Liu Xiao-Juan

Fabrication and temperature-dependent photoluminescence spectra of Zn—Cu—In—S quaternary nanocrystals

A series of Zn—Cu—In—S nanocrystals (ZCIS NCs) are prepared and the optical properties of the ZCIS NCs are tuned by adjusting the reaction time. It is interesting to observe that the temperature-dependent photoluminescence (PL) spectra of the ZCIS NCs show a redshift with decreasing intensity at low temperature (50–280 K) and a blueshift at high temperature (318–403 K). The blueshift can be explained by the thermally active phonon-assisted tunneling from the excited states of the low-energy emission band to the excited states of the high-energy emission band.

Chaos Synchronization in Two Coupled Duffing Oscillators

We have obtained two general unstable periodic solutions near the homoclinic orbits of two coupled Duffing oscillators with weak periodic perturbations by using the direct perturbation technique. Theoretical analysis reveals that the stable periodic orbits are embedded in the Melnikov chaotic attractors. The corresponding numerical results show that the phase portraits in the (x,u) and (y,v) planes are identical and are synchronized when the parameters of the two coupled oscillators are identical, but they are different and asynchronized when there is any difference between these parameters. It has been shown that the system parameters play a very important role in chaos control and synchronization.

Influence of Al3+doping on the energy levels and thermal property of the 3.5MgO·0.5MgF2·GeO2:Mn4+ red-emitting phosphor*

A series of Al3+ -doped 3.5MgO0.5MgF2GeO2:Mn4+ red-emitting phosphors is synthesized by high temperature solid-state reaction. The broad excitation band at 300 nm–380 nm, resulting from the 4A2 → 4T1 transition of Mn4+, exhibits a blue shift with the increase of Al2O3 content. The observation of the decreased Mn4+O2 − distance is explained by the crystal field theory. The temperature-dependent photoluminescence spectra with various amounts of Al2O3 content are comparatively measured and the calculation shows that the activation energy increases up to 0.41 eV at the Al2O3 content of 0.1 mol. The maximum phonon densities of state for these samples are calculated from Raman spectra and they are correlated with the thermal properties.

Preparation and control of entangled states in the two-mode coherent fields interacting with a moving atom via two-photon process

We investigate the preparation and the control of entangled states in a system with the two-mode coherent fields interacting with a moving two-level atom via the two-photon transition. We discuss entanglement properties between the two-mode coherent fields and a moving two-level atom by using the quantum reduced entropy, and those between the two-mode coherent fields by using the quantum relative entropy. In addition, we examine the influences of the atomic motion and field-mode structure parameter p on the quantum entanglement of the system. Our results show that the period and the duration of the prepared maximal atom-field entangled states and the frequency of maximal two-mode field entangled states can be controlled, and that a sustained entangled state of the two-mode field, which is independent of atomic motion and the evolution time, can be obtained, by choosing appropriately the parameters of atomic motion, field-mode structure, initial state and interaction time of the system.

Manipulation of Quantum Nonlocality of the Single-Photon Entangled State via Beam Splitter

Quantum nonlocality of the single-photon entangled state emerging from a beam splitter with arbitrary controlling parameters is investigated by means of the parity measurement. The condition of the maximal violation of the Bell-CHSH inequality is obtained for the single-photon entangled state. Under the condition of the small coherent intensity J (J = 0.1) and the phase difference γαβ of the two coherent displacements being opposite to the internal phase shift of the beam splitter (γαβ = −), we find that the quantum nonlocality depends only on the reflection coefficient R of the beam splitter, while plays an important role for selecting γαβ. The strongest quantum nonlocality can be observed for a 50:50 beam splitter. If R deviates from the intermediate value 0.5, the quantum nonlocality decreases gradually, even vanishes. Our results provide a method to observe and manipulate the quantum nonlocality of the single-photon entangled state by adjusting the parameters of the coherent displacements and the beam splitter.

Entangled states in the two-mode coherent fields interacting with a two-level atom

We investigate the entanglement properties of the two-mode coherent fields interacting with a two-level atom via the two-photon transition. We discuss the quantum entanglement between the two-mode coherent fields and the two-level atom by using the quantum reduced entropy and that between the two-mode coherent fields by using the quantum relative entropy. We also examine the influences of the initial states of the atom and the two-mode coherent fields on the quantum entanglement of the system. Our results show that three types of entangled states can be prepared via the two-mode coherent fields interacting with a two-level atom and choosing appropriately the initial-state parameters of the system.

Efficient Passively Q-Switched Nd:YAG/Cr4+:YAG/LBO Microchip Laser*

Performance of an LD-end-pumped passively Q-switched Nd:YAG/Cr4+:YAG microchip laser operating at 1123 nm is studied. A maximum average output power of 517 mW with an optical-to-optical conversion efficiency of 12.6% and a slope efficiency of 25.8% is obtained under a pump power of 4.1 W. A minimum pulse width of 1.1 ns with a pulse repetition rate of 20.2 kHz is obtained, and the corresponding pulse energy and peak power are 25.6 μJ and 23.3 kW, respectively. To our knowledge, the 23.3 kW peak power is the highest among 1123 nm lasers. Additionally, based on the 1123 nm laser, with LBO as the frequency doubler, a 288-mW green-yellow laser at 561 nm is successfully achieved.

Preparation of optimal entropy squeezing state of atomic qubit inside the cavity via two-photon process and manipulation of atomic qubit outside the cavity

Considering two atomic qubits initially in Bell states, we send one qubit into a vacuum cavity with two-photon resonance and leave the other one outside. Using quantum information entropy squeezing theory, the time evolutions of the entropy squeezing factor of the atomic qubit inside the cavity are discussed for two cases, i.e., before and after rotation and measurement of the atomic qubit outside the cavity. It is shown that the atomic qubit inside the cavity has no entropy squeezing phenomenon and is always in a decoherent state before the operating atomic qubit outside the cavity. However, the periodical entropy squeezing phenomenon emerges and the optimal entropy squeezing state can be prepared for the atomic qubit inside the cavity by adjusting the rotation angle, choosing the interaction time between the atomic qubit and the cavity, controlling the probability amplitudes of subsystem states. Its physical essence is cutting the entanglement between the atomic qubit and its environment, causing the atomic qubit inside the cavity to change from the initial decoherent state into maximum coherent superposition state, which is a possible way of recovering the coherence of a single atomic qubit in the noise environment.

Information Entropy Squeezing of a Two-Level Atom Interacting with Two-Mode Coherent Fields

From a quantum information point of view we investigate the entropy squeezing properties for a two-level atom interacting with the two-mode coherent fields via the two-photon transition. We discuss the influences of the initial state of the system on the atomic information entropy squeezing. Our results show that the squeezed component number, squeezed direction, and time of the information entropy squeezing can be controlled by choosing atomic distribution angle, the relative phase between the atom and the two-mode field, and the difference of the average photon number of the two field modes, respectively. Quantum information entropy is a remarkable precision measure for the atomic squeezing.

Entanglement Manipulation for a Two-Mode Squeezed Vacuum State

By numerically analysing the entropy of entanglement of the output state from a Mach–Zehnder interferometer for the two-mode squeezed vacuum state input, it is found that if the internal phase shift of the interferometer is adjusted to the value of 0 or π, the entangling characteristic of the input state is efficiently preserved at the output. If the internal phase shift is tuned to the value of π/2, the two-mode squeezed vacuum state is completely disentangled at the output of the setup. If the internal phase shift deviates from the above values, the input state is degraded into a partially entangled output state. Based on these results, a method for optically realizing the entanglement preservation, entanglement degradation, and disentanglement via the interferometer is obtained.