【作者】 翟畅；

【导师】 郭光灿； 史保森；

【作者基本信息】 中国科学技术大学 ， 光学， 2010， 博士

【摘要】 自发参量下转换获得的光子具有高度的相关性,是一种重要的非经典光场。在非线性晶体中通过自发参量下转换产生光子对,是一种最为成熟的产生纠缠光子对以及获得单光子的方法,在光通讯、量子光学和量子信息领域有着极为重要的作用。特别是在量子通讯领域用来携带信息,被称为飞行比特,是量子通信网络重要的一环。因此得到高亮度的光子对,提高参量下转换的效率就有十分重要的研究价值。在另一方面,构筑量子通信网络需要对光子所携带的信息进行存储,实现这个存储功能的部件称为量子中继,目前原子系综被认为非常适合作为量子中继器,但是由于原子的自然线宽仅为MHz量级,而携带信息的参量下转换光子带宽约为THz量级,这样悬殊的差别使得这种光子无法有效的同原子相互作用,即无法实现量子信息的传递,因此研究压窄光子的线宽也具有非常重要的意义。本文的主要内容归纳如下：1,基于非线性周期极化晶体PPKTP的倍频实验研究。我们分别进行了连续激光的腔内倍频实验和超短脉冲的倍频实验。连续激光的腔内倍频实验中,我们选用780nm的外腔式半导体激光器倍频获得390nm的紫外光源,得到的紫外光输出功率为8.8mW,对应的转化效率为12%,实验得到的390nm的紫外光将作为进一步实验(参量下转换实验)的泵浦光。超短脉冲的倍频实验中,使用800nm的飞秒激光,进行了Ⅱ型准相位匹配实验,归一化转换效率为0.36%W-1cm-1。2,通过PPKTP的自发参量下转换过程制备光子对。我们分别利用半导体激光和腔内倍频产生的激光作为泵浦光在PPKTP中产生光子对,当泵浦源为半导体激光时,泵浦光功率为3.58mW,探测到的纯复合计数为7400／s,对应的光子对产生率为0.73MHz／mW。当使用腔内倍频产生的激光作为泵浦光时,泵浦光功率为0.11mW,在半高全宽为40nm的全带宽范围内,得到的复合计数约为340k／s,对应的光子对产生率为94MHz／mW,使用3nm的干涉滤波片后,纯复合计数为11.5k／s,可知光子对产生率为4.3 MHz／mW／nm。3,多纵模光子相干长度的实验测量和理论分析。我们通过实验测量了运行在远低于阈值的情况下,OPO腔中产生的自发参量下转换光子的一阶相干长度。实验中OPO腔的带宽为7.8MHz,得到的单光子的相干长度为90μm,对应的带宽为0.47nm,我们同时也对此过程进行理论分析计算,计算得到的单光子的相干长度110μm,实验结果和理论结果比较符合。4,基于PPKTP波导产生多通道光子对。我们提出了一种利用周期极化磷酸氧钛钾波导,通过自发参量下转换过程来获得多通道光子对的方案,这个方案旨在能够同时提供多组光子对给量子网络的多对通讯者,从而有效的建立并简化量子网络。更多还原

【Abstract】 Spontaneous parametric downconversion photons have good quantum correlation as one important type of non classical field. So far, the most mature way of obtaining the entangled photon pairs is the spontaneous parametric downconversion (SPDC) method in a nonlinear crystal. SPDC photon is widely used in quantum optics and quantum information field, especially in quantum net work used as a flying bit to carry information. In another point, quantum memory (quantum reperter) is also a key component to bulid up a quantum network. The atomic system is regard as a good candidate for quantum reperter. The typical natural linewidth of atom is on the order of MHz. But the linewidth of SPDC photon is on the order of THz. It is hard to realize the efficient coupling between the atom and the photon to transfer information. So preparing a narrow-band photon is a necessary work.The main contents and key points in this dissertation are as follows:1. Second harmonic generation with periodically poled potassium titanyl phosphate. We use CW laser and pulse laser to generation second harmonic respectively. Firstly, we experimentally demonstrate an efficient CW SHG at 780 nm wavelength with a first-order type-Ⅰphase matching PPKTP crystal in a ring cavity. At an input mode-matched power of 73mW, the power of generated UV radiation is 8.8mW with the net conversion of 12%. Secondly we report on the efficient frequency doubling of a femtosecond laser at 800 nm wavelength with type-Ⅱphase matching PPKTP crystals in a single-pass configuration. The normalized conversion efficiency of 0.36%W-1 cm-1 is obtained.2. Preparation of SPDC Photon Pairs in PPKTP. At second part we study the generation of a collinearly propagating photon pair by pumping a 2.12 mm long type-I phase matching bulk PPKTP crystal with CW laser. Using a single mode fiber as a spatial filter, we detect about 7400/s net coincidence counts with 3.58 mW pump power in a Hanbury-Brown-Twiss-type experiment. The estimated photon pair production rate is about 0.73 MHz/mW per second. At second part, we experimentally demonstrate an ultrabright two-photon source with a type-I bulk PPKTP. With the 390 nm CW laser generated from our home-made frequency doubler in a ring cavity as the pump, we detect about 340 k/s coincidence counts with a pump power of 0.11 mW in a Hanbury-Brown-Twiss-type experiment in a single-pass SPDC configuration, corresponding to the production rate of 94 MHz/mW with full bandwidth of 40 nm measured at FWHM. With a 3 nm interference filter, we detect about 11.5 k/s coincidence counts with pump power of 0.11 mW, which corresponds to the production rate of 4.3 MHz/mW/nm.3. Experimental measuring the coherence length of the single photon generated via a degenerated optical parametric oscillator far below threshold. We report on experimental measuring the coherence length of the single photon, which is generated via a degenerated OPO far below threshold. The bandwidth of the cavity measured is about 7.8 MHz and the measured coherence length of the single photon is about 90μm via a Michelson interferometer due to the multimode property of the photon generated in the experiment. We also do a raw estimation about the coherence length of the single photon. The estimated coherence length is about 110μm, which is close to the measured 90μm coherence length in the experiment.4. Preparation of multi-channel photon pairs in a periodically poled Potassium Titanyl Phosphate waveguide. We propose a possible way to generate multi-channel photon pairs by using a periodically poled Potassium Titanyl Phosphate (PPKTP) waveguide via SPDC. We discuss type-Ⅱand type-Ⅰphase matching cases with a pulsed and CW laser respectively. We could make a multi-channel photon pairs source which could provide these photon pairs to several communication couples at the same time. This is very promising in quantum information network.更多还原