基于局域操作下的两量子比特混态纠缠蒸馏实验研究

最大纠缠态在量子信息传输和处理过程中是最重要的资源之一，因此从退化的纠缠态中提炼出最大纠缠态一直是量子信息基础研究中的一个重要课题．根据Verstraete F等人在Phys．Rev．A，2001，64：010101（R）上提出的有效的方法，文章作者在实验上证明了基于局域操作下的两种形式的两量子比特混态纠缠蒸馏最佳协议．从原则上讲，文章的实验也可以容易地应用于任意两量子比特部分混合态的纠缠蒸馏．此外，作者还对经过蒸馏的第一类混合量子态进行Clauser-Home-Shimmony-Holt（CHSH）不等式的检测，以验证它的“隐藏非局域性”。     

Optoelectronic properties of bottom gate-defined in-plane monolayer WSe_2 p–n junction

Monolayer transition-metal dichalcogenides(TMDs) are considered to be fantastic building blocks for a wide variety of optical and optoelectronic devices such as sensors, photodetectors, and quantum emitters, owing to their direct band gap,transparency, and mechanical flexibility. The core element of many conventional electronic and optoelectronic devices is the p–n junction, in which the p-and n-types of the semiconductor are formed by chemical doping in different regions.Here, we report a series of optoelectronic studies on a monolayer WSe_2 in-plane p–n photodetector, demonstrating a lowpower dissipation by showing an ambipolar behavior with a reduced threshold voltage by a factor of two compared with the previous results on a lateral electrostatically doped WSe_2 p–n junction. The fabrication of the device is based on a polycarbonates(PC) transfer technique and hence no electron-beam exposure induced damage to the monolayer WSe_2 is expected. Upon optical excitation, the photodetector demonstrates a photoresponsivity of 0.12 mA·W~(-1) and a maximum external quantum efficiency of 0.03%. Our study provides an alternative platform for a flexible and transparent twodimensional photodetector, from which we expect to further promote the development of next-generation optoelectronic devices.     

Gap plasmon-enhanced photoluminescence of monolayer MoS_2 in hybrid nanostructure

Monolayer transition-metal dichalcogenides(TMDs) have attracted a lot of attention for their applications in optics and optoelectronics.Molybdenum disulfide(MoS_2),as one of those important materials,has been widely investigated due to its direct band gap and photoluminescence(PL) in visible range.Owing to the fact that the monolayer MoS_2 suffers low light absorption and emission,surface plasmon polaritons(SPPs) are used to enhance both the excitation and emission efficiencies.Here,we demonstrate that the PL of MoS_2 sandwiched between 200-nm-diameter gold nanoparticle(Au NP) and 150-nm-thick gold film is improved by more than 4 times compared with bare MoS_2 sample.This study shows that gap plasmons can possess more optical and optoelectronic applications incorporating with many other emerging two-dimensional materials.     

自发参量下转化光子对的轨道角动量

自发参量下转换过程中产生的光子对的轨道角动量是纠缠的.我们计算了薄晶体产生的光子对轨道角动量的相对振幅.结果显示相对振幅依赖于两个拉盖尔系数l和p.我们还讨论了实验中用来模式分析的全息片和单模光纤的影响.我们认为下转换光子对轨道角动量的无限维在实际中只有有限维是可用的.     

表面等离子体辅助光传送过程的实验研究

实验证明，在表面等离子体辅助传送过程中，纠缠可以从光子转移到表面等离子体，也就是说这种大量电子（10的10次方）的集体振荡也具有量子特性。     

FDTD Studies of Metallic Cylinder Arrays： Plasmon Waveguide and Y-Splitter

The plasmon waveguide based on double chain of gold cylinders is studied using the finite-difference time-domain method （FDTD）. The wavelength of the incident Gaussian beam ranges from 650 to 1200nm, and the corresponding attenuation factors are calculated. We also present a Y-splitter with 90° splitting angle, each branch in the form of double chains. The transmission efficiencies for different wavelengths are evaluated.     

Enhancement of the second harmonic generation from monolayer WS2 coupled with a silica microsphere

Monolayer transition metal dichalcogenides (TMDs) are widely used for integrated optical and photoelectric devices. Owing to their broken inversion symmetry, monolayer TMDs have a large second-order optical nonlinearity. However, the optical second-order nonlinear conversion efficiency of monolayer TMDs is still limited by the interaction length. In this work, we theoretically study the second harmonic generation (SHG) from monolayer tungsten sulfide (WS₂) enhanced by a silica microsphere cavity. By tuning the position, size, and crystal orientation of the material, second-order nonlinear coupling can occur between the fundamental pump mode and different second harmonic cavity modes, and we obtain an optimal SHG conversion efficiency with orders of magnitude enhancement. Our work demonstrates that the microsphere cavity can significantly enhance SHG from monolayer 2D materials under flexible conditions.     

Engineering of Multi-Dimensional Entangled States of Photon Pairs Using Hyper-Entanglement

Multi-dimensional entangled states have been proven to be more powerful in some quantum information processes. Down-converted photons from spontaneous parametric down-conversion are used to engineer multi-dimensional entangled states. A kind of multi-degree multi-dimensional Greenberger-Horne-Zeilinger states can also be generated. The hyper-entangled photons are entangled in energy-time, polarization and orbital angular momentum, which is proven to be useful to increase the dimension of systems and to investigate higher-dimensional entangled states.     

近场研究表面等离子体在银纳米线上的传输

通过双探针近场光学扫描显微镜在银纳米线上实现近场激发和近场收集表面等离子体,用一个探针在银纳米线的一端近场激发表面等离子体,另一个探针近场探测银纳米线上的表面等离子体强度分布,得到强度分布图.强度分布图显示表面等离子体在银纳米线的一端被有效激发并且有一部分表面等离子体沿着银纳米线和基底的界面传播到了另一端.用有限元法对银纳米线内的传播模式进行数值模拟,结果显示银纳米线内存在两种表面等离子体传播模式,分别为基模和高阶模.沿着银纳米线和基底介质之间传输的基模表面等离子体由于传输环境稳定,散射损耗小,实际传输长度接近模式传输长度,达10μm以上;而高阶模表面等离子体由于部分裸露在空气中受表面缺陷散射的影响,散射损耗大,实际传输长度远小于模式传输长度.研究表明:以能量高度束缚的基模表面等离子体作为载体,不仅可以实现低损耗传输,还可以减小集成器件之间的信号串扰,有效提高信息传输的安全性,在集成光学中具有重要应用.