Scheme for Teleportation of Four-Level Atomic States in Thermal Cavities

We propose a scheme for teleportation of four-level atomic states in thermal cavities. The scheme does not involve the generalized Bell-state or generalized GHZ-state measurement, which is difficult in practice. Another feature of the scheme is that it does not require individual addressing of atoms in cavity and is insensitive to both cavity decay and thermal field, which is of importance in point of experiment.

System-Level EMC Assessment for Military Vehicular Communication Systems Based on a Modified Four-Level Assessment Model

With the development of EMC technology, EMC assessment has become increasingly important in EMC design. Although numerous EMC assessment models are available today, few of them can provide a tradeoff between efficiency and accuracy for the specific case of military vehicular communication systems. Face to this situation, a modified four-level assessment model is proposed in the paper. First, the development of EMC assessment technology is briefly reviewed, and the theoretical mechanism of EMI environment is introduced. Then, the architecture of the proposed model is outlined, and the assessment methods are explored. To demonstrate the application of it, an example involving a communication system in a military vehicle is presented. From the physical layer to the signal layer, a hierarchical assessment on the entire system is successfully performed based on the proposed model, and we can make a qualitative EMC assessment on the EMC performance of the system. Based on a comparison with the traditional model, we conclude that the proposed model is more accurate, more efficient and less time-consuming, which is suitable for the EMC assessment on militaryvehicular communication systems. We hope that the proposed model will serve as a useful reference for system-level EMC assessments for other systems.

Realization of Toffoli gate operation using four-level atoms in cavity QED system

This paper proposes a scheme for realization of a three-qubit Toffoli gate operation using three four-level atoms by a selective atom-field interaction in a cavity quantum electrodynamics system. In the proposed protocol, the quantum information is encoded on the stable ground states of atoms, and atomic spontaneous emission is negligible as the large atom-avity detuning effectively suppresses the spontaneous decay of the atoms. The influence of the dissipation on fidelity and success probability of the three-qubit Toffoli gate is also discussed. The scheme can also be applied to realize an N-qubit Toffoli gate and the interaction time required does not rise with increasing the number of qubits.

Influence of Doppler broadening and spontaneously generated coherence on propagation effect in a quasi lambda-type four-level system

In this paper we study influences of Doppler broadening, spontaneously generated coherence, and other system parameters on propagation effect in a quasi lambda-type four-level atomic system. It is shown that when the Doppler broadening is present, generally speaking, the values of gain and intensity of lasing without inversion （i.e. the probe field） in the co-propagating probe and driving fields case are much larger than those in the counter-propagating case; considerably larger gain and intensity of lasing without inversion than those without the Doppler broadening can be obtained by choosing appropriate values of the Doppler broadening width and spontaneously generated coherence strength. The gain and intensity of lasing without inversion increase with the increase of spontaneously generated coherence strength; when spontaneously generated coherence is present, much larger gain and intensity of lasing without inversion than those in the case without spontaneously generated coherence can be obtained. Choosing suitable values of the probe detuning, Rabi frequencies of the driving and pump fields at the entrance of the medium also can remarkably enhance the gain and intensity of lasing without inversion.

Selective Atom-Cavity Interaction Scheme for Quantum Controlled-NOT Gate Using Four-Level Atoms in Cavity QED System

We propose a scheme for realization a quantum Controlled-NOT gate operation using two four-level atoms through a selective atom cavity interaction in cavity quantum electrodynamics system. In our protocol, the quantum information is encoded on the stable ground states of the two atoms. During the interaction between atoms and single-mode vacuum cavity-field, the atomic spontaneous emission is negligible as the large atom-cavity detuning effectively suppresses the spontaneous decay of the atoms. The influences of the dissipation and the deviation of interaction time on fidelity and corresponding success probability of the quantum Controlled-NOT gate and the experimental feasibility of our proposal are also discussed.

Phase grating in a doubly degenerate four-level system

In this paper, we suggest a doubly degenerate four-level system, in which the transition takes place between the hyperfine energy 52S1/2 F = 1 and 52P3/2 F = 2 in rubidium 87 D2 line, for studying atomic phase grating based on the cross-Kerr and phase conjugation effects. The phase grating with high efficiency can be obtained by tuning phase shift Ф between the coupling and probe field, when the coupling intensity is much stronger than the strength of probe field. Under different coupling intensities, a high diffraction efficiency can be maintained. A new and simple way of implementing phase grating is presented. However, in such an atomic system, two main limitations must be taken into account. First, the independence between steady state probe susceptibility and the coupling intensity, when the population decay rate is larger than the Rabi frequency of the coupling field, cannot result in diffraction grating; second, the sample to be prepared should not be too long.

Fluorescence properties in a single driven four-level atomic system

The spontaneous emission decay dynamics of a tripod configuration four-level atom driven by a single laser field is studied. Under different initial conditions, we discuss the effects of quantum interference and detuning of external driving field on atomic spontaneous emission properties. For the larger detuning, the interesting phenomena of the spectral line narrowing are found which stem from the contribution of external driving field.

Four-Level Decay Model of^6P_(7/2) Excited State of Eu^(2+) Ion in KMgF_3

A four-level decay model of ~6P_(7/2) excited state of Eu^(2+_ ion in KMgF_3: Eu^(2+) has been proposed. The decay profiles of the ~6P_(7/2) excited state of Eu^(2+) are two exponential and the physical implication of each term in the fit equation responsible for the model is interpreted. The data obtained spectroscopically are in good agreement with the fit results.

the phase-dependent gain without inversion in a Doppler broadened open four-level system

It is shown that in a Doppler broadened open N-type four-level atomic system with spontaneously generated coherence （SGC）, the gain without inversion （GWI） is very sensitive to the variation of the relative phase between the probe field and the driving field; the atomic exit rate （R0） and the ratio （S） of the atomic injection rates have a considerable modulation effect on the phase-dependent GWI. GWI first increases and then decreases with R0 increasing; in a certain value range of S, GWI increases monotonically with S increasing; by adjusting the values of R0 and S, in an open system a much larger GWI can be obtained than in the corresponding closed system [2011 Phys. Rev. A 83 043805]. The modulation effects of R0 and S on the phase-dependent GWI in the case with the counter-propagating probe and driving fields are stronger than those in the co-propagating case, GWI in the co-propagating case is much larger than that in the counter-propagating case.

Four-level model of ion-ion laser-induced collisional energy transfer and numerical calculations for Ca^+-Sr^+ system

The four-level model of laser-induced collisional energy transfer （LICET） for the ion-ion collision system is established based on the time-dependent SchrSdinger equation for the electron dynamics, through which the equations of motion of the probability amplitudes and cross section of the collision system are obtained. Numerical calculations are performed for the Ca＋ Sr＋ system, with the results showing that the peak of the LICET spectrum appears at a resonant frequency of the transfer laser. The magnitude of the obtained collision cross section is in the order of 10-16 cm2, and is comparable to that obtained in atomic systems, which indicates the validity of the established four-level model.

Delay time dependence of wave packet motion and population transfer of four-level K_2 molecule in pump–pump–probe pulses

The effect of delay time on photoelectron spectra and state populations of a four-level ladder K2 molecule is investigated by a pump1–pump2–probe pulse via the time-dependent wave packet approach. The periodical motion of the wave packet leads to the periodical change of the photoelectron spectra. The Autler–Townes triple splitting appears at zero delay time, double splitting appears at nonzero delay time between pump1 and pump2 pulses, and no splitting appears at nonzero delay time between pump2 and probe pulses. The periodical change of the state populations with the delay time may be due to the coupling effect between the two pulses. It is found that the selectivity of the state populations may be attained by regulating the delay time. The results can provide an important basis for realizing the optical control of molecules experimentally.

Two-dimensional atom localization via probe absorption in a four-level atomic system

We have investigated the two-dimensional （2D） atom localization via probe absorption in a coherently driven four-level atomic system by means of a radio-frequency field driving a hyperfine transition. It is found that the detecting probability and precision of 2D atom localization can be significantly improved via adjusting the system parameters. As a result, our scheme may be helpful in laser cooling or the atom nano-lithography via atom localization.

Lasing without inversion in a four-level diamond system

We study the lasing without inversion in a four-level diamond configuration in the case of incoherent pumping field within the framework of the bare-state basis. With the strong fields limit, we obtain the approximate steady-state solution, and discuss the dependence of population distribution and system gain on probe detuning and auxiliary field Rabi frequency.

Electromagnetically Induced Self-Imaging in Four-Level Doppler Broadening Medium

We show the influences of temperature on the self-imaging in the coherent atomic system which consists of four-level 87Rb atoms. The different-direction self-imaging, the corresponding imaging quality, and the imaging contrast ratio in this Doppler broadening medium are studied. As a result, the imaging-position linearly increases with the temperature, while the quality of the self-imaging does not show clear connection with the temperature. Due to the weaker mutual interference in the higher temperature, the contrast ratios in the two directions increase. The interesting results are important and may have potential applications in imaging storage and processing.

Modulation of atomic exit and injection rates on the phase-dependent gain without inversion in a Doppler broadened open four-level system

It is shown that in a Doppler broadened open N-type four-level atomic system with spontaneously generated coherence (SGC), the gain without inversion (GWI) is very sensitive to the variation of the relative phase between the probe field and the driving field; the atomic exit rate (R0) and the ratio (S) of the atomic injection rates have a considerable modulation effect on the phase-dependent GWI. GWI first increases and then decreases with R0 increasing; in a certain value range of S, GWI increases monotonically with S increasing; by adjusting the values of R0 and S, in an open system a much larger GWI can be obtained than in the corresponding closed system [2011 Phys. Rev. A 83 043805]. The modulation effects of R0 and S on the phase-dependent GWI in the case with the counter-propagating probe and driving fields are stronger than those in the co-propagating case, GWI in the co-propagating case is much larger than that in the counter-propagating case.

Low-complexity model predictive control of a four-level active neutral point clamped inverter without weighting factors

The four-level active neutral point clamped(ANPC)inverter has become increasingly widely used in the renewable energy indus-try since it offers one more voltage level without increasing the total number of active switches compared to the three-level ANPC inverter.The model predictive current control(MPCC)is a promising control method for multi-level inverters.However,the conven-tional MPCC suffers from high computational complexity and tedious weighting factor tuning in multi-level inverter applications.A low-complexity MPCC without weighting factors for a four-level ANPC inverter is proposed in this paper.The computational burden and voltage vector candidate set are reduced according to the relationship between voltage vector and neutral point voltage balance.The proposed MPCC shows excellent steady-state and dynamics performances while ensuring the neutral point voltage balancing.The efficacy of the proposed MPCC is verified by simulation and experimental results.

神经外科重症患者四级康复护理活动方案的构建及应用

目的构建神经外科重症患者四级康复护理活动方案并评价其应用效果。方法选取2020-08—12北京市某三级甲等医院神经外科ICU收治的96例患者为试验组,患者入住ICU≥24 h且病情稳定后,根据其意识和肌力评估情况,实施四级康复护理活动方案。选取2020-03—07神经外科ICU收治的99例患者为对照组,给予常规康复护理。比较2组患者的康复状况及并发症发生情况。结果试验组机械通气时间[11(5,17)d比16(7,24)d]、ICU住院时间[13(7,25)d比20(12,30)d]、住院费用[137070(76603,219237)元比193839(129781,321362)元]和出ICU的APACHE-Ⅱ评分[(22.03±7.54)分比(25.21±6.51)分]均低于对照组(P<0.05),出院ADL评分[5(0,15)分比0(0,10)分]高于对照组(P<0.05)。在肺部感染[40(41.67%)比57(57.57%)]和下肢深静脉血栓[3(3.13%)比25(25.25%)]方面,试验组均低于对照组,差异有统计学意义(P<0.05);在ICU谵妄和压力性损伤方面,2组差异无统计学意义(P>0.05)。结论对神经外科重症患者实施四级康复护理活动方案能够改善重症患者的恢复状况,减少并发症的发生,有助于促进重症患者早期康复。

Quantum key distribution using four-level particles

We present a quantum key distribution protocol based on four-level particle entanglement.Furthermore,a controlled quantum key distribution protocol is proposed using three four-level particles.We show that the two protocols are secure.

Comparison of the anterior and posterior approach in treating four-level cervical spondylotic myelopathy

Background:The optimal surgical approach for four-level cervical spondylotic myelopathy remains controversial.The purpose of this study was to compare clinical and radiological outcomes and complications between the anterior and posterior approaches for four-level cervical spondylotic myelopathy.Methods:A total of 19 patients underwent anterior decompression and fusion and 25 patients underwent posterior laminoplasty and instrumentation in this study.Perioperative information,intraoperative blood loss,clinical and radiological outcomes,and complications were recorded.Japanese Orthopedic Association(JOA)score,36-item short form survey(SF-36)score and cervical alignment were assessed.Results:There were no significant differences in JOA scores between the anterior and posterior group preoperatively(11.6±1.6 vs.12.1±1.5),immediately postoperatively(14.4±1.1 vs.13.8±1.3),or at the last follow-up(14.6±1.0 vs.14.2±1.1)(P>0.05).The JOA scores significantly improved immediately postoperatively and at the last follow-up in both groups compared with their preoperative values.The recovery rate was significantly higher in the anterior group both immediately postoperatively and at the last follow-up.The SF-36 score was significantly higher in the anterior group at the last follow-up compared with the preoperative value(69.4 vs.61.7).Imaging revealed that there was no significant difference in the Cobb angle at C2-C7 between the two groups preoperatively(-2.0°±7.3°vs.-1.4°±7.5°).The Cobb angle significantly improved immediately postoperatively(12.3°±4.2°vs.9.2°±3.6°)and at the last follow-up(12.4°±3.5°vs.9.0°±2.6°)in both groups compared with their preoperative values(P=0.00).Three patients had temporary dysphagia in the anterior group and four patients had persistent axial symptoms in the posterior group.Conclusions:Both the anterior and posterior approaches were effective in treating four-level cervical spondylotic myelopathy in terms of neurological clinical outcomes and radiological features.However,the JOA score recovery rate and SF-36 score in the anterior group were significantly higher.Persistent axial pain could be a major concern when undertaking the posterior approach.

Realization of population inversion between 7S_(1/2) and 6P_(3/2) levels of cesium for four-level active optical clock

We demonstrate experimentally the population inversion between 7S1/2 and 6P3/2 levels of cesium in thermal cesium cell with a 455.5 nm pumping laser.We calculate the relative population probabilities at each level theoretically with the density matrix method.In a steady state,5.8% atoms are at 7S1/2 level and 2.9% at 6P3/2 level,which builds up the population inversion between the two levels.We obtain the fluorescence spectra produced in thermal cesium cell in our experiment.The measured relative intensity of each available fluorescence spectral line in the experiment agrees very well with the theoretical result.The demonstrated population inversion between 7S1/2 and 6P3/2 levels can be used to construct an active optical clock of four-level system with a wavelength of 1469.9 nm.