Due to the spatial characteristics of orbital angular momentum,vortex fields can be applied in the fields of quantum storage and quantum information.We study the realization of spatially modulated vortex fields based ...Due to the spatial characteristics of orbital angular momentum,vortex fields can be applied in the fields of quantum storage and quantum information.We study the realization of spatially modulated vortex fields based on four-wave mixing in a four-level atomic system with a diamond structure.The intensity and spiral phase of the vortex field are effectively transferred to the generated four-wave mixing field.By changing the detuning of the probe field,the phase and intensity of the generated vertex four-wave mixing field can be changed.When the probe field takes a large detuning value,the spatial distribution of the intensity and phase of the vertex four-wave mixing field can be effectively tuned by adjusting the Rabi frequency or detuning value of the coupled field.At the same time,we also provide a detailed explanation based on the dispersion relationship,and the results agree well with our simulation results.展开更多
Focusing on the mechanism of interfa-cial exciton dissociation in edge-on stacked ZnPc-F_(8)ZnPc aggregate,we employ the fragment particle-hole densities(FPHD)method to con-struct the Hamiltonian of diabatic states an...Focusing on the mechanism of interfa-cial exciton dissociation in edge-on stacked ZnPc-F_(8)ZnPc aggregate,we employ the fragment particle-hole densities(FPHD)method to con-struct the Hamiltonian of diabatic states and use the non-Markovian stochastic Schrödinger equation(NMSSE)to simulate the photo-in-duced dynamics processes.The re-sults show that aggregation effects have a significant impact on the interfacial exciton dissociation process.After photo-excita-tion,the excitons first preferentially delocalize and perform the charge transfer(CT)states in the pure ZnPc or F_(8)ZnPc aggregates within 100 fs.These‘intramolecular’CT states can easi-ly evolve into interfacial CT states by hopping electrons and holes in the intramolecular CT states across the interface.Compared with these exciton dissociation processes,the direct ex-citon dissociation into interfacial CT state is relatively slow due to the small electronic cou-pling and vibrational coherence between the locally excited state and the interfacial CT state.As the temperature rises and the vibronic coherence weakens,the direct dissociation rates are significantly enhanced.This investigation provides valuable insights for the design and opti-mization of high-performance organic photovoltaic devices.展开更多
We demonstrate a triple-pass scheme for coherent transfer of optical frequency and the delay effect on the fiber phase noise compensation. It is theoretically proved that the delay effect consists of both fiber delay ...We demonstrate a triple-pass scheme for coherent transfer of optical frequency and the delay effect on the fiber phase noise compensation. It is theoretically proved that the delay effect consists of both fiber delay and servo delay. The delay effect confines the servo bandwidth within 1/8 and induces a residual fiber phase noise after noise compensation. For a 25-km-long fiber, the servo bandwidth is found to be around 1 k Hz, and the fiber phase noise is suppressed approaching to the theoretical limitation. The triple-pass scheme enables the simultaneous transfer of optical frequency to multiple remote users. The performance of noise compensator in the triple-pass scheme can achieve a similar level result compared with that in the double-pass scheme.展开更多
A pocket coherent population trapping（CPT） atomic magnetometer scheme that uses a vertical cavity surface emitting laser as a light source is proposed and experimentally investigated.Using the differential detecting...A pocket coherent population trapping（CPT） atomic magnetometer scheme that uses a vertical cavity surface emitting laser as a light source is proposed and experimentally investigated.Using the differential detecting magneto–optic rotation effect,a CPT spectrum with the background canceled and a high signal-to-noise ratio is obtained.The experimental results reveal that the sensitivity of the proposed scheme can be improved by half an order,and the ability to detect weak magnetic fields is extended one-fold.Therefore,the proposed scheme is suited to realize a pocket-size CPT magnetometer.展开更多
The velocity ratio of a free shear layer has an important influence on the spatial development of the large scale coherent structures in the layer. In this study, numerical simulations are performed to get an insight ...The velocity ratio of a free shear layer has an important influence on the spatial development of the large scale coherent structures in the layer. In this study, numerical simulations are performed to get an insight into this problem. The obtained numerical results agree quite well with those of a linear inviscid stability theory and the available experimental data.展开更多
A generalized scheme for the construction of coherent states in the context of position-dependent effective mass systems has been presented. This formalism is based on the ladder operators and associated algebra of th...A generalized scheme for the construction of coherent states in the context of position-dependent effective mass systems has been presented. This formalism is based on the ladder operators and associated algebra of the system which are obtained using the concepts of supersymmetric quantum mechanics and the property of shape invariance. In order to exemplify the general results and to analyze the properties of the coherent states, several examples have been considered.展开更多
The electroencephalogram(EEG)rhythm and functional near-infrared spectroscopy(fNIRS)activation levels have not been compared between a healthy control group(HCG)and methamphetamine user group(MUG)with different addict...The electroencephalogram(EEG)rhythm and functional near-infrared spectroscopy(fNIRS)activation levels have not been compared between a healthy control group(HCG)and methamphetamine user group(MUG)with different addiction histories.This study used 64-electrode EEG and fNIRS to conduct an experiment that analyzed the resting and craving states.The EEG and fNIRS data of 56 participants were collected,including 14 healthy participants,14 methamphetamine users with an addiction history of 0.5–5 years,14 users with an addiction history of 5–10 years,and 14 users with an addiction history of 10–15 years.Isolated effective coherence(iCoh)within the brain network was used to process the EEG data.Statistical analysis was performed to compare differences in iCoh among the delta,theta,alpha,beta,and gamma bands and explore oxyhemoglobin activation levels in the ventrolateral prefrontal cortex,dorsolateral prefrontal cortex,orbitofrontal cortex,and frontopolar prefrontal cortex(FPC)of the control group.Finally,the Kmeans,Gaussian mixed model(GMM),linear discriminant analysis(LDA),support vector machine(SVM),Bayes,and convolutional neural networks(CNN)algorithms were used to classify methamphetamine users based on drug and neutral images.A 3-class accuracy was achieved.Changes in EEG and fNIRS activation levels of HCG and MUG with varied addiction histories were demonstrated.展开更多
We present a cooling scheme with a tripod configuration atomic ensemble trapped in an optomechanical cavity.With the employment of two different quantum interference processes,our scheme illustrates that it is possibl...We present a cooling scheme with a tripod configuration atomic ensemble trapped in an optomechanical cavity.With the employment of two different quantum interference processes,our scheme illustrates that it is possible to cool a resonator to its ground state in the strong cavity-atom coupling regime.Moreover,with the assistance of one additional energy level,our scheme takes a larger cooling rate to realize the ground state cooling.In addition,this scheme is a feasible candidate for experimental applications.展开更多
Bell’s theorem states that quantum mechanics cannot be accounted for by any local theory. One of the examples is the existence of quantum non-locality is essentially violated by the local Bell’s inequality. Therefor...Bell’s theorem states that quantum mechanics cannot be accounted for by any local theory. One of the examples is the existence of quantum non-locality is essentially violated by the local Bell’s inequality. Therefore, the violation of Bell’s inequality(BI) has been regarded as one of the robust evidences of quantum mechanics. Until now, BI has been tested by many experiments, but the maximal violation(i.e., Cirel’son limit) has never been achieved. By improving the design of entangled sources and optimizing the measurement settings, in this work we report the stronger violations of the Clauser–Horne–Shimony–Holt(CHSH)-type Bell’s inequality. The biggest value of Bell’s function in our experiment reaches √to a significant one: S = 2.772 ± 0.063, approaching to the so-called Cirel’son limit in which the Bell function value is S = 22.Further improvement is possible by optimizing the entangled-photon sources.展开更多
An increasing amount of evidence indicates that lunar water ice exists in permanently shadowed regions at the poles and will soon become an important resource for lunar exploration.However,the water ice content and di...An increasing amount of evidence indicates that lunar water ice exists in permanently shadowed regions at the poles and will soon become an important resource for lunar exploration.However,the water ice content and distribution are still uncertain.We report a new 70-cm-wavelength radar image of the lunar south pole obtained by an Earth-based bistatic radar system consisting of the Sanya incoherent scatter radar(SYISR)and the five-hundred-meter aperture spherical radio telescope(FAST).The upper limit of water ice content(0 wt.%–6 wt.%)and its potential distribution are determined from a radar circular polarization ratio(CPR)map by considering the coherent backscatter opposition effect(CBOE)of water ice and ignoring the contribution of roughness to the CPR.This result is advantageous for future lunar exploration missions.展开更多
Photonic moirélattices(PMLs),with unique twisted periodic patterns,provide a valuable platform for investigating strongly correlated materials,unconventional superconductivity,and the localization–delocalization...Photonic moirélattices(PMLs),with unique twisted periodic patterns,provide a valuable platform for investigating strongly correlated materials,unconventional superconductivity,and the localization–delocalization transition.However,PMLs created either by the misorientation between lattice layers or by twisted van der Waals materials are typically non-tunable and inherently possess immutable refractive indices.Unlike those in the moirélattices of twisted two-dimensional materials,our work reports a moirélattice formed by overlapping two identical sublattices with twisted angles in an ultracold atomic ensemble.This photoinduced moirélattice with two twisted sublattices exhibits high flexibility and rich periodicity through adjustable twisted angles.Our results indicate that both the absorption/dispersion coefficients and the transmission of the photoinduced moirélattices can be effectively tuned by photon detuning and Rabi frequency,resulting in amplitude-and phase-type moirélattices.Based on the Fraunhofer diffraction theory,we have demonstrated that the far-field diffraction efficiency can be adjusted via altering photon detuning,and the rotation angle serves as a control knob for modulating the diffracted intensity distribution,thereby optimizing the performance of the photonic lattice.It is also found that the operation domains of the moirélattices with different rotation angles remain consistent,allowing for seamless conversion between various moiréperiod structures.Furthermore,a moirélattice composed of three twisted sublattices is investigated,revealing that the diffraction energy is uniformly dispersed in a circular distribution,which provides excellent agility in the design of optical devices.Such tunable PML offer a powerful tool for studying light propagation control and the intriguing physics of twisted systems in atomic media.展开更多
Using numerical simulations, the nonlinear transmission performance of polarization-division-multiplexed quadrature-phase-shift-keying （PDM-QPSK） coherent systems is studied. It is found that inter-channel cross-pol...Using numerical simulations, the nonlinear transmission performance of polarization-division-multiplexed quadrature-phase-shift-keying （PDM-QPSK） coherent systems is studied. It is found that inter-channel cross-polarization modulation （XPolM） induced nonlinear polarization scattering can significantly degrade the transmission performance of PDM-QPSK coherent systems and change the perspective of dispersion management in optical coherent transmission systems. Some techniques to mitigate nonlinear polarization scattering in dispersion-managed PDM coherent transmission systems are discussed, including the use of time-interleaved return-to-zero （RZ） PDM formats, the use of periodic-group-delay PGD dispersion compensators, and the judicious addition of some polarization-mode-dispersion （PMD） in the transmission link. It is shown that if nonlinear polarization scattering can be well mitigated, a polarization multiplexed optical coherent transmission system with dispersion management could perform better than that without it.展开更多
There are many examples that fluid flows on rough wall, such as channel flow in nature, pipe flow, etc. In order to know the flow structure of real fluids, it is important to study the effects of wall roughness on coh...There are many examples that fluid flows on rough wall, such as channel flow in nature, pipe flow, etc. In order to know the flow structure of real fluids, it is important to study the effects of wall roughness on coherent structure in turbulent shear flows. The experiments were carried out in a square glass channel, which is 600cm long, with the cross section of 30×25cm^2. The flow velocity was varied from 2 to 40 cm/s. Uniform sands whose diameters were 0.0012cm, 0.2gcm, 0.385cm, 0.594cm and 0.896cm respectively were glued to the floor of the channel. The rough Reynolds number Re_Δ= U_*Δ/ν=0.04～73, where U_*is the shear velocity, Δ is the diame- ter of uniform sand, v is the kinematic viscosity coefficient. Hydrogen bubble technique for flow visualization and HWL-II hot-film anemometer for velocity mea- surement were used in the experiments.展开更多
Linewidth narrowing and other quantum coherent effects based on three-photon coherent population trapping （CPT） in Ca＋ ions are investigated. If the propagation directions of the three lasers obey the phase matchin...Linewidth narrowing and other quantum coherent effects based on three-photon coherent population trapping （CPT） in Ca＋ ions are investigated. If the propagation directions of the three lasers obey the phase matching condition, the dark linewidth resulting from the CPT can be very narrow, and it can be controlled by adjusting the parameters of the lasers.展开更多
A periodic layered medium, with unit cells consisting of a dielectric and an electromagnetically-induced transparency （EIT）-based atomic vapor, is designed for light propagation manipulation. Considering that a dest...A periodic layered medium, with unit cells consisting of a dielectric and an electromagnetically-induced transparency （EIT）-based atomic vapor, is designed for light propagation manipulation. Considering that a destructive quantum interference relevant to a two-photon resonance emerges in EIT-based atoms interacting with both control and probe fields, an EIT-based periodic layered medium exhibits a flexible frequency-sensitive optical response, where a very small variation in the probe frequency can lead to a drastic variation in reflectance and transmittance. The present EIT-based periodic layered structure can result in controllable optical processes that depend sensitively on the external control field. The tunable and sensitive optical response induced by the quantum interference of a multi-level atomic system can be applied in the fabrication of new photonic and quantum optical devices. This material will also open a good perspective for the application of such designs in several new fields, including photonic microcircuits or integrated optical circuits.展开更多
The optical Bloch oscillation(OBO)is an optical-quantum analogy effect that is significant for light field manipulations,such as light beam localization,oscillation and tunneling.As an intra-band oscillation,OBO was i...The optical Bloch oscillation(OBO)is an optical-quantum analogy effect that is significant for light field manipulations,such as light beam localization,oscillation and tunneling.As an intra-band oscillation,OBO was important for optical investigations in photonic lattices and atomic vapors over an extended period of time.However,OBO in reconfigurable platforms is still an open topic,even though tunability is highly desired in developing modern photonic techniques.Here we theoretically establish and experimentally demonstrate OBO in an electromagnet-ically induced photonic lattice with a ramping refractive index,established in a coherently-prepared three-level 85 Rb atomic vapor under the electromagnetically induced transparency condition.This is achieved by interfering two coupling beams with Gaussian profiles and launching a probe beam that exhibits OBO within the resulting lattice.The induced reconfigurable photonic lattice possesses a transverse gradient,due to the innate edges of Gaussian beams,and sets a new stage for guiding the flow of light in periodic photonic environments.Our results should motivate better understanding of peculiar physical properties of an intriguing quantum-optical analogy in an atomic setting.展开更多
基金Project supported by the National Natural Science Foundation of China (Grant Nos.11704151 and 11247201)the Twelfth Five-year Program for Science and Technology of Education Department of Jilin Province (Grant No.20150215)。
文摘Due to the spatial characteristics of orbital angular momentum,vortex fields can be applied in the fields of quantum storage and quantum information.We study the realization of spatially modulated vortex fields based on four-wave mixing in a four-level atomic system with a diamond structure.The intensity and spiral phase of the vortex field are effectively transferred to the generated four-wave mixing field.By changing the detuning of the probe field,the phase and intensity of the generated vertex four-wave mixing field can be changed.When the probe field takes a large detuning value,the spatial distribution of the intensity and phase of the vertex four-wave mixing field can be effectively tuned by adjusting the Rabi frequency or detuning value of the coupled field.At the same time,we also provide a detailed explanation based on the dispersion relationship,and the results agree well with our simulation results.
基金supported by the National Natural Science Foundation of China(Nos.22033006,22173074,22473091, 92372105).
文摘Focusing on the mechanism of interfa-cial exciton dissociation in edge-on stacked ZnPc-F_(8)ZnPc aggregate,we employ the fragment particle-hole densities(FPHD)method to con-struct the Hamiltonian of diabatic states and use the non-Markovian stochastic Schrödinger equation(NMSSE)to simulate the photo-in-duced dynamics processes.The re-sults show that aggregation effects have a significant impact on the interfacial exciton dissociation process.After photo-excita-tion,the excitons first preferentially delocalize and perform the charge transfer(CT)states in the pure ZnPc or F_(8)ZnPc aggregates within 100 fs.These‘intramolecular’CT states can easi-ly evolve into interfacial CT states by hopping electrons and holes in the intramolecular CT states across the interface.Compared with these exciton dissociation processes,the direct ex-citon dissociation into interfacial CT state is relatively slow due to the small electronic cou-pling and vibrational coherence between the locally excited state and the interfacial CT state.As the temperature rises and the vibronic coherence weakens,the direct dissociation rates are significantly enhanced.This investigation provides valuable insights for the design and opti-mization of high-performance organic photovoltaic devices.
基金Supported by the National Natural Science Foundation of China under Grant No 61378037the Fundamental Research Funds for the Central Universities under Grant No JUSRP51628B
文摘We demonstrate a triple-pass scheme for coherent transfer of optical frequency and the delay effect on the fiber phase noise compensation. It is theoretically proved that the delay effect consists of both fiber delay and servo delay. The delay effect confines the servo bandwidth within 1/8 and induces a residual fiber phase noise after noise compensation. For a 25-km-long fiber, the servo bandwidth is found to be around 1 k Hz, and the fiber phase noise is suppressed approaching to the theoretical limitation. The triple-pass scheme enables the simultaneous transfer of optical frequency to multiple remote users. The performance of noise compensator in the triple-pass scheme can achieve a similar level result compared with that in the double-pass scheme.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11304362 and 61434005)
文摘A pocket coherent population trapping（CPT） atomic magnetometer scheme that uses a vertical cavity surface emitting laser as a light source is proposed and experimentally investigated.Using the differential detecting magneto–optic rotation effect,a CPT spectrum with the background canceled and a high signal-to-noise ratio is obtained.The experimental results reveal that the sensitivity of the proposed scheme can be improved by half an order,and the ability to detect weak magnetic fields is extended one-fold.Therefore,the proposed scheme is suited to realize a pocket-size CPT magnetometer.
基金Project supported by the National Natural Science Foundation of china
文摘The velocity ratio of a free shear layer has an important influence on the spatial development of the large scale coherent structures in the layer. In this study, numerical simulations are performed to get an insight into this problem. The obtained numerical results agree quite well with those of a linear inviscid stability theory and the available experimental data.
文摘A generalized scheme for the construction of coherent states in the context of position-dependent effective mass systems has been presented. This formalism is based on the ladder operators and associated algebra of the system which are obtained using the concepts of supersymmetric quantum mechanics and the property of shape invariance. In order to exemplify the general results and to analyze the properties of the coherent states, several examples have been considered.
基金supported by Shanghai Municipal Science and Technology Plan Project(No.22010502400)National Natural Science Foundation of China(Nos.82072228,92048205,and 62376149).
文摘The electroencephalogram(EEG)rhythm and functional near-infrared spectroscopy(fNIRS)activation levels have not been compared between a healthy control group(HCG)and methamphetamine user group(MUG)with different addiction histories.This study used 64-electrode EEG and fNIRS to conduct an experiment that analyzed the resting and craving states.The EEG and fNIRS data of 56 participants were collected,including 14 healthy participants,14 methamphetamine users with an addiction history of 0.5–5 years,14 users with an addiction history of 5–10 years,and 14 users with an addiction history of 10–15 years.Isolated effective coherence(iCoh)within the brain network was used to process the EEG data.Statistical analysis was performed to compare differences in iCoh among the delta,theta,alpha,beta,and gamma bands and explore oxyhemoglobin activation levels in the ventrolateral prefrontal cortex,dorsolateral prefrontal cortex,orbitofrontal cortex,and frontopolar prefrontal cortex(FPC)of the control group.Finally,the Kmeans,Gaussian mixed model(GMM),linear discriminant analysis(LDA),support vector machine(SVM),Bayes,and convolutional neural networks(CNN)algorithms were used to classify methamphetamine users based on drug and neutral images.A 3-class accuracy was achieved.Changes in EEG and fNIRS activation levels of HCG and MUG with varied addiction histories were demonstrated.
基金Project supported by the National Key Research and Development Program of China(Grant No.2017YFA0304503)Key Research and Development Project of Guangdong Province,China(Grant No.2020B030300001)the National Natural Science Foundation of China(Grant Nos.828330256,11636220,11805279,1173401,and 11504430)。
文摘We present a cooling scheme with a tripod configuration atomic ensemble trapped in an optomechanical cavity.With the employment of two different quantum interference processes,our scheme illustrates that it is possible to cool a resonator to its ground state in the strong cavity-atom coupling regime.Moreover,with the assistance of one additional energy level,our scheme takes a larger cooling rate to realize the ground state cooling.In addition,this scheme is a feasible candidate for experimental applications.
基金supported by the National Natural Science Foundation of China(Grant Nos.61308008,91321104,U1330201,and 11174373)the Fundamental Research Funds for the Central Universities(Grant No.2682014CX081)
文摘Bell’s theorem states that quantum mechanics cannot be accounted for by any local theory. One of the examples is the existence of quantum non-locality is essentially violated by the local Bell’s inequality. Therefore, the violation of Bell’s inequality(BI) has been regarded as one of the robust evidences of quantum mechanics. Until now, BI has been tested by many experiments, but the maximal violation(i.e., Cirel’son limit) has never been achieved. By improving the design of entangled sources and optimizing the measurement settings, in this work we report the stronger violations of the Clauser–Horne–Shimony–Holt(CHSH)-type Bell’s inequality. The biggest value of Bell’s function in our experiment reaches √to a significant one: S = 2.772 ± 0.063, approaching to the so-called Cirel’son limit in which the Bell function value is S = 22.Further improvement is possible by optimizing the entangled-photon sources.
基金supported by the National Natural Science Foundation of China(42425403,62227901,and 42241151)the Project of Stable Support for Youth Team in Basic Research Field,CAS(YSBR-018)+2 种基金the Guizhou Provincial Science and Technology Projects(QKHFQ[2023]003 and QKHPTRC-ZDSYS[2023]003)the Meridian ProjectShuai Li for data support。
文摘An increasing amount of evidence indicates that lunar water ice exists in permanently shadowed regions at the poles and will soon become an important resource for lunar exploration.However,the water ice content and distribution are still uncertain.We report a new 70-cm-wavelength radar image of the lunar south pole obtained by an Earth-based bistatic radar system consisting of the Sanya incoherent scatter radar(SYISR)and the five-hundred-meter aperture spherical radio telescope(FAST).The upper limit of water ice content(0 wt.%–6 wt.%)and its potential distribution are determined from a radar circular polarization ratio(CPR)map by considering the coherent backscatter opposition effect(CBOE)of water ice and ignoring the contribution of roughness to the CPR.This result is advantageous for future lunar exploration missions.
基金supported by the National Natural Science Foundation of China(NSFC)(Grant Nos.62074127,U21A2073,62304173,62304175,62404177,61804122,11874142,61627812,61705176,11874102,11474048,and 61805068)the Natural Science Fund of Shaanxi Province(Grant Nos.2018JQ6002,2021JQ062,2021JQ056,and 2021GY223)+4 种基金the Postdoctoral Science Foundation(Grant Nos.2019M653637,2019M660256,and 2017M620300)the National Key Research and Development Program of China(Grant No.2018YFE0125900)the Fundamental Research Funds for the Central Universities(FRFCU)(Grant No.ZYGX2019J102)the National Key R&D Program of China(NK R&D PC)(Grant Nos.2021YFB3602100,2017YFB0402800,and 2017YFB0402802)the Natural Science Basic Research Program of Shaanxi Province(Grant No.2024JC-YBMS-505).
文摘Photonic moirélattices(PMLs),with unique twisted periodic patterns,provide a valuable platform for investigating strongly correlated materials,unconventional superconductivity,and the localization–delocalization transition.However,PMLs created either by the misorientation between lattice layers or by twisted van der Waals materials are typically non-tunable and inherently possess immutable refractive indices.Unlike those in the moirélattices of twisted two-dimensional materials,our work reports a moirélattice formed by overlapping two identical sublattices with twisted angles in an ultracold atomic ensemble.This photoinduced moirélattice with two twisted sublattices exhibits high flexibility and rich periodicity through adjustable twisted angles.Our results indicate that both the absorption/dispersion coefficients and the transmission of the photoinduced moirélattices can be effectively tuned by photon detuning and Rabi frequency,resulting in amplitude-and phase-type moirélattices.Based on the Fraunhofer diffraction theory,we have demonstrated that the far-field diffraction efficiency can be adjusted via altering photon detuning,and the rotation angle serves as a control knob for modulating the diffracted intensity distribution,thereby optimizing the performance of the photonic lattice.It is also found that the operation domains of the moirélattices with different rotation angles remain consistent,allowing for seamless conversion between various moiréperiod structures.Furthermore,a moirélattice composed of three twisted sublattices is investigated,revealing that the diffraction energy is uniformly dispersed in a circular distribution,which provides excellent agility in the design of optical devices.Such tunable PML offer a powerful tool for studying light propagation control and the intriguing physics of twisted systems in atomic media.
文摘Using numerical simulations, the nonlinear transmission performance of polarization-division-multiplexed quadrature-phase-shift-keying （PDM-QPSK） coherent systems is studied. It is found that inter-channel cross-polarization modulation （XPolM） induced nonlinear polarization scattering can significantly degrade the transmission performance of PDM-QPSK coherent systems and change the perspective of dispersion management in optical coherent transmission systems. Some techniques to mitigate nonlinear polarization scattering in dispersion-managed PDM coherent transmission systems are discussed, including the use of time-interleaved return-to-zero （RZ） PDM formats, the use of periodic-group-delay PGD dispersion compensators, and the judicious addition of some polarization-mode-dispersion （PMD） in the transmission link. It is shown that if nonlinear polarization scattering can be well mitigated, a polarization multiplexed optical coherent transmission system with dispersion management could perform better than that without it.
文摘There are many examples that fluid flows on rough wall, such as channel flow in nature, pipe flow, etc. In order to know the flow structure of real fluids, it is important to study the effects of wall roughness on coherent structure in turbulent shear flows. The experiments were carried out in a square glass channel, which is 600cm long, with the cross section of 30×25cm^2. The flow velocity was varied from 2 to 40 cm/s. Uniform sands whose diameters were 0.0012cm, 0.2gcm, 0.385cm, 0.594cm and 0.896cm respectively were glued to the floor of the channel. The rough Reynolds number Re_Δ= U_*Δ/ν=0.04～73, where U_*is the shear velocity, Δ is the diame- ter of uniform sand, v is the kinematic viscosity coefficient. Hydrogen bubble technique for flow visualization and HWL-II hot-film anemometer for velocity mea- surement were used in the experiments.
基金Acknowledgements We thank Prof. Yi-fu Zhu for useful discus- sion. This work was supported by the National Basic Research Pro- gram of China （Grant No. 2005CB724502）, the National Natural Science Foundation of China （Grant Nos. 10874205 and 10774161） and the Chinese Academy of Sciences.
文摘Linewidth narrowing and other quantum coherent effects based on three-photon coherent population trapping （CPT） in Ca＋ ions are investigated. If the propagation directions of the three lasers obey the phase matching condition, the dark linewidth resulting from the CPT can be very narrow, and it can be controlled by adjusting the parameters of the lasers.
基金supported by the Taiwan Science Council (Nos.NSC 99-2811-M-216-001 and NSC 99-2112-M-216-002)the National Natural Science Foundation of China (Nos.60990320 and 60990322)+1 种基金the Natural Science Foundation of Zhejiang Province in China (No.Y6100280)the Fundamental Research Funds for the Central Universities of China
文摘A periodic layered medium, with unit cells consisting of a dielectric and an electromagnetically-induced transparency （EIT）-based atomic vapor, is designed for light propagation manipulation. Considering that a destructive quantum interference relevant to a two-photon resonance emerges in EIT-based atoms interacting with both control and probe fields, an EIT-based periodic layered medium exhibits a flexible frequency-sensitive optical response, where a very small variation in the probe frequency can lead to a drastic variation in reflectance and transmittance. The present EIT-based periodic layered structure can result in controllable optical processes that depend sensitively on the external control field. The tunable and sensitive optical response induced by the quantum interference of a multi-level atomic system can be applied in the fabrication of new photonic and quantum optical devices. This material will also open a good perspective for the application of such designs in several new fields, including photonic microcircuits or integrated optical circuits.
基金This work was supported by National Key R&D Program of China(Grants No.2018YFA0307500,2017YFA0303703)National Natural Science Foundation of China(Grants No.62022066,12074306,61975159,and 12074308)Work in Qatar is supported by the NPRP 11S-1126-170033 project from the Qatar National Research Fund.
文摘The optical Bloch oscillation(OBO)is an optical-quantum analogy effect that is significant for light field manipulations,such as light beam localization,oscillation and tunneling.As an intra-band oscillation,OBO was important for optical investigations in photonic lattices and atomic vapors over an extended period of time.However,OBO in reconfigurable platforms is still an open topic,even though tunability is highly desired in developing modern photonic techniques.Here we theoretically establish and experimentally demonstrate OBO in an electromagnet-ically induced photonic lattice with a ramping refractive index,established in a coherently-prepared three-level 85 Rb atomic vapor under the electromagnetically induced transparency condition.This is achieved by interfering two coupling beams with Gaussian profiles and launching a probe beam that exhibits OBO within the resulting lattice.The induced reconfigurable photonic lattice possesses a transverse gradient,due to the innate edges of Gaussian beams,and sets a new stage for guiding the flow of light in periodic photonic environments.Our results should motivate better understanding of peculiar physical properties of an intriguing quantum-optical analogy in an atomic setting.
