We develop a variational theory for a dipolar condensate in an elongated(cigar shaped)confinement potential. Our formulation provides an effective one-dimensional extended meanfield theory for the ground state and its...We develop a variational theory for a dipolar condensate in an elongated(cigar shaped)confinement potential. Our formulation provides an effective one-dimensional extended meanfield theory for the ground state and its collective excitations. We apply our theory to investigate the properties of rotons in the system comparing the variational treatment to a full numerical solution. We consider the effect of quantum fluctuations on the scattering length at which the roton excitation softens to zero energy.展开更多
We study analytically and numerically the nonlinear collective dynamics of quasi-one-dimensional spin-orbit coupled spin-1 Bose-Einstein condensates trapped in harmonic potential.The ground state of the system is dete...We study analytically and numerically the nonlinear collective dynamics of quasi-one-dimensional spin-orbit coupled spin-1 Bose-Einstein condensates trapped in harmonic potential.The ground state of the system is determined by minimizing the Lagrange density,and the coupled equations of motions for the center-of-mass coordinate of the condensate and its width are derived.Then,two low energy excitation modes in breathing dynamics and dipole dynamics are obtained analytically,and the mechanism of exciting the anharmonic collective dynamics is revealed explicitly.The coupling among spin-orbit coupling,Raman coupling and spin-dependent interaction results in multiple external collective modes,which leads to the anharmonic collective dynamics.The cooperative effect of spin momentum locking and spin-dependent interaction results in coupling of dipolar and breathing dynamics,which strongly depends on spin-dependent interaction and behaves distinct characters in different phases.Interestingly,in the absence of spin-dependent interaction,the breathing dynamics is decoupled from spin dynamics and the breathing dynamics is harmonic.Our results provide theoretical evidence for deep understanding of the ground sate phase transition and the nonlinear collective dynamics of the system.展开更多
Temperature,as a measure of thermal motion,is a significant parameter characterizing a cold atomic ensemble optical quantum memory.In a cold gas,storage lifetime strongly depends on its temperature and is associated w...Temperature,as a measure of thermal motion,is a significant parameter characterizing a cold atomic ensemble optical quantum memory.In a cold gas,storage lifetime strongly depends on its temperature and is associated with the spin wave decoherence.Here we experimentally demonstrate a new spin wave thermometry method relying on this direct dependence.The short-wavelength spin waves resulting from the counter-propagating configuration of the control and the probe laser beams make this thermometry highly suitable for probing in situ the atomic motion in elongated clouds as the ones used in quantum memories.Our technique is realized with comparable precision for memories that rely on electromagnetically induced transparency as well as far-detuned Raman storage.展开更多
We study the Bose–Einstein condensation of parallel light in a two-dimensional nonlinear optical cavity,where the massive photons are converted into photon molecules(p-molecules).We extend the classical-field method ...We study the Bose–Einstein condensation of parallel light in a two-dimensional nonlinear optical cavity,where the massive photons are converted into photon molecules(p-molecules).We extend the classical-field method to provide a description of the two-component system,and we also derive a coupled density equation which can be used to describe the conversion relation between photons and p-molecules.Furthermore,we obtain the chemical potential of the system,and we also find that the system can transform from the mixed photon and p-molecule condensate phase into a pure p-molecule condensate phase.Additionally,we investigate the collective excitation of the system.We also discuss the problem how the spontaneous decay of an atom is influenced by both the phase transition and collective excitation of the coupling system.展开更多
A very long lifetime exciton emission with non-single exponential decay characteristics has been reported for single InA-s/GaAs quantum dot(QD)samples,in which there exists a long-lived metastable state in the wetting...A very long lifetime exciton emission with non-single exponential decay characteristics has been reported for single InA-s/GaAs quantum dot(QD)samples,in which there exists a long-lived metastable state in the wetting layer(WL)through radiative field coupling between the exciton emissions in the WL and the dipole field of metal islands.In this article we have proposed a new three-level model to simulate the exciton emission decay curve.In this model,assuming that the excitons in a metastable state will diffuse and be trapped by QDs,and then emit fluorescence in QDs,a stretchedlike exponential decay formula is derived as I(t)=At^(β−1)e^(−(rt)^(β)),which can describe well the long lifetime decay curve with an analytical expression of average lifetime(τ)=1/rГ(1/β+1),where G is the Gamma function.Furthermore,based on the proposed three-level model,an expression of the second-order auto-correlation function g^(2)(t)which can fit the measured g^(2)(t)curve well,is also obtained.展开更多
Schrödinger cat states,consisting of superpositions of macroscopically distinct states,provide key resources for a large number of emerging quantum technologies in quantum information processing.Here we propose h...Schrödinger cat states,consisting of superpositions of macroscopically distinct states,provide key resources for a large number of emerging quantum technologies in quantum information processing.Here we propose how to generate and manipulate mechanical and optical Schrödinger cat states with distinguishable superposition components by exploiting the unique properties of cavity optomechanical systems based on Bose-Einstein condensate.Specifically,we show that in comparison with its solid-state counterparts,almost a 3 order of magnitude enhancement in the size of the mechanical Schrödinger cat state could be achieved,characterizing a much smaller overlap between its two superposed coherent-state components.By exploiting this generated cat state,we further show how to engineer the quadrature squeezing of the mechanical mode.Besides,we also provide an efficient method to create multicomponent optical Schrödinger cat states in our proposed scheme.Our work opens up a new way to achieve nonclassical states of massive objects,facilitating the development of fault-tolerant quantum processors and sensors.展开更多
We develop a numerical method for approximating the surface modes of sphere-like nanoparticles in the quasi-static limit,based on an expansion of(the angular part of)the potentials into spherical harmonics.Comparisons...We develop a numerical method for approximating the surface modes of sphere-like nanoparticles in the quasi-static limit,based on an expansion of(the angular part of)the potentials into spherical harmonics.Comparisons of the results obtained in this manner with exact solutions and with a perturbation ansatz prove that the scheme is accurate if the shape deviations from a sphere are not too large.The method allows fast calculations for large numbers of particles,and thus to obtain statistics for nanoparticles with random shape fluctuations.As an application we present some statistics for the distribution of resonances,polariziabilities,and dipole axes for particles with random perturbations.展开更多
文摘We develop a variational theory for a dipolar condensate in an elongated(cigar shaped)confinement potential. Our formulation provides an effective one-dimensional extended meanfield theory for the ground state and its collective excitations. We apply our theory to investigate the properties of rotons in the system comparing the variational treatment to a full numerical solution. We consider the effect of quantum fluctuations on the scattering length at which the roton excitation softens to zero energy.
基金supported by the National Natural Science Foundation of China(Grant Nos.12164042,12264045,11764039,11475027,11865014,12104374,and 11847304)the Natural Science Foundation of Gansu Province(Grant Nos.17JR5RA076 and 20JR5RA526)+2 种基金the Scientific Research Project of Gansu Higher Education(Grant No.2016A-005)the Innovation Capability Enhancement Project of Gansu Higher Education(Grant Nos.2020A-146 and 2019A-014)the Creation of Science and Technology of Northwest Normal University(Grant No.NWNU-LKQN-18-33)。
文摘We study analytically and numerically the nonlinear collective dynamics of quasi-one-dimensional spin-orbit coupled spin-1 Bose-Einstein condensates trapped in harmonic potential.The ground state of the system is determined by minimizing the Lagrange density,and the coupled equations of motions for the center-of-mass coordinate of the condensate and its width are derived.Then,two low energy excitation modes in breathing dynamics and dipole dynamics are obtained analytically,and the mechanism of exciting the anharmonic collective dynamics is revealed explicitly.The coupling among spin-orbit coupling,Raman coupling and spin-dependent interaction results in multiple external collective modes,which leads to the anharmonic collective dynamics.The cooperative effect of spin momentum locking and spin-dependent interaction results in coupling of dipolar and breathing dynamics,which strongly depends on spin-dependent interaction and behaves distinct characters in different phases.Interestingly,in the absence of spin-dependent interaction,the breathing dynamics is decoupled from spin dynamics and the breathing dynamics is harmonic.Our results provide theoretical evidence for deep understanding of the ground sate phase transition and the nonlinear collective dynamics of the system.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.12074171,12074168,92265109,and 12204227)the Key Laboratory Fund from Guangdong Province,China(Grant No.2019B121203002)the Natural Science Foundation of Guangdong Province,China(Grant Nos.2022B1515020096 and 2019ZT08X324).
文摘Temperature,as a measure of thermal motion,is a significant parameter characterizing a cold atomic ensemble optical quantum memory.In a cold gas,storage lifetime strongly depends on its temperature and is associated with the spin wave decoherence.Here we experimentally demonstrate a new spin wave thermometry method relying on this direct dependence.The short-wavelength spin waves resulting from the counter-propagating configuration of the control and the probe laser beams make this thermometry highly suitable for probing in situ the atomic motion in elongated clouds as the ones used in quantum memories.Our technique is realized with comparable precision for memories that rely on electromagnetically induced transparency as well as far-detuned Raman storage.
基金Project supported by the Graduate Science and Technology Innovation Project of Shanxi Normal University(Grant No.01053011)the Chinese Academy of Sciences(CAS)Large-Scale Scientific Facility Program(Grant No.1G2017IHEPKFYJO1).
文摘We study the Bose–Einstein condensation of parallel light in a two-dimensional nonlinear optical cavity,where the massive photons are converted into photon molecules(p-molecules).We extend the classical-field method to provide a description of the two-component system,and we also derive a coupled density equation which can be used to describe the conversion relation between photons and p-molecules.Furthermore,we obtain the chemical potential of the system,and we also find that the system can transform from the mixed photon and p-molecule condensate phase into a pure p-molecule condensate phase.Additionally,we investigate the collective excitation of the system.We also discuss the problem how the spontaneous decay of an atom is influenced by both the phase transition and collective excitation of the coupling system.
基金Project supported by the National Key Research and Development Program of China(Grant No.2016YFA0301202)the National Natural Science Foundation of China(Grant Nos.61827823 and 11974342).
文摘A very long lifetime exciton emission with non-single exponential decay characteristics has been reported for single InA-s/GaAs quantum dot(QD)samples,in which there exists a long-lived metastable state in the wetting layer(WL)through radiative field coupling between the exciton emissions in the WL and the dipole field of metal islands.In this article we have proposed a new three-level model to simulate the exciton emission decay curve.In this model,assuming that the excitons in a metastable state will diffuse and be trapped by QDs,and then emit fluorescence in QDs,a stretchedlike exponential decay formula is derived as I(t)=At^(β−1)e^(−(rt)^(β)),which can describe well the long lifetime decay curve with an analytical expression of average lifetime(τ)=1/rГ(1/β+1),where G is the Gamma function.Furthermore,based on the proposed three-level model,an expression of the second-order auto-correlation function g^(2)(t)which can fit the measured g^(2)(t)curve well,is also obtained.
基金supported by the National Natural Science Foundation of China(NSFC)(11935006 and 11774086)the Science and Technology Innovation Program of Hunan Province(2020RC4047)+6 种基金L.-M.K.was supported by the NSFC(1217050862,11935006 and 11775075)X.-W.X.was supported by the NSFC(12064010)Natural Science Foundation of Hunan Province of China(2021JJ20036)Y.-F.J.was supported by the NSFC(12147156)the China Postdoctoral Science Foundation(2021M701176)the Science and Technology Innovation Program of Hunan Province(2021RC2078)B.J.L.was supported by Postgraduate Scientific Research Innovation Project of Hunan Province(CX20210471).
文摘Schrödinger cat states,consisting of superpositions of macroscopically distinct states,provide key resources for a large number of emerging quantum technologies in quantum information processing.Here we propose how to generate and manipulate mechanical and optical Schrödinger cat states with distinguishable superposition components by exploiting the unique properties of cavity optomechanical systems based on Bose-Einstein condensate.Specifically,we show that in comparison with its solid-state counterparts,almost a 3 order of magnitude enhancement in the size of the mechanical Schrödinger cat state could be achieved,characterizing a much smaller overlap between its two superposed coherent-state components.By exploiting this generated cat state,we further show how to engineer the quadrature squeezing of the mechanical mode.Besides,we also provide an efficient method to create multicomponent optical Schrödinger cat states in our proposed scheme.Our work opens up a new way to achieve nonclassical states of massive objects,facilitating the development of fault-tolerant quantum processors and sensors.
基金supported in part by the DFG through Grant No.KI 438/8-1.
文摘We develop a numerical method for approximating the surface modes of sphere-like nanoparticles in the quasi-static limit,based on an expansion of(the angular part of)the potentials into spherical harmonics.Comparisons of the results obtained in this manner with exact solutions and with a perturbation ansatz prove that the scheme is accurate if the shape deviations from a sphere are not too large.The method allows fast calculations for large numbers of particles,and thus to obtain statistics for nanoparticles with random shape fluctuations.As an application we present some statistics for the distribution of resonances,polariziabilities,and dipole axes for particles with random perturbations.