Towards quantum-enhanced precision measurements： Promise and challenges

Quantum metrology holds the promise of improving the measurement precision beyond the limit of classical approaches.To achieve such enhancement in performance requires the development of quantum estimation theories as well as novel experimental techniques.In this article,we provide a brief review of some recent results in the field of quantum metrology.We emphasize that the unambiguous demonstration of the quantum-enhanced precision needs a careful analysis of the resources involved.In particular,the implementation of quantum metrology in practice requires us to take into account the experimental imperfections included,for example,particle loss and dephasing noise.For a detailed introduction to the experimental demonstrations of quantum metrology,we refer the reader to another article’Quantum metrology’in the same issue.     

Inspection of nano-sized SNOM-tips by optical far-field evaluation

High resolution optical microscopy has many interesting applications in solid state physics, low temperature physics, biology and semiconductor technology. Unfortunately, the lateral resolution of conventional microscopes is limited by the Rayleigh-limit. “Scanning nearfield optical microscopy” (SNOM) seems to be a promising new approach to characterize the properties of materials optically with a high lateral resolution of 50–100 nm. The most important part of such a microscope is the scanning probe (a special glass fiber tip). However, the quality of the optical fiber tip is of decisive importance. Since the production process of pulled and coated glass fiber tips is still highly empirical and error-prone, a technique would be useful to determine the tips’ quality before they are shipped to the user or mounted in the microscope. The tips’ apertures are smaller than λ/2 and therefore they cannot be measured in a non-destructive way by conventional optical microscopy. This paper discusses an easy and fast method for the optical characterization of common glass fiber SNOM tips. The effective aperture of the tip is measured from the far-field distribution of the emitted intensity recorded by a CCD target. A numerical model is introduced to solve this inverse task and a simple optical setup is presented to detect light emitted by the tip at an angle of up to 90° from the optical axis. Experimental investigation, near/far-field calculations and scanning electron microscope investigations show the working principle of this measurement technique for the analysis and evaluation of a typical nanostructured object.     

Optical Metrology by Fringe Processing on Independent Windows Using a Genetic Algorithm

We present a method to retrieve the phase of a fringe pattern based on the window fringe pattern demodulation technique (WFPD). The overlapped phase similarity criterion is avoided in the proposed method, and it is substituted by a second order smoothness criterion. The fringe processing on independent windows (FPIW) method can measure physical quantities from closed and near sub-sampled fringe patterns by a simplified cost or fitness function. The fringe image is divided into a set of partially overlapping windows. In these sub-images the estimated phase is modelled as a parametric analytic-function, and its parameters are optimized using a genetic algorithm (GA). This analytic-function is used to estimate the phase in the area framed by the window. Phases from all windows are sequentially spliced to retrieve the whole phase field. A media filter is applied over the entire phase field to smooth the irregularities that appear in the junctures between windows.     

Inverse projected-fringe technique based on multi projectors

The inverse projected-fringe technique based on multi projectors is proposed. By an absolute phase measurement on the master object, different inverse fringes are generated, for projectors placed in different directions. During the inspection process, inverse fringes are projected simultaneously. If the test object and the master object are identical, an optimized sine fringe is obtained on the camera. Otherwise, every faulty area of the test object causes distortions of the fringe. The deformations can be evaluated quantitatively by simple Fourier transformation and phase unwrapping. Therefore, we can complete the inspection of complex and discontinuous objects with only one fringe image, and solve the problems of shadow and break to a large extent, and consequently realize the fast on-line inspection. The principle of this technique is expatiated, and we prove the validity of it on the example of a two-projector system. The analysis of error and prerequisites of application are also presented.     

城市化进程中外来民工居住问题研究

外来民工的居住问题是影响城市化、外来民工市民化的一大阻碍．住宅业和城市化关系密切，相互促进．现阶段，住宅业的发展不适应城市化以及外来民工市民化的要求．城市化将给住宅业带来巨大的发展空间，同时也给住宅业的发展提出了更高的要求．住宅业要为城市化服务，积极配合城市化的发展．     

飞秒光梳和碘稳频532nm Nd:YAG激光频率的测量

报道了中国计量科学研究院研制的基于掺钛蓝宝石(Ti:Sapphire)锁模飞秒脉冲激光器的飞秒光学频率梳装置，并利用此装置测量了碘稳频532nm(¹²⁷I₂R(56)32-10) Nd∶YAG固体激光器的频率，结果为 563260223512991±20Hz,相对不确定度为3.6×10^-14.这一数值是直接溯源到铯原子微波频率基准的光学频率测量结果.     

数字散斑法在局域剪切带三维变形研究中的应用

在适当的温度、应变率和预变形下,合金材料的拉伸试验中,将会出现伴随应力锯齿形跌落的雪崩式剪切变形带,即波特文-勒夏特利埃(Portevin-Le Chatelier,PLC)效应。利用高速数字摄像系统(分辨力1000 frames/s)并结合数字散斑干涉法(Digital speckle pattern interferometry,DSPI)和数字散斑相关法设计了一套光学变形测量系统,实现了拉伸试验中对试件表面三维变形的实时、精确测量。利用该光学系统对铝铜合金试件在拉伸试验中产生的跳跃传播的局域剪切带瞬态成核过程进行捕捉。通过结合数字散斑相关法得到的面内变形定量结果和数字散斑干涉法得到的表现离面变形的条纹图,再现了剪切变形带成核和传播瞬间的三维变形过程。     

Two-dimensional windowed Fourier transform for fringe pattern analysis: Principles, applications and implementations

Fringe patterns from optical metrology systems need to be demodulated to get the desired parameters. Two-dimensional windowed Fourier transform is chosen for the determination of phase and phase derivatives. Two algorithms, one based on filtering and the other based on similarity measure, are developed. Some applications based on these two algorithms are explored, including strain determination, phase unwrapping, phase-shifter calibration, fault detection, edge detection and fringe segmentation. Various examples are given to demonstrate the ideas. Finally implementations of these algorithms are addressed. Most of the work has appeared in various papers and its originality is not claimed. Instead, this paper gives an overview and more insights of our work on windowed Fourier transform.     

Minimizing Labor Requirements in a Periodic Vehicle Loading Problem

In this paper, we address a logistics problem that a manufacturer of auto parts in the north of Spain described to the authors. The manufacturer stores products in its warehouse until customers retrieve them. The customers and the manufacturer agree upon an order pickup frequency. The problem is to find the best pickup schedule, which consists of the days and times during the day that each customer is expected to retrieve his/her order. For a given planning horizon, the optimization problem is to minimize the labor requirements to load the vehicles that the customers use to pick up their orders. Heuristically, we approach this situation as a decision problem in two levels. At the first level, customers are assigned to a calendar, consisting of a set of days with the required frequency during the planning horizon. Then, for each day, the decision at the second level is to assign each customer to a time slot. The busiest time slot determines the labor requirement for a given day. Therefore, once customers have been assigned to particular days in the planning horizon, the second-level decision is a multiprocessor scheduling problem, where each time slot is the equivalent of a processor, and where the objective is to minimize the makespan. A metaheuristic procedure is developed for the problem of minimizing labor requirements in this periodic vehicle-loading problem and artificial as well as real data are used to assess its performance.