper insight into quantum dense coding via quantum channels of multi-particle entangled states.     

A Scheme for Dense Coding in the Non-Symmetric Quantum Channel

We investigate the dense coding in the case of non-symmetric Hilbert spaces of the sender and receiver‘s particles sharing the quantum maximally entangled state. The efficiency of gaining classical information is also considered.We conclude that when a more level particle is with the sender, she can obtain a non-symmetric quantum channel from a symmetric one by entanglement transfer. Thus the efficiency of information transmission is improved.     

New Quantum Private Comparison Protocol Using χ-Type State

We present a new quantum private comparison protocol based on the four-particle χ-type states. Different from previous protocols using the four-particle χ-type states, our protocol have some advantages. Without using the entangled character, we only need to prepare one type of χ-type state and N χ-type states. And we use the Pauli local unitary operation on particles to encode the information and to extract information by measurement. We also discuss that our protocol can withstand all various kinds of outside attacks and participant attacks.     

A Blind Quantum Signature Scheme with χ-type Entangled States

A blind quantum signature scheme with χ-type entangled states is proposed, which can be applied to E-voting system. In this scheme, the particles in χ-type state sequence are used for quantum key distribution first, and then for quantum signature. Our scheme is characterized by its blindness, impossibility of forgery, impossibility of disavowal. In addition, our scheme can perform an audit program with respect to the validity of the verification process in the light of actual requirements. The security of the scheme is also analyzed.     

Linear Optical Implementation for Quantum Teleportation of Unknown Two-Qubit Entangled States

We present a linear optical implementation for quantum teleportation of an unknown two-qubit entangled state by using linear optical elements, such as beam splitters, phase shifters, and half wave plates. This method is based on the single photon representation of quantum bits. Four location qubits and one polarization qubit are used to realize quantum logical operations in the teleportation procedure of the unknown two-qubit entangled state.     

Scheme for Cloning an Unknown Entangled State with Assistance via Non-maximally Entangled Cluster States

We propose a scheme for cloning unknown two-particle entangled state and its orthogonal complement state with assistance from a state preparer. Two stages were included in this scheme. The first stage requires usual teleportation by using a one-dimensional non-maximally four-particle cluster state as quantum channel, after Alice’s (the state sender) Bell measurement, Bob (the state receiver) can get the original state with certain probability. In the second stage, after having received Victor’s (the state preparer) classical message, the perfect copies and complement copies of an unknown state can be produced in Alice’s place, the probability of Alice to get the original state or its orthogonal complement state are calculated. Assisted cloning of an arbitrary unknown two-particle entangled state is discussed in the latter scheme.     

Constructing Entanglement Witnesses for States in?Infinite-Dimensional Bipartite Quantum Systems

In this paper, two approaches of constructing entanglement witnesses for finite- or infinite-dimensional bipartite quantum systems are presented. Let H _A and H _B be complex Hilbert spaces and {E _k } and {F _k } be sequences of self-adjoint Hilbert-Schmidt operators on H _A and H _B , respectively, such that Tr(E^f_kE_l)=Tr(F^f_kF_l)=d_kl\mathrm{Tr}(E^{\dag}_{k}E_{l})=\mathrm{Tr}(F^{\dag}_{k}F_{l})=\delta_{kl}. Then W=I−∑ _k E _k ⊗F _k is an entanglement witness on H _A ⊗H _B if W\not 3 0W\not\geq 0. If ρ is an entangled state and τ ₀ is the nearest separable state to ρ under the Hilbert-Schmidt norm, then W=c ₀ I+τ ₀−ρ with c ₀=Tr[τ ₀(ρ−τ ₀)] is an entanglement witness.     

fficient Scheme for Implementing a Fredkin Gate via Resonant Interaction with Two-Mode Cavity Quantum Electrodynamics

A scheme for implementing a Fredkin gate with an atom sent through a microwave cavity is proposed. The scheme is based on the resonant atom-cavity interaction so that the gating time is sharply short, which is important in view of decoherence.     

Decoy States and Low-Density Parity-Check Error-Correcting Codes in Quantum Cryptography with Phase–Time Coding

Journal of Experimental and Theoretical Physics - The cryptographic robustness of quantum key distribution (QKD) with phase–time coding against a photon number splitting (PNS) attack is...     

An Efficient Scheme for Implementing an N-Qubit Toffoli Gate with Superconducting Quantum-Interference Devices in Cavity QED

An alternative approach is proposed to realize an n-qubit Toffoli gate with superconducting quantum-interference devices （SQUIDs） in cavity quantum electrodynamics （QED）. In the proposal, we represent two logical gates of a qubit with the two lowest levels of a SQUID while a higher-energy intermediate level of each SQUID is utilized for the gate manipulation. During the operating process, because the cavity field is always in vacuum state, the requirement on the cavity is greatly loosened and there is no transfer of quantum information between the cavity and SQUIDs.     

Wentzel—Kramers—Brillouin Approximation for Dynamic Systems with Kinetic Coupling in Entangled State Representations

We study the Wentzel-Kramers-Brillouin (WKB) approximation for dynamic systems with kinetic couplings in entangled state representations.The result shows that the kinetic coupling will affect the position of classical turning points where the condition of using the WKB approximation breaks down.The modified WKB approximation formula is derived in the entangled state representation,for example,the common eigenvector of the relative coordinate and the total momentum of two particles.The corresponding Bohr-Sommerfeld quantization rule is also derived.     

Simulation study of χc→J/Ψ+γ detection with J/Ψ→e+e? in pp collisions in the ALICE experiment at LHC

We present Monte Carlo preliminary results about the feasibility to detect the χ _c family in p-p collisions at 14 TeV in the ALICE Central Barrel at CERN LHC. The χ _c1 and χ _c2 were forced to decay in the radiative channel J/Ψ+γ→e ⁺ e ⁻+γ and were merged with a proton-proton non-biased collision. After Monte Carlo transport and simulation of the detector response, the e ⁺, e ⁻ and converted γ were reconstructed and identified in the ALICE ITS, TPC and TRD detectors. Separate signals corresponding to γ from χ _c1 and from χ _c2 were observed. The position and relative weight of the fit to gaussians agreed with the input values within the statistical limits. An erratum to this article can be found at     

Quantum coherence in λ-three-level system driven by bichromatic coupling field

We present a theoretical study of quantum coherent effects in a λ-three-level system with a strong bichromatic coupling field and a weak probe field. When one component of the strong bichromatic coupling field is resonant with a corresponding transition and the other is detuning with an integer fraction of the Rabi frequency of the resonant field, the absorption spectrum exhibits a series of symmetrical doublets. While two frequencies of the strong bichromatic coupling field are symmetrically detuned from the transition, the position and the relative intensity of the absorption peak are both affected by the coupling field intensity and detuning. An explanation of the spectrum is given in term of the dressed-state formalism.     

Quantum steganography with large payload based on entanglement swapping of χ-type entangled states

In this paper, we firstly propose a new simple method to calculate entanglement swapping of χ-type entangled states, and then present a novel quantum steganography protocol with large payload. The new protocol adopts entanglement swapping to build up the hidden channel within quantum secure direct communication with χ-type entangled states for securely transmitting secret messages. Comparing with the previous quantum steganographies, the capacity of the hidden channel is much higher, which is increased to eight bits. Meanwhile, due to the quantum uncertainty theorem and the no-cloning theorem its imperceptibility is proved to be great in the analysis, and its security is also analyzed in detail, which is proved that intercept-resend attack, measurement-resend attack, ancilla attack, man-in-the-middle attack or even Dos(Denial of Service) attack couldn't threaten it. As a result, the protocol can be applied in various fields of quantum communication.     

A simple scheme to generate χ-type four-charge entangled states in circuit QED

We propose a simple scheme to generate χ-type four-charge entangled states by using SQUID-based charge qubits capacitively coupled to a transmission line resonator (TLR). The coupling between the superconducting qubit and the TLR can be effectively controlled by properly adjusting the control parameters of the charge qubit. The experimental feasibility of our scheme is also shown.     

Rogue Wave Solutions for Nonlinear Schrdinger Equation with Variable Coefficients in Nonlinear Optical Systems

In this paper, the generalized Darboux transformation is constructed to variable coefficient nonlinear Schrdinger(NLS) equation. The N-th order rogue wave solution of this variable coefficient NLS equation is obtained by determinant expression form. In particular, we present rogue waves from first to third-order through some figures and analyze their dynamics.     

Resonance contributions from χc0 in charmless three-body hadronic B meson decays

Within the framework of perturbative QCD factorization, we investigate the nonfactorizable contributions to the factorization-forbidden quasi-two-body decays \begin{document}$ B_{(s)}\rightarrow h\chi_{c0}\rightarrow h\pi^+\pi^-(K^+K^-) $\end{document} with \begin{document}$ h=\pi, K $\end{document}. We compare our predicted branching ratios for the \begin{document}$ B_{(s)}\rightarrow K\chi_{c0}\rightarrow K\pi^+\pi^-(K^+K^-) $\end{document} decay with available experiment data as well as predictions by other theoretical studies. The branching ratios of these decays are consistent with data and other theoretical predictions. However, in the Cabibbo-suppressed decays \begin{document}$ B_{(s)}\rightarrow h\chi_{c0}\rightarrow h\pi^+\pi^-(K^+K^-) $\end{document} with \begin{document}$ h=\bar{K}^0,\pi $\end{document}, the values of the branching ratios are of the order of \begin{document}$ 10^{-7} $\end{document} and \begin{document}$ 10^{-8} $\end{document}. The ratio \begin{document}$ R_{\chi_{c0}} $\end{document} between the decays \begin{document}$B^+\rightarrow $\end{document}\begin{document}$ \pi^+\chi_{c0}\rightarrow \pi^+\pi^+\pi^-$\end{document} and \begin{document}$ B^+\rightarrow K^+\chi_{c0}\rightarrow K^+\pi^+\pi^- $\end{document} and the distribution of branching ratios for different decay modes in invariant mass are considered in this study.     

A Theoretical Scheme for Multi—user Quantum Key Distribution with N Einstein—Podolsky—Rosen Pairs on a Passive Optical Network

We propose a theoretical scheme for any-to-any multi-user quantum key distribution on a passive optical network with ordered N Einstein-Podolsky-Rosen Pairs.This scheme is safe and more efficient than those with single photons.Its efficiency approaches 100% in the limit that the number of pairs used in the eavesdropping check becomes negligible.It also has high capacity and is convenient for users.     

Cross sections for 68Ge production in natural- and enriched-germanium targets irradiated with protons of energy 100 MeV and background in experiments devoted to searches for the 2β0ν decay of 76Ge

The rate of ⁶⁸Ge production at sea level under the effect of the nuclear component of cosmic rays is calculated. The calculation is based on the experimental values of the cross sections for ⁶⁸Ge production in natural- and enriched-germanium targets (enrichment in ⁷⁶Ge) irradiated with high-energy protons. The background from the decays of ⁶⁸Ge can be a serious problem in new-generation experiments devoted to searches for the 2β0ν decay of ⁷⁶Ge.