Squeezing via coupling of Bose--Einstein condensates in a double-well potential with a cavity light field

Squeezing via the interaction between the cavity light field and the Bose Einstein Condensate （BEC） in a doublewell potential is considered within the context of the two-mode approximation. For the cavity light field initially in a coherent state, it is shown that by choosing appropriate parameters, quadrature squeezing of the cavity light field can be achieved and it exhibits periodic oscillation. We also study the case in which BEC is tuned to resonance by periodically modulating the trapping potentiaL and the quadrature squeezing of the cavity field exhibits periodic collapse and revival effect. Both analytic and numerical calculations are performed, and they are found to be in good agreement with each other. The result shows that the quantum statistical properties of the cavity light field can be manipulated by its coupling with the condensates in the double-well potential. On the other hand, dynamical properties of the condensates in the double-well potential will be reflected by the quadrature squeezing of the light field.     

Einstein——Podolsky——Rosen entanglement in time-dependent periodic pumping non-degenerate optical parametric amplifier

The solution of the time-dependent periodic pumping non-degenerate optical parametric amplifier (NOPA) is derived when the pump depletion is considered both above and below thresholds. Based on this solution, the quantum fluctuation calculated shows that a high entanglement and a good squeezing degree of the parametric light beams are achieved near and above thresholds. We adopt two kinds of pump fields: (i) a continuously modulated pump with a sinusoidal envelope; (ii) a sequence of laser pulses with Gaussian envelopes. We analyse the time evolution of continuous variable entanglement by analytical and numerical calculations, and show that the periodic driven pumping also improves the degree of entanglement. The squeezing and Einstein-Podolsky-Rosen (EPR) entanglement by using the two pumping driven functions are investigated from below to above the threshold regions, the tendencies are nearly the same, and the Gaussian driven function is superior to that of the sine driven function, when the maximum squeezing and the minimum variance of quantum fluctuation are considered. In the meantime, the generalization of frequency degenerate OPA to frequency non-degenerated OPA problem is investigated.     

Noise transfer of pump field noise with analysis frequency in a broadband parametric downconversion process

Our previous work had proved pump field noise coupling in the seed field injected optical parametric amplifier(OPA) at a certain analysis frequency. Inspired by this noise coupling mechanism, the frequency dependent squeezing factor due to excess pump noise was experimentally demonstrated. Apart from a reduced squeezing level with an increased noise, the results also prove that a broadband squeezing noise spectrum is not frequency dependent on the amplitude modulated pump field, but limited by the bandwidth of the amplitude modulator and OPA resonator, and the effective measurement is carried out in the frequency range of 2–10 MHz. It provides a guidance to design a broader-bandwidth, higher-level bright squeezed light.     

Collapse–revival of squeezing of two atoms in dissipative cavities

Based on the time-convolutionless master-equation approach, we investigate the squeezing dynamics of two atoms in dissipative cavities. We find that the atomic squeezing is related to initial atomic states, atom–cavity couplings, nonMarkovian effects and resonant frequencies of an atom and its cavity. The results show that a collapse–revival phenomenon will occur in the atomic squeezing and this process is accompanied by the buildup and decay of entanglement between two atoms. Enhancing the atom–cavity coupling can increase the frequency of the collapse–revival of the atomic squeezing.The stronger the non-Markovian effect is, the more obvious the collapse–revival phenomenon is. In particular, if the atom–cavity coupling or the non-Markovian effect is very strong, the atomic squeezing will tend to a stably periodic oscillation in a long time. The oscillatory frequency of the atomic squeezing is dependent on the resonant frequency of the atom and its cavity.     

Tunable ponderomotive squeezing in an optomechanical system with two coupled resonators

We investigate properties of the ponderomotive squeezing in an optomechanical system with two coupled resonators,where the tunable two-mode squeezing spectrum can be observed from the output field.It is realized that the squeezing orientation can be controlled by the detuning between the left cavity and pump laser.Especially,both cavity decay and environment temperature play a positive role in generating better pondermotive squeezing light.Strong squeezing spectra with a wide squeezing frequency range can be obtained by appropriate choice of parameters present in our optomechanical system.     

Sum and two—atom dipole squeezing in a system of a two—mode vacuum field interacting with two coupled atoms

We discuss the effects of the initial atomic coherent factors (including the phase and the distribution parameter) and the dipole-dipole interaction on the sum and two-atom dipole squeezing in the system.The results show that the maximum squeezing in both cases is determined by the phase and the distribution parameter,and the duration of squeezing becomes longer by strengthening the dipole-dipole interaction.In addition,the comparison of the two types of squeezing shows that one type of squeezing is obtained at the expense of increased fluctuations in the other squeezing function.     

Numerical analysis of polarization character in Yb~(3+)-doped fiber amplifiers

Polarization-dependent gain (PDG) and state of polarization (SOP) of the output signal light in Yb3+-doped fiber amplifiers are studied by numerically stimulation, which showed that PDG of output signal light is not only changed with the input pump power and signal power, input polarization of pump and signal light, but also changed with the doping concentration, the cross-section anisotropy, the fiber length, the phase difference of the fiber, and so on. Moreover, SOP of the output signal light is studied. It is found that the polarization of output signal light is relative not only to the phase difference of the fiber, polarization of pump and signal light as the non-doped fiber, but also to PDG of output signal light, the cross-section anisotropy, the doping concentration, and so on, which is different to the non-doped fiber.     

Cavity-Induced Enhancement of Squeezing in Resonance Fluorescence of a V-Type Three-Level Atom

The quadrature squeezing spectra in the resonance fluorescence of a V-type three-level atom driven by a coherent field and coupled to a single-mode cavity is investigated. For weak excitation, the fluorescence field exhibit squeezing in the out-of-phase quadrature. The coupling between the atom and the cavity mode can greatly enhance the squeezing centred at the laser frequency. More importantly, for strong excitation, under the effect of the cavity-atom coupling, the in-phase quadrature of fluorescence can exhibit two-mode squeezing at the two inner sideband frequencies. By working in the dressed-state representation and hiring secular approximation, we give an analytical explanation for the effect. The result shows, under appropriate conditions, the squeezing can be greatly enhanced by appropriately tuning the cavity resonant frequency.     

Efficient Generation of Squeezed Light Based on MgO-Doped Periodically Poled LiNbO3

We demonstrate a high-efficiency green light conversion from an external cavity second harmonic generation with a MgO-doped periodically poled LiNb03 crystal. The frequency doubler can reach a conversion efficiency of 64% with a fundamental power of 26mW. Meanwhile, the generated green light is quadrature-amplitude squeezed and 1.2 dB green light squeezing is experimentally measured. The squeezing at different pump levels is also investigated and is in good agreement with the theoretical prediction.     

Measurement of intensity difference squeezing via non-degenerate four-wave mixing process in an atomic vapor

We report the measurement of the intensity difference squeezing via the non-degenerate four-wave mixing process in a rubidium atomic vapor medium. Two pairs of balanced detection systems are employed to measure the probe and the conjugate beams, respectively. It is convenient to get the quantum shot noise limit, the squeezed and the amplified noise power spectra. We also investigate the influence of the input extra quadrature amplitude noise of the probe beam. The influence of the extra noise can be minimized and the squeezing can be optimized under the proper parameter condition. We measure the -3.7-dB intensity difference squeezing when the probe beam has a 3-dB extra quadrature amplitude noise. This result is slightly smaller than -4.1 dB when the ideal coherent light （no extra noise） for the probe beam is used.     

Influence of random deviation of domain length in quasi-phase-matched crystals on degenerate optical parametric amplification

During the fabrication of quasi-phase-matched (QPM) devices, errors of periodic structure are usually inevitable. The errors result in the deviation of the actual periodic domain length from the theoretical value. In this paper we numerically analyze the influence of the errors on the degenerate optical parametric amplifier consisting of QPM devices. It is shown that in this case the gains of signal photon number and normalized photon number variance are decreased with respect to those of an ideal QPM device. However, there are no extra noises to be introduced, the output signal-noise-ratio is equal to the input signal-noise-ratio if the small linear absorption in QPM devices is ignored. It has been also proved that the noise figure of the noiseless amplifier does not vary with the pump power and the propagation length of the signal light in the QPM crystal.     

三共振准相位匹配光学参量振荡器反射抽运场的正交位相压缩

利用全固化单频Nd∶YVO₄激光器抽运由periodically poled lithium niobate(PPLN)准相位匹配晶体组成的光学参量振荡器,通过调节晶体的温度,在信号模与闲置模近简并的情况下,完成了抽运场与两个亚谐波模在腔内同时共振,实现了光学参量振荡器的极低阈值运转(阈值为1.2mW);当抽运功率为阈值抽运功率的2.8倍时,观察到反射抽运光的正交位相压缩,压缩度达1.1dB.数值计算与实验结果一致     

V型三能级原子与非经典光场作用中光场特性的变化

研究了V型三能级原子BEC与双模压缩光场相互作用系统中,忽略原子间相互作用和考虑原子间相互作用时光场的正交压缩和光子数压缩。结果表明,光场的正交压缩依赖于压缩参数,而光子数压缩与压缩参数、光场信号强度有关,在一定条件下,两种压缩可同时存在。原子间相互作用影响两种压缩的涨落随时间变化的周期,以及正交分量涨落随时间变化的幅度,而对光子数压缩涨落随时间变化的幅度几乎无影响。     

利用周期性极化KTP外腔谐振倍频过程实现明亮振幅压缩光

利用自制的单频连续Nd:YVO4激光器输出的1064 nm激光作为抽运源,通过周期性极化KTP晶体外腔倍频过程实现了倍频绿光的正交振幅压缩,并研究了绿光压缩度对抽运光功率的依赖关系,当抽运光功率为59 mW时,实验中观察到压缩度为0.6 dB(考虑到探测效率,实际压缩度为1.1 dB)的明亮绿光振幅压缩光,实验结果与理论预测基本一致。     

Efficiency pedestal in quasi-phase-matching devices with random duty-cycle errors

It is shown that random duty-cycle errors in quasi-phase-matching (QPM) nonlinear optical devices enhance the efficiency of processes far from the QPM peak. An analytical theory is shown to agree well with numerical solutions of second-harmonic generation (SHG) in disordered QPM gratings. The measured efficiency of 1550?nm band SHG in a periodically poled lithium niobate (PPLN) waveguide away from the QPM peak agrees with observations of domain disorder in a PPLN wafer by Zygo interferometry. If suppression of parasitic nonlinear interactions is important in a specific application of QPM devices, control of random duty-cycle errors is critical.     

对应于铯原子D1线连续可调谐正交压缩态光场的制备

铯原子D₁线的非经典光由于其波长接近于量子点的独特优势,在固态量子信息网络的发展中有着重要的应用前景.在之前的工作中,利用两镜连续简并光学参量振荡器中的参量下转换过程,制备出2.8 d B正交压缩真空态光场.然而,所产生光场的压缩度较低,对于对压缩光具有实用意义的可调谐性能也未做进一步探究.理论分析表明,光学参量振荡器后腔镜对信号光透射率的增加及内腔损耗的减小可以提高压缩度.因此,本文在该研究基础上,通过使用高光洁度腔镜及优化腔镜镀膜参数等方式对光学参量振荡器进行改良,降低了光学参量腔阈值,获得压缩度为3.3 d B的单模正交压缩真空光.当光学参量腔运转为参量反放大状态时,在系统稳定运行的情况下,制备的明亮压缩态光场能够连续调谐80 MHz,为其在量子信息网络中的应用奠定了良好的基础.     

双模场与V型三能级原子玻色-爱因斯坦凝聚体相互作用系统的光场压缩效应

研究了V型三能级原子玻色-爱因斯坦凝聚体与双模压缩相干态光场相互作用系统中的光场压缩的特性。数值计算结果表明：光场的正交分量呈现周期性压缩,其周期与原子间相互作用密切相关,而最大压缩量与持续时间与初始光场的压缩因子有关。     

The Spectrum of Squeezing in Degenerate Four-Wave Mixing

We analyze a simple model for degenerate four wave mixing, introduced by Savage and Walls. In the resonant case, the system exhibits a phase instability when the pump intensity is increased well beyond the threshold for generation of the signal mode. Still in the resonant configuration, we calculate the amplitude and phase squeezing spectra both for the signal and the pump mode. In the signal (pump) mode, the squeezing becomes especially large when the signal (pump) mode is much more damped than the pump (signal) mode. The signal field can exhibit both phase and amplitude squeezing, in distinct domains of the parameter space. On the other hand, the pump field can show squeezing only in the amplitude quadrature component. In general, the model exhibits sizable squeezing over very extended regions of the parameter space.     

三能级原子系统中原子偶极压缩和光场压缩间的关联

通过考察三能级原子与单模和双模场相互作用系统中原子偶极压缩和光场压缩随时间的演化规律, 研究了原子偶极压缩与光场压缩之间的关系, 讨论了原子偶极压缩与光场压缩之间相互转换的特征, 并给出了初始处于偶极压缩状态的原子辐射压缩光的条件。