Phase-coherent multi-tone lasers play a critical role in atomic,molecular,and optical physics.Among them,the Raman opeartion laser for manipulating atomic hyperfine qubits requires gigahertz bandwidth and low phase no...Phase-coherent multi-tone lasers play a critical role in atomic,molecular,and optical physics.Among them,the Raman opeartion laser for manipulating atomic hyperfine qubits requires gigahertz bandwidth and low phase noise to retain long-term coherence.Raman operation lasers generated by directly modulated and frequency-multipled infrared lasers are compact and stable but lack feedback control to actively suppress the phase noise,which limits their performance in practical applications.In this work,we employ a fiber electro-optical modulator driven by a voltage-controlled oscillator(VCO)to modulate a monochromatic laser and employ a second-harmonic generation process to convert it to the visible domain,where the beat note of the Raman operation laser is stabilized by controlling the output frequency of VCO with a digital phase-locked loop(PLL).The low-frequency phase noise is effectively suppressed compared to the scheme without active feedback and it reaches-80 d Bc/Hz@5 k Hz with a 20 k Hz loop bandwidth.Furthermore,this compact and robust scheme effectively reduces the system's complexity and cost,which is promising for extensive application in atomic,molecular,and optical physics.展开更多
The UWA channel is characterized as a time-dispersive rapidly fading channel, which in addition exhibits Doppler instabilities and limited bandwidth. To eliminate inter- symbol interference caused by multipath propaga...The UWA channel is characterized as a time-dispersive rapidly fading channel, which in addition exhibits Doppler instabilities and limited bandwidth. To eliminate inter- symbol interference caused by multipath propagation, spatial diversity equalization is the main technical means. The paper combines the passive phase conjugation and spatial processing to maximize the output array gain. It uses signal-to-noise-plus-interference to evaluate the quality of signals received at different channels. The amplitude of signal is weighted using Sigmoid function. Second order PLL can trace the phase variation caused by channel, so the signal can be accumulated in the same phase. The signals received at different channels need to be normal- ized. It adopts fractional-decision feedback diversity equalizer （FDFDE） and achieves diversity equalization by using different channel weighted coefficients. The simulation and lake trial data processing results show that, the optimized diversity receiving equalization algorithm can im- prove communication system＇s ability in tracking the change of underwater acoustic channel, offset the impact of multipath and noise and improve the performance of communication system. The performance of the communication receiving system is better than that of the equal gain combination. At the same time, the bit error rate （BER） reduces 1.8%.展开更多
The phase diagram of the one-dimensional Bose-Hubbard model describing interacting bosons in optical lattice is investigated with the variational approach. This method can also be generalized to the two-dimensional case.
Electron transport through short, phase-coherent metal-graphene-metal devices occurs via resonant transmission through particle-in-a-box-like states defined by the atomically-sharp metal leads. We study the spectrum o...Electron transport through short, phase-coherent metal-graphene-metal devices occurs via resonant transmission through particle-in-a-box-like states defined by the atomically-sharp metal leads. We study the spectrum of particle-in-a-box states for single- and bi-layer graphene, corresponding to massless and massive two-dimensional （2-D） fermions. The density of states D as a function of particle number n shows the expected relationships D（n） -n1/2 for massless 2-D fermions （electrons in single-layer graphene） and D（n） -constant for massive 2-D fermions （electrons in bi-layer graphene）. The single parameters of the massless and massive dispersion relations are found, namely Fermi velocity vF = 1.1 × 10^6 m/s and effective mass m＊ = 0.032 me, where me, is the electron mass, in excellent agreement with theoretical expectations.展开更多
We investigate phase diffusion of a two-component Bose--Einstein condensates prepared initially in arbitrary coherent spin state ｜θ0,φ0｜. Analytical expression of the phase-diffusion time is presented for θ0～π/...We investigate phase diffusion of a two-component Bose--Einstein condensates prepared initially in arbitrary coherent spin state ｜θ0,φ0｜. Analytical expression of the phase-diffusion time is presented for θ0～π/2 case. In comparison with the symmetrical case （i.e., θ0=π/2）, we find that the diffusion process becomes slow due to the reduced atom number variance.展开更多
合成1种查尔酮衍生物1-（芘-1-基）-3-（苯并噻吩-3-基）丙烯酮（PBTAK）,经IR,1 H NMR,13C NMR和HR-MS对其结构进行表征.采用4f相位相干成像技术测定了它的三阶非线性光学性质并确定了相关参数：脉宽为4nm,激光波长为460nm,非线性吸收...合成1种查尔酮衍生物1-（芘-1-基）-3-（苯并噻吩-3-基）丙烯酮（PBTAK）,经IR,1 H NMR,13C NMR和HR-MS对其结构进行表征.采用4f相位相干成像技术测定了它的三阶非线性光学性质并确定了相关参数：脉宽为4nm,激光波长为460nm,非线性吸收系数β=0.23×10-9 m/W,非线性折射率n2=-0.50×10-16 m2/W,三阶非线性极化率χ（3）=9.37×10-21 C;同时测定了紫外光谱、荧光光谱和DSC曲线.运用密度泛函方法计算了PBTAK的分子轨道能量和极化率,结果表明电子转移能在分子内部进行,显示出良好的非线性光学活性.展开更多
基金supported by the National Key Research and Development Program of China(No.2017YFA0304100)National Natural Science Foundation of China(Nos.11774335,11734015,and 12204455)+1 种基金the Key Research Program of Frontier Sciences,CAS(No.QYZDY-SSWSLH003)Innovation Program for Quantum Science and Technology(Nos.2021ZD0301604 and 2021ZD0301200)。
文摘Phase-coherent multi-tone lasers play a critical role in atomic,molecular,and optical physics.Among them,the Raman opeartion laser for manipulating atomic hyperfine qubits requires gigahertz bandwidth and low phase noise to retain long-term coherence.Raman operation lasers generated by directly modulated and frequency-multipled infrared lasers are compact and stable but lack feedback control to actively suppress the phase noise,which limits their performance in practical applications.In this work,we employ a fiber electro-optical modulator driven by a voltage-controlled oscillator(VCO)to modulate a monochromatic laser and employ a second-harmonic generation process to convert it to the visible domain,where the beat note of the Raman operation laser is stabilized by controlling the output frequency of VCO with a digital phase-locked loop(PLL).The low-frequency phase noise is effectively suppressed compared to the scheme without active feedback and it reaches-80 d Bc/Hz@5 k Hz with a 20 k Hz loop bandwidth.Furthermore,this compact and robust scheme effectively reduces the system's complexity and cost,which is promising for extensive application in atomic,molecular,and optical physics.
基金supported by National Natural Science Foundation of China(61531018)
文摘The UWA channel is characterized as a time-dispersive rapidly fading channel, which in addition exhibits Doppler instabilities and limited bandwidth. To eliminate inter- symbol interference caused by multipath propagation, spatial diversity equalization is the main technical means. The paper combines the passive phase conjugation and spatial processing to maximize the output array gain. It uses signal-to-noise-plus-interference to evaluate the quality of signals received at different channels. The amplitude of signal is weighted using Sigmoid function. Second order PLL can trace the phase variation caused by channel, so the signal can be accumulated in the same phase. The signals received at different channels need to be normal- ized. It adopts fractional-decision feedback diversity equalizer （FDFDE） and achieves diversity equalization by using different channel weighted coefficients. The simulation and lake trial data processing results show that, the optimized diversity receiving equalization algorithm can im- prove communication system＇s ability in tracking the change of underwater acoustic channel, offset the impact of multipath and noise and improve the performance of communication system. The performance of the communication receiving system is better than that of the equal gain combination. At the same time, the bit error rate （BER） reduces 1.8%.
文摘The phase diagram of the one-dimensional Bose-Hubbard model describing interacting bosons in optical lattice is investigated with the variational approach. This method can also be generalized to the two-dimensional case.
文摘Electron transport through short, phase-coherent metal-graphene-metal devices occurs via resonant transmission through particle-in-a-box-like states defined by the atomically-sharp metal leads. We study the spectrum of particle-in-a-box states for single- and bi-layer graphene, corresponding to massless and massive two-dimensional （2-D） fermions. The density of states D as a function of particle number n shows the expected relationships D（n） -n1/2 for massless 2-D fermions （electrons in single-layer graphene） and D（n） -constant for massive 2-D fermions （electrons in bi-layer graphene）. The single parameters of the massless and massive dispersion relations are found, namely Fermi velocity vF = 1.1 × 10^6 m/s and effective mass m＊ = 0.032 me, where me, is the electron mass, in excellent agreement with theoretical expectations.
基金supported by the National Natural Science Foundation of China (Grant No. 10804007)the Special Research Foundation and Development Program (Grant No. 200800041003)Research Funds of Beijing Jiaotong University (Grant No. 2007XM049)
文摘We investigate phase diffusion of a two-component Bose--Einstein condensates prepared initially in arbitrary coherent spin state ｜θ0,φ0｜. Analytical expression of the phase-diffusion time is presented for θ0～π/2 case. In comparison with the symmetrical case （i.e., θ0=π/2）, we find that the diffusion process becomes slow due to the reduced atom number variance.
