Weak water absorption lines around 1.455 and 1.66 μm by CW-CRDS

The absorption spectra of water vapor near 1.455 and 1.66 μm have been recorded with a typical absorption sensitivity of 5 × 10⁻¹⁰ cm⁻¹ by using CW-cavity ring down spectroscopy. A series of 18 distributed feed-back (DFB) lasers was used as sources and allowed for the coverage of the 5911.0-5922.5, 5926-5941.8, 5957.0-6121.6, and 6745-7015.6 cm⁻¹ spectral regions. These regions extend to lower and higher energies our previous study of the water spectrum in the important 1.5 μm transparency window [P. Macko, D. Romanini, S.N. Mikhailenko, O.V. Naumenko, S. Kassi, A. Jenouvrier, Vl.G. Tyuterev, J. Mol. Spectrosc. 227 (2004) 90-108]. The line parameters were determined with the help of an interactive least squares multi-lines fitting program which uses a Voigt function as line profile. More than 1900 water lines with intensities ranging between 10⁻²⁸ and 5 × 10⁻²⁴ cm/molecule at 296 K were measured, about 690 of them being reported for the first time. The rovibrational assignment was performed on the basis of previously determined energy levels and of the results of the variational global calculations [H. Partridge, D.W. Schwenke, J. Chem. Phys. 106 (1997) 4618-4639]. The assignment results were validated by using the Ritz combination principle together with previously reported water transitions. Several new energy levels were determined for the H₂¹⁶O, H₂¹⁷O, and HD¹⁶O isotopologues. The retrieved line lists of the H₂¹⁶O, H₂¹⁷O, H₂¹⁸O, and HD¹⁶O isotopologues are compared with the available calculated and experimental (FTS) databases for water.     

延迟光反馈VCSEL的混沌动力学特性

根据延迟光反馈垂直腔面发射半导体激光器动力学模型,数值模拟了激光器的混沌动力学特性,分析了外腔长度和光反馈强度对激光器混沌动力学特性的影响.结果表明:外腔较短的激光器,经过混沌区后仍会回到锁频状态|外腔较长的激光器,经过混沌区后不是进入锁频状态而是回到周期1.取定激光器外腔长度为3.0 cm,使反馈强度由小增大,得到激光器由倍周期分岔进入混沌的过程,并在混沌区中出现周期12窗口.本文对混沌保密通信的实际应用具有一定的理论参考价值.     

腔QED中利用超导量子干涉仪实现Toffoli门

基于腔量子电动力学技术,提出了利用三能级超导量子干涉仪实现Toffoli门的理论方案.利用超导量子干涉仪与腔场发生耦合,以及与外加经典脉冲发生共振跃迁来实现量子态的演化控制.该方案可以拓展到N比特Toffoli门的实现.最后,讨论了逻辑门的实验可行性,四比特Toffoli门的作用时间约为30 nm,它远小于腔衰减时间和较高能级的能量驰豫时间,从而足以实现量子态的操控.并且随着比特数的增多,Toffoli门作用时间的增幅较慢.     

光学元件失调对光腔衰荡高反射率测量影响的理论分析

在利用光反馈光腔衰荡技术测量大口径光学元件反射率及其均匀性分布时,需要对光学元件进行二维扫描测量,而在扫描过程中光学元件的倾斜失调将对测量结果造成影响.本文根据失调谐振腔光束传输增广矩阵,通过数值运算模拟了在对称共焦腔和一般稳定腔情况下,光反馈衰荡腔结构中由样品倾斜失调引起的输出腔镜上光斑中心位置变化以及对反射率测量的影响.仿真结果表明:对称共焦腔情况下,输出腔镜上奇数次光斑无漂移,偶数次光斑漂移量为固定值|在一般稳定腔情况下,输出腔镜上奇偶数次光斑均往复振荡漂移.分析表明,该系统对样品失调角度的敏感程度与样品在腔内的位置以及腔长有关,通过改变样品在腔内位置,选择适当腔长以及包络拟合法可以减小样品失调对测量结果的影响.     

增光子二模纠缠相干态的纠缠特性及其通过腔量子电动力学的制备

分析了增光子二模纠缠相干态的纠缠特性,得到共生纠缠度的解析表示式.结果表明:增光子二模纠缠相干态的共生纠缠度与叠加态的相位有非常灵敏的关系.提出了一种制备增光子相干态和增光子二模纠缠相干态的方法,其制备过程为首先把增光子相干态转化为相干态与真空态一种特殊的叠加态(叠加系数与相干态振幅有关),再通过位于高Q腔内的原子与经典激光场的相互作用,从而实现增光子相干态的制备.通过一个飞行原子先后与两个光腔中光场相互作用可以实现增光子二模纠缠相干态的制备.     

Design of high-Q cavities in 2D photonic crystals air holes filled with polymer

We design novel photonic crystal heterostructure, substituting the air in the holes with materials of refractive index higher than n = 1. This can be achieved by infiltrating the photonic crystal (PC) with polymer. We theoretically investigate the L₂ cavity with two missing holes in the center, where the six holes surrounding the cavity are locally filled with polymer. We show that cavity modes can be differently tuned depending on the size and the position of the first hole adjacent to the cavity. A photonic microcavity with a high Q factor of 5.5 × 10⁶ and a modal volume V of 0.1919 is demonstrated. We demonstrate that the calculated Q factor for the designed cavity increases by a factor of 22 relative to that for a cavity without displaced and reduced air holes, while the modal volume remains almost constant.     

An ultra compact photonic crystal wavelength division demultiplexer using resonance cavities in a modified Y-branch structure

An ultra small size 4-channel wavelength division demultiplexer based on 2D photonic crystal modified Y-Branch, suitable for integration, is proposed in this paper. The output wavelengths of designed structure can be tuned for communication applications (around 1550 nm) by choosing suitable defect parameters in the corner of each resonance cavity and output waveguides. The cross section of the structure is 313.28 μm² (17.8 μm × 17.6 μm) and desirable for integration based on popular planar technology. The bandwidth of each channel is near to 1 nm and the channel spacing is approximately 3.5 nm and wavelengths of demultiplexer channels are 1548.8 nm, 1551.9 nm, 1555.4 nm and 1559.3 nm respectively. Also, the crosstalk is between −33.1855 dB and −10.4947 dB. Furthermore, the mean values of the crosstalk and quality factor are −22.54 dB and 1496.7 respectively.     

Effects of vacuum fluctuation suppression on atomic decay rates

The use of atomic decay rates as a probe of sub-vacuum phenomena will be studied. Because electromagnetic vacuum fluctuations are essential for radiative decay of excited atomic states, decay rates can serve as a measure of the suppression of vacuum fluctuations in non-classical states, such as squeezed vacua. In such states, the renormalized expectation value of the square of the electric field or the energy density can be periodically negative, representing suppression of vacuum fluctuations. We explore the extent to which atomic decays can be used to measure the mean squared electric field or energy density. We consider a scheme in which atoms in an excited state transit a closed cavity whose lowest mode contains photons in a non-classical state. A crucial feature of our analysis is that we do not employ the rotating wave approximation. The change in the decay probability of the atom in the cavity due to the non-classical state can, under certain circumstances, serve as a measure of the mean squared electric field or energy density in the cavity. We make some estimates of the magnitude of this effect, which indicate that an experimental test might be possible, although very challenging.     

Fast quantum search algorithm for databases of arbitrary size and its implementation in a cavity QED system

We propose a method for implementing the Grover search algorithm directly in a database containing any number of items based on multi-level systems. Compared with the searching procedure in the database with qubits encoding, our modified algorithm needs fewer iteration steps to find the marked item and uses the carriers of the information more economically. Furthermore, we illustrate how to realize our idea in cavity QED using Zeeman?s level structure of atoms. And the numerical simulation under the influence of the cavity and atom decays shows that the scheme could be achieved efficiently within current state-of-the-art technology.     

光子晶体滤波特性分析

采用时域有限差分(FDTD)方法,研究光在含点缺陷(即微腔)和线缺陷(即波导)的光子晶体中的传输特性.计算结果表明,处于光子晶体禁带的光能被局域在光子晶体波导中传输.而具有特定本征共振频率的光子晶体微腔可将在其附近波导中传播的相应频率成份的光下载到微腔中,不同结构的腔可以“下载”不同频率成份的波.以上计算结果,可用于光子晶体上/下载滤波器的设计.