Realization of low frequency and controllable bandwidth squeezing based on a four-wave-mixing amplifier in rubidium vapor

We experimentally demonstrate the creation of two correlated beams generated by a nondegenerate four-wave-mixing amplifier at λ=795 nm in hot rubidium vapor. We achieve intensity difference squeezing at frequencies as low as 1.5 kHz which is so far the lowest frequency to observe squeezing in an atomic system. The squeezing spans from 5.5 to 16.5 MHz with a maximum squeezing of -5 dB at 1 MHz. We can control the squeezing bandwidth by changing the pump power. Both low frequency and controllable bandwidth squeezing show great potential in sensitivity detection and precise control of the atom optics measurement.     

基于量子增强型光纤马赫-曾德尔干涉仪的低频信号测量

利用低频光通信波段真空压缩态光场可实现基于光纤的量子精密测量.本文利用简并光学参量振荡器实验制备出1550 nm低频真空压缩态光场.在分析频段10—500 kHz范围内压缩态光场的压缩度均达3 dB.用实验制备的1550 nm真空压缩态光场填补光纤马赫-曾德尔干涉仪的真空通道,实现了量子增强型光纤马赫-曾德尔干涉仪,完成了突破标准量子极限的相位调制频率为500 kHz的低频信号测量.与光纤马赫-曾德尔干涉仪相比,测量信噪比提高了2 dB.     

Experimental evidence for Raman-induced limits to efficient squeezing in optical fibers

We report new experiments on polarization squeezing using ultrashort photonic pulses in a single pass of a birefringent fiber. We measure what is to our knowledge a record squeezing of -6.8+/-0.3 dB in optical fibers, which when corrected for linear losses is -10.4+/-0.8 dB. The measured polarization squeezing as a function of optical pulse energy, which spans a wide range from 3.5-178.8 pJ, shows a very good agreement with the quantum simulations, and for the first time we see the proof experimentally that Raman effects limit and reduce squeezing at high pulse energy.     

用外腔谐振倍频产生明亮绿光振幅压缩态光场

用1080nm激光抽运由α-切割Ⅱ类位相匹配KTP晶体和一个凹面镜组成的半整块驻波倍频腔，腔内的两个亚谐波模共振、谐波模近共振，在1080 nm抽运光功率为50mW时，获得了实测3.1±0.2 dB(～51%)的540nm波长明亮振幅压缩光. 关键词： 外腔谐振倍频 Ⅱ 类位相匹配 明亮振幅压缩光     

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.     

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     

Experimental demonstration of quantum teleportation of broadband squeezing

We demonstrate an unconditional high-fidelity teleporter capable of preserving the broadband entanglement in an optical squeezed state. In particular, we teleport a squeezed state of light and observe -0.8+/-0.2 dB of squeezing in the teleported (output) state. We show that the squeezing criterion translates directly into a sufficient criterion for entanglement of the upper and lower sidebands of the optical field. Thus, this result demonstrates the first unconditional teleportation of broadband entanglement. Our teleporter achieves sufficiently high fidelity to allow the teleportation to be cascaded, enabling, in principle, the construction of deterministic non-Gaussian operations.     

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。     

光通信波段低频压缩态光场的实验制备

本文利用周期极化磷酸氧钛钾晶体构成的半整块结构简并光学参量振荡器实验制备了连续变量光通信波段低频压缩态光场。光学参量振荡器的阈值功率为210 mW。当775nm抽运光场功率为130 mW时,在分析频段50kHz~900kHz范围内获得真空压缩态光场。在200kHz分析频率处,压缩态光场的最大压缩度达5.0dB;在最低分析频率50kHz处,压缩态光场的压缩度为2.0dB。该低频压缩态光场可为基于光纤的量子精密测量提供量子光源。     

Soliton squeezing at the gigahertz rate in a Sagnac loop

We demonstrate what is to our knowledge the first all-fiber squeezing experiment. A balanced Sagnac loop is used, and a record 6.1+/-0.2dB of noise reduction below shot noise has been obtained without stabilization. A gigahertz Er-doped fiber laser and a high-power double-clad Er-Yb amplifier have been developed to suppress guided acoustic-wave Brillouin scattering and to make possible the all-fiber configuration.     

Transition Metal Dichalcogenides (WS_2 and MoS_2) Saturable Absorbers for Mode-Locked Erbium-Doped Fiber Lasers

We demonstrate an ultrafast fiber laser based on transition metal dichalcogenide materials which are tungsten disulfide(WS2) and molybdenum disulfide(MoS_2) as saturable absorber(SA). These materials are fabricated via a simple drop-casting method. By employing WS_2, we obtain a stable harmonic mode-locking at the threshold pump power of 184 mW, and the generated soliton pulse has 3.48 MHz of repetition rate. At the maximum pump power of 250 mW, we also obtain a small value of pulse duration, 2.43 ps with signal-to-noise ratio(SNR) of 57 dB.For MoS_2 SA, the pulse is generated at 105 mW pump power with repetition rate of 1.16 MHz. However, the pulse duration cannot be detected by the autocorrelator device as the pulse duration recorded is 468 ns, with the SNR value of 35 dB.     

Amplitude squeezing by means of quasi-phase-matched second-harmonic generation in a lithium niobate waveguide

We demonstrate that traveling-wave second-harmonic generation produces amplitude-squeezed light at both the fundamental and the harmonic frequencies. Quasi-phase-matched second-harmonic conversion efficiencies approaching 60% were obtained in a 26-mm-long single-mode LiNbO(3) waveguide with pulses from a mode-locked laser at 1.53 microm. The amplitude noise of the transmitted fundamental field was measured to be 0.8 dB below the shot-noise level, and the generated 0.765-microm harmonic light was measured to be amplitude squeezed by 0.35 dB. The conversion-efficiency dependence of the observed squeezing at both wavelengths agrees with theoretical predictions. Waveguide losses appear to degrade the squeezing, but the maximum observed squeezing is currently limited only by the available input power.     

Photon number squeezing of ultrabroadband laser pulses generated by microstructure fibers

To the best of our knowledge, we demonstrate for the first time the generation of photon number squeezing by spectral filtering for ultrabroadband light generated by microstructure fibers at 800 nm. A maximum squeezing of 4.6 dB is observed, corresponding to 10.3 dB after correcting for detection losses. We numerically analyzed the quantum dynamics of ultrashort laser pulse propagation through optical fibers by solving a nonlinear quantum Schr?dinger equation that included Raman scattering, especially for the quantum correlation of photon number fluctuation among frequency modes in broadband pulses.     

Efficient polarization squeezing in optical fibers

We report on a novel and efficient source of polarization squeezing that uses a single pass through an optical fiber. Using the fiber's two orthogonal polarization axes produces two identical squeezed beams. Combining these in a Stokes measurement generates polarization squeezing of up to 5.1 +/- 0.3 dB. Furthermore, this scheme enables us to directly measure, for both polarizations, the noise of any given quadrature.     

Noise squeezing in a nanomechanical Duffing resonator

We study mechanical amplification and noise squeezing in a nonlinear nanomechanical resonator driven by an intense pump near its dynamical bifurcation point, namely, the onset of Duffing bistability. Phase sensitive amplification is achieved by a homodyne detection scheme, where the displacement detector's output, which has a correlated spectrum around the pump frequency, is down-converted by mixing with a local oscillator operating at the pump frequency with an adjustable phase. The down-converted signal at the mixer's output could be either amplified or deamplified, yielding noise squeezing, depending on the local oscillator phase.     

Strong relative intensity squeezing by four-wave mixing in rubidium vapor

We have measured -3.5 dB (-8.1 dB corrected for losses) relative intensity squeezing between probe and conjugate beams generated by stimulated, nondegenerate four-wave mixing in hot rubidium vapor. Unlike early observations of squeezing in atomic vapors based on saturation of a two-level system, our scheme uses a resonant nonlinearity based on ground-state coherences in a three-level system. Since this scheme produces narrowband, squeezed light near an atomic resonance, it is of interest for experiments involving cold atoms or atomic ensembles.     

音频段1.34μm压缩态光场的实验制备

音频段压缩态光场是进行连续变量量子精密测量重要的量子资源.本文利用自制的低噪声连续单频671 nm/1.34μm双波长激光器作为抽运源,抽运基于周期极化磷酸氧钛钾晶体的简并光学参量振荡器,进行了光通信波段1.34μm连续变量音频段真空压缩态光场的实验制备.当简并光学参量振荡器运转于阈值以下参量反放大状态时,抽运光场功率为95 mW,本地振荡光功率为60μW时,在分析频率8—100 k Hz范围内研制出1.34μm真空压缩态光场.在分析频率36 k Hz处,压缩态光场的最大压缩度达5.0 d B;在音频频率8k Hz处,压缩态光场的压缩度达3.0 d B.音频段1.34μm压缩态光场可用于实现基于光纤的量子精密测量.     

利用准相位匹配光学参量振荡器获得可调谐强度差压缩光

利用106μm全固化单频Nd:YVO4激光器抽运由PPLN构建的三共振光学参量振荡器，在光学参量振荡器近简并运转的情况下：信号光和闲置光的波长相差约为200nm，观察到了信号光和闲置光的强度起伏的关联，实测强度差噪声压缩度达04dB.在此基础上，利用温度调谐了信号光和闲置光的波长，在17nm的范围内都观察到信号光和闲置光的强度起伏的关联. 关键词： 准相位匹配 光学参量振荡 强度差噪声压缩     

在热压缩态中测量相位算符的涨落

利用热场动力学的方法计算了热压缩态中测量相位算符的涨落，引入了两种类型的基础量子涨落，一种是与测量相位的两个正交分量相联系，另一种是与一个测量相位分量和光子数相联系。由此，研究了热压缩压中测量相位涨落的两种压缩及其与温度的关系。     

Multi-wavelength Brillouin-Raman ring-cavity fiber laser with 22-GHz spacing

We experimentally demonstrate a multi-wave length Brillouin-Raman fiber laser configured in a ring-cavity resonator. Interactions between stimulated Brillouin scattering and Raman amplification in a dispersion compensating fiber, attributed to the generation of 16 output channels at injected Raman pump unit power of 650 mW and Brillouin pump power of 2.0 mW. The first output channel has a peak power of 14.8 mW. By discriminating the even-order Brillouin Stokes signals from circulating in the resonator, the generated output channels were found to have wavelength spacing of ∼22 GHz. The output channels were also found to have average optical signal-to-noise ratio value of 11.7 dB.