长距离长期稳定的量子密钥分发系统

介绍了最近完成的长距离长期稳定的量子密钥分发系统.该系统利用往返光路补偿光纤偏振 抖动和相位漂移的原理,采用结电容平衡魔T网络耦合的单光子探测技术,在506km单模 光纤中实现了长时间（大于12h）稳定的量子密钥分发实验.单脉冲平均光子数为007, 误码率为4%,其中单光子探测器的探测效率大于5%,单脉冲暗计数低于29×10^{-6. 关键词： 量子保密通信 量子密钥分发 单光子探测}     

A Twisted Bay‐Substituted Quaterrylene Phosphorescing in the NIR Spectral Region

The preparation of the first soluble quaterrylene derivative featuring peripheral tert‐butyl substituents and sterically hindering, core‐anchored triflate groups has been achieved. This involves a facile synthetic route based on an oxidative coupling of perylene precursors in the presence of H₂O₂ as oxidant. The steric hindrance between the TfO substituents at the central bay position of the quaterrylene board triggers a strong deformation of the central perylene planarity, which forces the quaterrylene platform to adopt a twisted geometry as shown by X‐ray analysis. Exceptionally, photophysical investigations show that the core‐twisted quaterrylene phosphoresces in the NIR spectral region at 1716 nm. Moreover, third‐order nonlinear optical measurements on solutions and thin film containing the relevant molecule showed very large second hyperpolarizability values, as predicted by theoretical calculations at the CAM ‐B3LYP /6‐31G** level of theory, making this material very appealing for photonic applications.     

Single-photon all-optical switching using coupled microring resonators

We study the nonlinear phase response of a microring resonator coupled to a bus waveguide and the use of this nonlinear phase shift to store information in the microring resonator and enhance the switching characteristics of a Mach-Zehnder interferometer (MZI). By introducing coupling between adjacent microring resonators, the switching characteristics of the MZI can be exponentially enhanced as a function of the number of microring resonators, when compared to the linear enhancement for uncoupled resonators. With only a few moderate-finesse microring resonators, the switching power can be reduced to attowatt level, allowing for photonic switching devices that operate at single-photon level in ordinary optical waveguides.      

超导单光子探测器件直流特性研究

超导单光子探测技术是基于超薄超导薄膜的非平衡态热电子效应的一种新型的单光子探测方法。超导单光子探测器(SNSPD)的计数率可达到GHz,时间抖动小于100ps,因而在未来量子通信系统中有着广阔的应用前景。介绍了NbN超导单光子探测器件的工作原理和器件超导性能测试系统;测试了超导单光子探测器件的电阻-温度、电流-电压等特性。并对测试结果进行了分析和讨论。     

Temperature and current sensitivity extraction of optical superconducting transition-edge sensors based on a two-fluid model

Optical superconducting transition-edge sensor(TES) has been widely used in quantum information, biological imaging, and fluorescence microscopy owing to its high quantum efficiency, low dark count, and photon number resolving capability. The temperature sensitivity(α_I) and current sensitivity(β_I) are important parameters for optical TESs, which are generally extracted from the complex impedance. Here we present a method to extract α_I and β_I based on a twofluid model and compare the calculated current–voltage curves, pulse response, and theoretical energy resolution with the measured ones. This method shows qualitative agreement that is suitable for further optimization of optical TESs.     

三苯胺-吡啶衍生物的三光子吸收及光限幅特性

合成了3个三苯胺-吡啶衍生物4-乙烯基吡啶-4'-(N,N-二苯胺基)苯(PPAB)、三[4-(4-吡啶乙烯基)苯]胺(TPPA)和4-(对-甲基-乙烯基吡啶碘盐)-4'-(N,N-二苯胺基)苯(PBPI),研究了它们的单光子荧光和三光子荧光性质.在1310nm飞秒激光激发下,化合物PPAB,PBPI and TPPA在二氯甲烷溶液中发出很强的三光子上转换荧光,荧光峰分别位于648,625,696nm.用飞秒Ti:Sapphire激光器非线性透过率法测得3个化合物在1310nm三光子吸收截面分别为1.91×10-79,3.46×10-79,3.64×10-79cm6·s2,它们具有很强的三光子吸收和光限幅效应.     

Fast Photoresponse and Long Lifetime UV Photodetectors and Field Emitters Based on ZnO/Ultrananocrystalline Diamond Films

We have designed photodetectors and UV field emitters based on a combination of ZnO nanowires/nanorods (ZNRs) and bilayer diamond films in a metal–semiconductor–metal (MSM) structure. The ZNRs were fabricated on different diamond films and systematic investigations showed an ultra‐high photoconductive response from ZNRs prepared on ultrananocrystalline diamond (UNCD) operating at a lower voltage of 2 V. We found that the ZNRs/UNCD photodetector (PD) has improved field emission properties and a reduced turn‐on field of 2.9 V μm^?1 with the highest electron field emission (EFE) by simply illuminating the sample with ultraviolet (UV) light. The photoresponse (I_photo/I_dark) behavior of the ZNRs/UNCD PD exhibits a much higher photoresponse (912) than bare ZNRs (229), ZNRs/nanocrystalline diamond (NCD; 518), and ZNRs/microcrystalline diamond (MCD; 325) under illumination at λ=365 nm. A photodetector with UNCD films offers superior stability and a longer lifetime compared with carbon materials and bare ZNRs. The lifetime stability of the ZNRs/UNCD‐based device is about 410 min, which is markedly superior to devices that use bare ZNRs (92 min). The ZNRs/UNCD PD possesses excellent photoresponse properties with improved lifetime and stability; in addition, ZNRs/UNCD‐based UV emitters have great potential for applications such as cathodes in flat‐panel displays and microplasma display devices.     

Sustained photon pulse revivals from inhomogeneously broadened spin ensembles

A very promising recent trend in applied quantum physics is to combine the advantageous features of different quantum systems into what is called “hybrid quantum technology”. One of the key elements in this new field will have to be a quantum memory enabling to store quanta over extended periods of time. Systems that may fulfill the demands of such applications are comb‐shaped spin ensembles coupled to a cavity. Due to the decoherence induced by the inhomogeneous ensemble broadening, the storage time of these quantum memories is, however, still rather limited. Here we demonstrate how to overcome this problem by burning well‐placed holes into the spectral spin density leading to spectacular performance in the multimode regime. Specifically, we show how an initial excitation of the ensemble leads to the emission of more than a hundred well‐separated photon pulses with a decay rate significantly below the fundamental limit of the recently proposed “cavity protection effect”.

     

Conjugated Polymer Nanoparticle‐Triplet Emitter Hybrids in Aqueous Dispersion: Fabrication and Fluorescence Quenching Behavior

Conjugated polymer nanoparticles based on poly[9,9‐bis(2‐ethylhexyl)fluorene] and poly[N‐(2,4,6‐trimethylphenyl)‐N,N‐diphenylamine)‐4,4′‐diyl] are fabricated using anionic surfactant sodium dodecylsulphate in water by miniemulsion technique. Average diameters of polyfluorene and polytriarylamine nanoparticles range from 70 to 100 and 100 to 140 nm, respectively. The surface of the nanoparticles is decorated with triplet emitting dye, tris(2,2′‐bipyridyl)ruthenium(II) chloride. Intriguing photophysics of aqueous dispersions of these hybrid nanoparticles is investigated. Nearly 50% quenching of fluorescence is observed in the case of dye‐coated polyfluorene nanoparticles; excitation energy transfer is found to be the dominant quenching mechanism. On the other hand, nearly complete quenching of emission is noticed in polytriarylamine nanoparticle‐dye hybrids. It is proposed that the excited state electron transfer from the electron‐rich polytriarylamine donor polymer to Ru complex leads to the complete quenching of emission of polytriarylamine nanoparticles. The current study offers promising avenues for developing aqueous solution processed‐electroluminescent devices involving a conjugated polymer nanoparticle host and Ru or Ir‐based triplet emitting dye as the guest.