通过相位偏移来测量弱值

几年前,由Aharonov, Albert和Vaidman等提出了量子力学中对于可观测量的弱测量理论(weak measurement). 弱测量过程中测量系统与态之间的相互作用相当弱,从而不会导致态的塌缩.     

用周期性极化介质制备高亮度纠缠光源

在量子信息中,纠缠源处于十分重要的地位.目前常用的产生纠缠光源的方法是用自发参量下转换过程产生的双光子态,但其效率很低,一般需要高功率激光器泵浦.本文将用周期性极化介质,在低功率泵浦下获取高亮度的纠缠光源.由于采用了准位相匹配技术能有效的利用较高的非线性系数,加上周期性的结构,使得转换效率大大提高.实验上我们发现其转换效率较之传统的块状晶体得到了极大的改善,有数量级的提高!     

双光子"which way"干涉实验

干涉源于不可分辨,可分辨性会导致干涉条纹的下降.在我们进行的双光子"which way"干涉实验中,我们用偏振自由度标记参量下转换产生的两个光子经过的路径.这一标记会导致光子经过的路径可区分性的变化,从而导致干涉可见度的变化.实验证实了这一推断.     

实验检验双光子的几何相位

Pancharatnam在研究两束光干涉时提出的几何相位的概念;紧接着Berry发现了量子系统在循环绝热演化下的几何相位.在光子系统中,实验上已经验证了经典光和单光子的几何相位,并观察到几何相位的大小与循环演化过程有关.对于双光子,其几何相位在相同的循环演化下是单光子两倍.我们提出了一种简单的实验方案来观察双光子的几何相位.实验中,通过光路的设计排除了由于光程改变引起的相位改变,直接检测由于几何相位的不同引起的双光子干涉.     

Temperature-free mass tracking of a levitated nanoparticle

Mass measurement is an essential analytical tool in the characterization of materials. Here we present a method for measuring the mass of an individual nanoparticle which has a fg-level mass. This method enables a temperatureindependent mass measurement with the assistance of a sinusoidal electrostatic driving force. With this approach, we successfully track the change in properties of an optically levitated nanoparticle, such as mass, temperature, and electric charge, with air pressure. An abru...     

A Four-Dimensional Measurement Scheme for Single Photon Time-Polarization

We propose an experimental scheme to realize the four-dimensional projective measurements tor a single photon. The photon polarization and time-energy provide the four-dimensional Hilbert space. Based on this scheme, we suggest an experiment to test the violation of Bell inequalities of four-dimensional systems. In addition, by virtue of a maximally entangled biphoton state, we also show that it is possible to construct a quantum key distribution channel that can provide two-bit key with one pair of entangled photons.     

Photoluminescence from site-selected coupling between quantum dots and microtoroid cavities

By using CdSe/ZnS quantum dots （QDs）, we study the effect of cavity quantum electrodynamics on the coupling of the microtoroid cavity. When with whispering gallery （WG） modes, the microtoroid cavity demonstrates high quality factor and small mode volume at visible wavelengths. Accordingly, fiber tapers allow QDs to adhere into the cavity and further permit the control of site-selected coupling. From the luminescence spectra, QDs are modulated effectively by cavity modes, Variable modulations are observed by changing QD coupling conditions. Therefore, based on experimental and theoretical research, strong and tunable Purcell enhancement can be realized by this system.     

A “Which Way” Experiment of Two-Photon Interference

It is well known that the indistinguishability of particles causes interference. We give a “which way” experiment of two-photon interference marked with polarization. The result shows that the greater the distinguishability of the path by which two-photon passes, the lower the fringe visibility will be, and this phenomenon will disappear when the path becomes completely distinguishable.     

基于金刚石氮-空位色心的温度传感

在各种物理量中,温度是最直观和最普遍的量.温度的剧烈变化通常意味着物体的物理性质出现波动,因此在各个领域中温度往往是重要的指标.随着科学技术的发展,许多领域研究和应用的尺度越来越小,然而在小于10μm的空间尺度内还没有通用的温度测量方法.除了空间分辨率的要求,传感器在测量过程中不应该对被测对象有巨大影响,金刚石氮-空位(nitrogen vacancy, NV)色心是一种稳定的发光缺陷,通过对其能谱和电子自旋量子态的测量,可以获得其附近温度、电磁场等物理量的信息.由于金刚石的化学特性稳定和热导率高,可以进行纳米尺度的非破坏性测量.它对细胞无毒,也可以用于生命领域的研究.此外,根据金刚石的特性, NV色心可以与光纤、扫描显微镜等技术结合,实现不同场景中的温度测量.本文将介绍金刚石NV色心的温度特性、测温原理及其在相关领域的应用.