Bidirectional Controlled Quantum Teleportation via Two Pairs of Bell States

International Journal of Theoretical Physics - We propose a bidirectional controlled teleportation scheme using two pairs of Bell states as quantum channels. This solution uses Charlie as the...     

High Fidelity Symmetric Telecloning and Entanglement Distribution of Spin Quantum States by Weak Measurement and Reversal

We propose a physical realization of robust symmetric telecloning scheme for spin quantum states by employing the weak measurement and reversal (WMR) operation. Using proper WMR, the ultrahigh telecloning fidelity and long distance of quantum state transfer with certain success probability can be achieved. More interestingly, the lowest average telecloning fidelity can attain 80 %, which is almost independent of the spin chain length. We also study the properties of entanglement distribution via the spin chain for arbitrary two-qubit entangled pure states as inputs and find that the WMR operation indeed helps for protecting distributed entanglement.     

Quantum Teleportation via Hybrid Entangled States

In this paper, we study quantum teleportation of atomic states via a hybrid entangled state (HES) involving an atom and a cavity field. And we investigate how to implement controlled phase (CP) gates between atomic internal Finally, a brief discussion about the feasibility of this scheme in experiment is presented.     

A Direct Measurement Scheme of Two Quantum-Dot Qubits Quantum Correlation via Detector Current

By using the rate equation method we have investigated a scheme for measuring the quantum discord between two double quantum dot qubits via the current in quantum point-contact devices. The current of the detectors is same in-phase as the time-dependant of the quantum discord, and we can read out the most important time point when the quantum discord or quantum correlation reaches its maximum or minimum. Furthermore, in a special initial condition, the current can reflect the quantum discord. The shot noise of the detectors is calculated numerically. Which is dominated by the measured signal in single shot experiments.     

Quantum State Transfer via Parity Measurement

We propose two schemes for quantum state transfer using parity measurement in a cavity-waveguide system, and the two schemes can be generalized to multidipole’s case. An important advantage is that quantum state transfer can be completed by single-qubit rotations and the measurement of parity. Therefore, our scheme can be realized in the scope of current experimental technology.     

Evolution of Quantum States Simultaneously Undergoing Two Kinds of Quantum Noises

International Journal of Theoretical Physics - Using the thermal-entangled state representations, we obtain the analytical evolution of quantum states simultaneously undergoing two kinds of quantum...     

Ground States of Quantum Antiferromagnets in Two Dimensions

We explore the ground states and quantum phase transitions of two-dimensional, spin S=1/2, antiferromagnets by generalizing lattice models and duality transforms introduced by Sachdev and Jalabert (1990, Mod. Phys. Lett. B4, 1043). The minimal model for square lattice antiferromagnets is a lattice discretization of the quantum nonlinear sigma model, along with Berry phases which impose quantization of spin. With full SU(2) spin rotation invariance, we find a magnetically ordered ground state with Néel order at weak coupling and a confining paramagnetic ground state with bond charge (e.g., spin Peierls) order at strong coupling. We study the mechanisms by which these two states are connected in intermediate coupling. We extend the minimal model to study different routes to fractionalization and deconfinement in the ground state, and also generalize it to cases with a uniaxial anisotropy (the spin symmetry groups is then U(1)). For the latter systems, fractionalization can appear by the pairing of vortices in the staggered spin order in the easy-plane; however, we argue that this route does not survive the restoration of SU(2) spin symmetry. For SU(2) invariant systems we study a separate route to fractionalization associated with the Higgs phase of a complex boson measuring noncollinear, spiral spin correlations: we present phase diagrams displaying competition between magnetic order, bond charge order, and fractionalization, and discuss the nature of the quantum transitions between the various states. A strong check on our methods is provided by their application to S=1/2 frustrated antiferromagnets in one dimension: here, our results are in complete accord with those obtained by bosonization and by the solution of integrable models.     

Quantum Tasks with Non-maximally Quantum Channels via Positive Operator-Valued Measurement

By using a proper positive operator-valued measure (POVM), we present two new schemes for probabilistic transmission with non-maximally four-particle cluster states. In the first scheme, we demonstrate that two non-maximally four-particle cluster states can be used to realize probabilistically sharing an unknown three-particle GHZ-type state within either distant agent’s place. In the second protocol, we demonstrate that a non-maximally four-particle cluster state can be used to teleport an arbitrary unknown multi-particle state in a probabilistic manner with appropriate unitary operations and POVM. Moreover the total success probability of these two schemes are also worked out.     

Decoherence Suppression in Phase Decoherence Environment Using Weak Measurement and Quantum Measurement Reversal

Decoherence suppression from disturbance of the environment is an essential task in quantum information processing. We investigate decoherence suppression of a qubit system interacting with a heat bath with phase decoherence by employing the weak measurement (WM) and quantum measurement reversal (QMR) operation. We show explicitly that the qubit decoherence can be efficiently completely suppressed by means of the combination WM and QMR, which is independent of the form of the spectral density of the reservoir and the form of initial input state.     

Deterministic Quantum Controlled Teleportation of Arbitrary Multi-qubit States via Partially Entangled States

In this paper, an efficient proposal for quantum controlled teleporatation of arbitrary multi-qubit states is presented via three-qubit non-maximally entangled states. The successful probability is viewed as one of the most important performance parameters for quantum teleportation. The significant advantage of our scheme is that the successful probability is independent of the coefficients of partially entangled states, and is always equal to 100% in spite of using non-maximally quantum channel. From the concrete implementation processes of this proposal, it could be found that only the usual Bell-state measurement, simple single-qubit projective measurement and common single-qubit local unitary operations, of which the physical realization has been widely explored, need to be performed without the introduction of auxiliary particles.     

两个腔模相关量子态的制备

提出一种制备两个腔模的相关量子态的方法。在本方法中,一系列的级联型三能级原子逐个地穿过两个初始时处于真空态的单模腔,然后,对这些原子进行控测。在一定条件下,两个腔模被制备到相关量子态。     

Geometry of Quantum Coherence for Two Qubit X States

The geometry of the structure of entanglement and discord for Bell-diagonal states is depicted by Lang and Caves (Phys. Rev. Lett. 105, 150501, 2010). In this paper, we investigate the geometry with respect to several distance-based quantifiers of coherence for Bell-diagonal states. We find that as both l₁ norm and relative entropy of coherence vary continuously from zero to one, their related geometric surfaces move from the region of separable states to the region of entangled states, a fact illustrating intuitively that quantum states with nonzero coherence can be used for entanglement creation. We find the necessary and sufficient conditions that quantum discord of Bell-diagonal states equals to its relative entropy of coherence, and depict the surfaces related to the equality. We give surfaces of relative entropy of coherence for X states. We show the surfaces of dynamics of relative entropy of coherence for Bell-diagonal states under local nondissipative channels and find that all coherences under local nondissipative channels decrease.

     

A Secure Quantum Communication via Deformed Tripartite Coherent States

We propose a secure quantum-network protocol using Greenberger–Horne–Zeilinger (GHZ) tripartite deformed states. Alice and Bob share a secure key by exchanging the entangled deformed states without basis reconciliation. We investigate a perfect transmission efficiency in a perfect quantum channel. The security of the protocol is ensured by the deformed and correlated tripartite states, which allows us to detect any eavesdropping easily.     

Efficient Verifiable Quantum Secret Sharing Schemes via Eight-Quantum-Entangled States

International Journal of Theoretical Physics - Quantum secret sharing (QSS) protocols are designed to allow a secret message to be divided into several shadows, and the secret can be reconstructed...     

Generation of Quantum States for Atomic Ensemble via Cavity QED

A scheme is proposed for generating quantum states of atomic ensemble. In this scheme, a beam of three-level atoms in the Λ configuration is trapped in a cavity, then squeezed vacuum state and squeezed coherent state of the atomic ensemble are prepared by choosing different initial states of the system. The scheme is based on the off-resonant interaction between the atom and cavities, so the high-level of the atom is eliminated adiabatically.     

Protecting Entanglement in a Common Phase Decoherence Environment using Weak Measurement and Quantum Measurement Reversal

Protection of entanglement from disturbance of the environment is an essential task in quantum information processing. We investigate the entanglement protection of a qubit-qubit system interacting with a phase decoherence reservoir by employing the weak measurement (WM) and quantum measurement reversal (QMR). We show explicitly that the quantum entanglement can be obviously protected by means of the proper WM and QMR. In particular, we found that there is a specific initial state parameter region, the entanglement protection ratio, which is determined only by the initial state parameter and independent of the form of the spectral density of the reservoir.