Liang Rui-Sheng

Analysis of performance and optimum configuration of two-stage semiconductor thermoelectric module

In this paper, the theoretical analysis and simulating calculation were conducted for a basic two-stage semiconductor thermoelectric module, which contains one thermocouple in the second stage and several thermocouples in the first stage. The study focused on the configuration of the two-stage semiconductor thermoelectric cooler, especially investigating the influences of some parameters, such as the current I1 of the first stage, the area A1 of every thermocouple and the number n of thermocouples in the first stage, on the cooling performance of the module. The obtained results of analysis indicate that changing the current I1 of the first stage, the area A1 of thermocouples and the number n of thermocouples in the first stage can improve the cooling performance of the module. These results can be used to optimize the configuration of the two-stage semiconductor thermoelectric module and provide guides for the design and application of thermoelectric cooler.

A High-Sensitivity Refractive-Index Sensor Based on Plasmonic Waveguides Asymmetrically Coupled with a Nanodisk Resonator*

A high-sensitivity plasmonic refractive-index sensor based on the asymmetrical coupling of two metal-insulator-metal waveguides with a nanodisk resonator is proposed and simulated in the finite-difference time domain. Both analytic and simulated results show that the resonance wavelengths of the sensor have an approximate linear relationship with the refractive index of the materials which are filled into the slit waveguides and the disk-shaped resonator. The working mechanism of this sensor is exactly due to the linear relationship, based on which the refractive index of the materials unknown can be obtained from the detection of the resonance wavelength. The measurement sensitivity can reach as high as 6.45 × 10−7, which is nearly five times higher than the results reported in the recent literature [Opt. Commun. 300 (2013) 265]. With an optimum design, the sensing value can be further improved, and it can be widely applied into the biological sensing. The sensor working for temperature sensing is also analyzed.

Multifunctional disk device for optical switch and temperature sensor

A multifunctional surface plasmon polariton disk device coupled by two metal?insulator?metal (MIM) waveguides is proposed and investigated numerically with finite-difference time-domain simulation. It can be used as optical switch and temperature sensor by filling disk with liquid crystal and ethanol, respectively. The simulation results demonstrate that the transmission characteristics of an optical switch can be manipulated by adjusting the radius of disk and the slit width between disk and MIM waveguides. The transmittance and modulation depth of optical switch at 1550?nm are up to 64.82% and 17.70?dB, respectively. As a temperature sensor, its figure of merit can reach 30.46. In this paper, an optical switch with better efficiency and a temperature sensor with better sensitivity can be achieved.

Decoherence of two-qubit system in a non-Markovian squeezed reservoir ⁄

The decoherence of two initially entangled qubits coupled with a squeezed vacuum cavity separately is investigated exactly. The results show that, first, in principle, the disentanglement time decreases with the increase of squeeze parameter r, due to the augmenting of average photon number of every mode in the squeezed vacuum cavity. Second, there appear entanglement revivals after the complete disentanglement for the case of even parity initial Bell state, while there occur the entanglement decrease and the entanglement revival before the complete disentanglement for the case of odd parity initial Bell state. The results are quite different from those for the case of qubits in a vacuum cavity.

Practical non-orthogonal decoy state quantum key distribution with heralded single photon source ⁄

Recently the performance of the quantum key distribution (QKD) is substantially improved by the decoy state method and the non-orthogonal encoding protocol, separately. In this paper, a practical non-orthogonal decoy state protocol with a heralded single photon source (HSPS) for QKD is presented. The protocol is based on 4 states with different intensities, i.e. one signal state and three decoy states. The signal state is for generating keys; the decoy states are for detecting the eavesdropping and estimating the fraction of single-photon and two-photon pulses. We have discussed three cases of this protocol, i.e. the general case, the optimal case and the special case. Moreover, the final key rate over transmission distance is simulated. For the low dark count of the HSPS and the utilization of the two-photon pulses, our protocol has a higher key rate and a longer transmission distance than any other decoy state protocol.

Generation of GHZ States via Deterministic Entanglement Concentration

We present the generation of six-particle Greenberger–Horne–Zeilinger (GHZ) states via deterministic entanglement concentration and generalize the scheme to the case of 2N particles. We show that arbitrary 2N-particle GHZ states can be obtained with certain probability via entanglement concentration. This may provide a new perspective for the preparation of multi-particle GHZ states. This study is also an exploration on the theory of deterministic entanglement concentration.

Concurrence evolution of two qubits coupled with one-mode cavity separately

The concurrence evolution of two qubits coupled with one-mode cavity separately is investigated exactly without adopting the rotating-wave approximation. The results show that for the resonant case, the concurrence evolution behaviour of the system is similar to that of the Markovian case when the coupling strength is weak, while the concurrence vanishes in a finite time and might revive fractional initial entanglement before it permanently vanishes when the coupling strength is strong. And for the detuning case, the entanglement could periodically recover after complete disentanglement. These results are quite different from those of system subjected to Jaynes–Cummings model.

The amplified model of erbium-doped fiber amplifier (EDFA) with cross-phase modulation (XPM)

Abstract Based on the rate equations and the power propagation equations, the amplified model is obtained which considers the cross-phase modulation (XPM)-induced intensity fluctuation between pump power and signal power in erbium-doped fiber amplifier (EDFA). Simulation results show: a higher nonlinear coefficient and a stronger pump power cause a stronger XPM in EDFA. Before the optimal length of EDF, the intensity caused by XPM increases with the increasing length, but after the optimal length, the XPM presents saturation. A bigger nonlinear coefficient γ corresponds to a smaller optimal length and gain, and makes gain saturation more easy. XPM effect will decrease EDFA’s amplified efficiency.

Influence of electron—phonon interaction on the properties of transport through double quantum dot with ferromagnetic leads

Electronic transport through a vibrating double quantum dot (DQD) in contact with noncollinear ferromagnetic (FM) leads is investigated. The state transition between the two dots of the DQD is excited by an AC microwave driving field. The corresponding currents and differential conductance are calculated in the Coulomb blockade regime by means of the Born—Markov master equation. It is shown that the interplay between electrons and phonons gives rise to phonon-assisted tunneling resonances and Franck—Condon blockade under certain conditions. In noncollinear magnetic configurations, spin-blockade effects are also observed, and the angle of polarization has some influence on the transport characteristics.

Experimental Study on Practical Quantum Key Distribution Scheme with Time-Multiplexed Technique

We present a scheme that is capable of detecting photon numbers during the quantum key distribution (QKD) based on an improved differential phase shift (DPS) system without Trojan horse attack. A time-multiplexed detector (TMD) is set in for the photon-number resolution. Two fibre loops are used for detecting photon numbers as well as distributing keys. The long-term stabilization is guaranteed by two Faraday mirrors (FM) at Bobs site to automatically compensate for polarization defect. Our experimental study (90km QKD is completed) indicates that such a system is stable and secure which nearly reaches the performance of a single photon scheme.