Zeng Hao-Sheng

Quantum thermal discord in a two-spin-1/2 XXZ model

We study the quantum discord in a two-spin-1/2 XXZ model in thermal equilibrium at temperature T in the presence of an external magnetic field B. Special attention is paid to the dependence of quantum discord on the temperature T and magnetic field B. It is found that quantum thermal discord is more robust than concurrence against temperature, in the sense that quantum thermal discord does not vanish at finite temperatures, but concurrence vanishes completely at a critical temperature.

Teleportation of Multi-qudit Entangled States

We propose a method to realize the teleportation of an unknown entangled state that consists of many qudits through a partially entangled-qudit quantum channel with the help of 2log2d-bit classical communication. The operations used in the teleportation process include a generalized Bell-state measurement and a series of single-qudit π-measurements performed by Alice, a series of generalized qudit-Pauli gates and two-level unitary gates, as well as a qubit measurement performed by Bob. For a maximally entangled quantum channel, the successful probability of the teleportation becomes unit.

Entanglement and non-Markovianity of a spin-S system in a dephasing environment

We study the entanglement (measured by negativity) evolution and the non-Markovianity for the dynamical process of a spin-S system embedded in dephasing environments. The exact analytical solution is presented, which shows that the decoherence function governs the evolutions of coherence, entanglement, and the non-Markovianity of the corresponding dynamical processes. For Ohmic and sub-Ohmic reservoirs, the negativity decreases monotonically in time and the corresponding dynamics is Markovian. While for super-Ohmic reservoirs with non-monotonic decoherence function, the negativity appears as the phenomenon of revival and the corresponding dynamics is non-Markovian. The relation between non-Markovianity and the system dimension is studied.

Controlled teleportation of multi-qudit quantum information

We propose a scheme for realizing a controlled teleportation of random M-qudit quantum information under the control of N agents. The resource consumption includes a prearranged (2M + N + 1)-qudit entangled quantum channel and (2M + N + 1) log2 d-bit classical communication. And the quantum operations used in the teleportation process are a series of generalized Bell-state measurements, single-qudit measurements, qudit H-gates, qudit-Pauli gates and qudit phase gates. It is shown that the original state can be restored by the receiver only on condition that all the agents work in collaboration with each others. If one agent does not cooperate with the other, the original state cannot be fully recovered.

Rotation of Bloch sphere induced by Lamb shift in open two-level systems

From a quite general form of the Lindblad-like master equation of open two-level systems (qubits), we study the effect of Lamb shift on the non-Markovian dynamics. We find that the Lamb shift can induce a non-uniform rotation of the Bloch sphere, but that it does not affect the non-Markovianity of the open system dynamics. We determine the optimal initial-state pairs that maximize the backflow of information for the considered master equation and find an interesting phenomenon–the sudden change of the non-Markovianity. We relate the dynamics to the evolution of the Bloch sphere to help us comprehend the obtained results.

Efficient State Preparation via Ion Trap Quantum Computing and Quantum Searching Algorithm

We present a scheme to prepare a quantum state in a ion trap with probability approaching to one by means of ion trap quantum computing and Grovers quantum search algorithm acting on trapped ions.We present a scheme to-prepare a quantum state in an ion trap with probability approaching to one by means of ion trap quantum computing and Grovers quantum search algorithm acting on trapped ions.

Preparation of GHZ States via Grover's Quantum Searching Algorithm

In this paper we propose an approach to prepare GHZ states of an arbitrary multi-particle system in terms of Grovers fast quantum searching algorithm. This approach can be regarded as an extension of the Grovers algorithm to find one or more items in an unsorted database.We propose an approach to prepare GHZ (Greenberger, Horne, Zeilinger) states of an arbitrary multi-particle system in terms of Grovers fast quantum searching algorithm. The approach can be used to produce other entangled states with various degrees of entanglement.

Controlled Telecloning and Teleflipping for One-Qubit Pure States

We propose a scheme for realizing controlled 1 → 2 telecloning and 1 → 1 teleflipping for one-qubit pure states via a quantum network including N agents. The quantum operations used in the information-transmission process are just only one Bell-state measurement, and a series of single-qubit operation. It is shown that the fidelities of the controlled telecloning and teleflipping are independent of the initial states and reach their optimal values of 5/6 and 2/3 respectively on the condition that all the agents collaborate. If any one agent does not cooperate, the fidelities become state-dependent and are always smaller than the corresponding optimal values. The average fidelities are equal to the balanced value 1/2, which implies that on average the state incepted by any one of the receivers is a fully mixed state. Thus no information leaks out to any dishonest receivers. The security of telecloning and teleflipping have been increased greatly.

Discontinuity and Protection of Quantum Fisher Information for a Two-Qubit System

We analytically investigate the dynamics of quantum Fisher information of two qubits in independent environments for both uncorrelated and entangled input states. Especially, we observe that, in the non-Markovian regime and resonant case, quantum Fisher information of uncorrelated input state vanishes only at discrete time point whereas that of entangled input state can disappear during finite time interval. It shows that quantum Fisher information, which determines the parameter estimation precision, is strongly affected by the environment memory effects, and the advantage of entanglement-enhance metrology no longer exists even for a very short time. We also note that quantum Fisher information for two kinds of input states can be preserved under appropriate qubit-reservoir detuning.

Distributed quantum information processing via quantum dot spins

We propose a scheme to engineer a non-local two-qubit phase gate between two remote quantum-dot spins. Along with one-qubit local operations, one can in principal perform various types of distributed quantum information processing. The scheme employs a photon with linearly polarisation interacting one after the other with two remote quantum-dot spins in cavities. Due to the optical spin selection rule, the photon obtains a Faraday rotation after the interaction process. By measuring the polarisation of the final output photon, a non-local two-qubit phase gate between the two remote quantum-dot spins is constituted. Our scheme may has very important applications in the distributed quantum information processing.