Ji-Bing Liu

N-qubitW state of spatially separated single molecule magnets.

A simple scheme is proposed to generate a N-qubit W state of spatiall separated single molecule magnets (SMM) in a cavity-fiber-cavity system. In the present scheme, the framework consisting of entangled qubits can be expediently designed according to our needs. By quantitatively discussing the case of N=4, we show that the effects of SMMs spontaneous decay and photon leakage out of fiber can be suppressed in our scheme due to the presence of virtual excited processes in SMM and fiber modes. Moreover, we also show that the present scheme is robust with respect to some deviations of experimental parameters, and as a result, the present investigation provides a research clue for realizing multi-partite entanglement between distant SMMs solid-state nanostructures, which may result in a substantial impact on the progress of multi-node quantum information network.

Continuous-variable entanglement in a two-mode four-level single-atom laser

This paper investigate the generation and evolution of continuous-variable entanglement in a two-mode single-atom laser, where the atomic coherence is induced by two classical laser fields (pump and coupling field) driving the corresponding atom transitions. It is found that the intensity of the coupling field can influence effectively the entanglement period of the cavity field. More importantly, our numerical results also show that the intensity and period of entanglement between the two cavity modes as well as the total mean photon number of the cavity field can be increased synchronously by adjusting the corresponding frequency detuning.

Single molecular magnets as a source of continuous-variable entanglement

We study the generation and evolution of continuous-variable entanglement in a single-molecular-magnets (SMM) system, where the quantum coherence effect is induced by two classical electromagnetic fields (pump and control fields). Our numerical results show that the entanglement of cavity fields can be controlled efficiently by tuning the intensity and frequency detuning of control field, and the macroscopic entangled light with long entanglement time can be realized in this SMM system, over a wide range of initial states of the cavity field. This investigation can be used for achieving the macroscopic entangled light in a solid-state medium, which is much more practical than that in an atomic or molecular medium because of its flexible design.

Quantum correlation and phase transitions in a two-dimensional doubly decorated Ising-Heisenberg model

We investigate the pairwise quantum correlation, characterized by quantum entanglement (QE) and quantum discord (QD), of a two-dimensional Ising-Heisenberg model on a planar doubly decorated lattice. At zero temperature, the concurrence (a measurement of pairwise entanglement) and the QD are related to the correlation function qxx and the staggered magnetization δSz, respectively, and both of them indicate the quantum phase transition (QPT) of the system. However, in a finite-temperature phase transition, all the pairwise entanglement vanishes thus it fails to detect the critical temperature TC, while the derivative of QD diverges at TC. This shows clearly that QD can capture the signal of phase transition in a separable state, thus it has a broader scope of application than QE in detecting phase transitions.

Slow vector optical solitons in a cold five-level hyper V-type atomic system

A new scheme of five-level hyper V-type atomic system is proposed with the aim of generating slow temporal vector optical solitons. Two transitions in the five-level atomic medium independently interact with the two orthogonally polarized components of a low intensity linear-polarized pulsed probe field, while two other transitions are driven by control laser fields. We demonstrate that various distortion-free slow temporal vector optical solitons, such as bright-bright, bright-dark, dark-bright and dark-dark vector solitons, can be evolved from the probe field. Besides, we also show that the modified Hubbard model that includes the Manakov system may be realized by adjusting the corresponding self- (cross-) phase modulation and dispersion effects of this system.

Ultraslow temporal vector optical solitons in a cold five-state atomic medium under Raman excitation

We theoretically investigate the formation of ultraslow temporal vector optical solitons in a lifetime-broadened five-state atomic system under Raman excitation. By analysing the interaction between the atomic system and two strong, linear-polarized continuous wave control fields and a weak, linear-polarized pulsed signal field, having two orthogonally polarized components, we find that the Maxwell equations of describing the propagation of two orthogonal polarization components can evolve into two coupled nonlinear Schrodinger equations, which admit solutions describing vector solitons, including bright–bright, bright–dark, dark–bright and dark–dark vector solitons with ultraslow group velocity. More importantly, the Manakov temporal vector solitons can be easily realized in our system by adjusting the corresponding parameters such as the Rabi frequencies of the control fields, one- and two-photon detunings. The unique features of the two coupled nonlinear Schrodinger equations are also discussed.

Efficient spin-filter and negative differential resistance behaviors in FeN4 embedded graphene nanoribbon device

In this paper, we propose a new device of spintronics by embedding two FeN4 molecules into armchair graphene nanoribbon and sandwiching them between N-doped graphene nanoribbon electrodes. Our first-principle quantum transport calculations show that the device is a perfect spin filter with high spin-polarizations both in parallel configuration (PC) and antiparallel configuration (APC). Moreover, negative differential resistance phenomena are obtained for the spin-down current in PC, and the spin-up and spin-down currents in APC. These transport properties are explained by the bias-dependent evolution of molecular orbitals and the transmission spectra.

Two-qubit Grover search in a dephasing-free subspace in cavity QED

Based on a cavity-assisted interaction by single-photon pulses, we propose a scheme to implement a two-qubit Grover search in a distributed quantum network, with qubits encoded in pairs of atoms in a dephasing-free subspace (DFS), which could strongly suppress collective dephasing errors and would be helpful for enhancing the fidelity of implementation. Moreover, we show that the preparation of entangled states and transfer of quantum states can be completed in our improved scheme, which is very important for the compatibility and scalability of the quantum network.

Generation of frequency entangled states via four-wave mixing in semiconductor well waveguide

We propose and analyze a scheme to realize a maximally frequency entangled state via four-wave mixing in semiconductor well waveguide. This scheme uses light hole transition to induce nonradiative quantum coherence in the waveguide. The results show that the transformation efficiency is perfect and the velocity of the entangled state is slow. By adjusting the intensity of strong controlling fields, the storing and retrieving process of the maximum entangled state can be achieved in our scheme.

Efficient spin-filtering, magnetoresistance and negative differential resistance effects of a one-dimensional single-molecule magnet Mn(dmit)2-based device with graphene nanoribbon electrodes

We present first-principle spin-dependent quantum transport calculations in a molecular device constructed by one single-molecule magnet Mn(dmit)2 and two graphene nanoribbon electrodes. Our results show that the device could generate perfect spin-filtering performance in a certain bias range both in the parallel configuration (PC) and the antiparallel configuration (APC). At the same time, a magnetoresistance effect, up to a high value of 103%, can be realized. Moreover, visible negative differential resistance phenomenon is obtained for the spin-up current of the PC. These results suggest that our one-dimensional molecular device is a promising candidate for multi-functional spintronics devices.