Generation and application of twin beams from an optical parametric oscillator including an alpha-cut KTP crystal

Measurement slight amounts of absorption of light with accuracy beyond the standard quantum limit has been experimentally demonstrated. The quantum-correlated twin beams used in the measurement were generated from a nondegenerate optical parametric oscillator including an alpha-cut KTiOPO(4) crystal pumped by an intracavity frequency-doubled Nd:YAG laser. The noise in the intensity difference between the twin beams was reduced by 88% below the standard quantum limit (SQL). The signal-to-noise ratio was improved by 7 dB with respect to the SQL of the total light employed in the experiment and by 4 dB with respect to that of the signal light.     

QND measurements for future gravitational-wave detectors

Second-generation interferometric gravitational-wave detectors will be operating at the Standard Quantum Limit (SQL), a sensitivity limitation set by the trade off between measurement accuracy and quantum back action, which is governed by the Heisenberg Uncertainty Principle. We review several schemes that allows the quantum noise of interferometers to surpass the SQL significantly over a broad frequency band. Such schemes may be an important component of the design of third-generation detectors.     

Exponential speedup with a single bit of quantum information: measuring the average fidelity decay

We present an efficient quantum algorithm to measure the average fidelity decay of a quantum map under perturbation using a single bit of quantum information. Our algorithm scales only as the complexity of the map under investigation. Thus for those maps admitting an efficient gate decomposition, it provides an exponential speedup over known classical procedures. Fidelity decay is important in the study of complex dynamical systems, where it is conjectured to be a signature of eigenvector statistics. Our result also illustrates the role of chaos in the process of decoherence.     

Diamagnetic levitation of a milligram-scale silica using permanent magnets for the use in a macroscopic quantum measurement

Verification of macroscopic quantum mechanics requires that the position measurement accuracy of mirrors of various mass scales reach the Standard Quantum Limit (SQL) derived from Heisenberg's uncertainty principle. At mg-scale, thermal noise of the suspension wire of the mirror is an issue to reach the SQL. We propose to use a magnetic levitation system consisting of permanent magnets and yokes, noting the fact that a silica mirror is diamagnetic, and have succeeded in the experimental verification to levitate a 0.1-1 mg silica mass. This is the first demonstration of the levitation system with this mass scale and this magnetic susceptibility scale using permanent magnets as far as we know. We also estimated major noise sources for a 0.1 mg silica mirror and found the noise level to be lower than the SQL at 400 Hz-18 kHz. In conclusion, the levitation system of a mg-scale mirror for the use in a macroscopic quantum measurement was realized.     

Quantum information processing in optical images

Optical images can be used to transport, store and process information in a parallel way. We discuss different results obtained in the domain of ‘quantum imaging’, aiming at exploiting at the same time the quantum properties of optical images and their intrinsic parallelism. We define the notion of standard quantum limit (SQL) in optical resolution, set by the quantum noise of usual coherent light, and show that it can be much lower than the diffraction limit. We also prove that this limit can be circumvented by especially designed nonclassical and multimode light. We present an experiment showing that OPOs oscillating inside an exactly confocal cavity actually produce such transverse multimode nonclassical light. We finally describe another experiment which has surpassed the SQL in the case of beam positioning, both in the 1D and 2D cases.     

改进退火遗传算法在SQL数据挖掘参数优化中的应用

针对SQL数据挖掘在复杂动力学系统故障诊断中的模式分类问题,以决策树参数优化为例,开展SQL数据挖掘分类算法参数优化研究。目前数据挖掘中的各类算法参数往往根据经验值设定,预测精度不高;只用遗传算法进行参数优化,分类预测结果容易发生振荡和早熟现象。采用改进的退火遗传算法对SQL数据挖掘中的决策树算法参数进行优化,解决了人工经验设置参数效率低下、精度不高的问题,同时实现了全局搜索,快速收敛到全局最优解。     

Improving optomechanical gyroscopes by coherent quantum noise cancellation processing

Coherent quantum noise cancellation(CQNC) method is used to beat standard quantum limit(SQL) for improving the performance of quantum optomechanical gyroscopes. The protocol for realizing CQNC is achieved by constructing an effective negative mass mechanical oscillator, which is simulated by an ancillary cavity. This oscillator shows an antiresponse relative to that of a real mechanical oscillator. Thus, the optomechanical back-action noise is counteracted or restrained, and we could increase our signal by increasing the coupling strength without increasing the noise.     

Determination of the elementary charge and the quantum metrological triangle experiment

The elementary charge e is of fundamental importance in physics. The determination of its value, which is closely linked to progress of the measurement techniques, started in the beginning of the twentieth century and is still on-going. Today, in the frame of the CODATA adjustment, the evaluation of the fundamental constant, e, is derived from a complex calculation and is no more related to a single experiment. But the development of single electron tunneling (SET) devices, started in the early 90s, has opened the path towards modern metrological systems as quantum current sources. Thus a new direct determination of e is possible by implementing an electron pump and the set-up of the quantum metrological triangle (QMT) in combination with the experiments linking mechanical and electrical units. Furthermore, we show how the QMT experiment can contribute to the establishment of a new system of units based on fundamental constants of physics.     

Quantum Image Steganography and Steganalysis Based On LSQu-Blocks Image Information Concealing Algorithm

Quantum steganography can solve some problems that are considered inefficient in image information concealing. It researches on Quantum image information concealing to have been widely exploited in recent years. Quantum image information concealing can be categorized into quantum image digital blocking, quantum image stereography, anonymity and other branches. Least significant bit (LSB) information concealing plays vital roles in the classical world because many image information concealing algorithms are designed based on it. Firstly, based on the novel enhanced quantum representation (NEQR), image uniform blocks clustering around the concrete the least significant Qu-block (LSQB) information concealing algorithm for quantum image steganography is presented. Secondly, a clustering algorithm is proposed to optimize the concealment of important data. Finally, we used Con-Steg algorithm to conceal the clustered image blocks. Information concealing located on the Fourier domain of an image can achieve the security of image information, thus we further discuss the Fourier domain LSQu-block information concealing algorithm for quantum image based on Quantum Fourier Transforms. In our algorithms, the corresponding unitary Transformations are designed to realize the aim of concealing the secret information to the least significant Qu-block representing color of the quantum cover image. Finally, the procedures of extracting the secret information are illustrated. Quantum image LSQu-block image information concealing algorithm can be applied in many fields according to different needs.     

Impact of optical antenna and plasmonics on infrared imagers

The advent of nanophotonics allows devising and fabricating optical antenna as the advanced optical structures that can enhance light–matter interaction in quantum structures such as quantum wells. Improving infrared photodetector performance is discussed theoretically in this paper. We also investigate our recent demonstration of optical antenna integrated on quantum well infrared photodetector which improves the performance of the detector as can be evidence in responsivity of the detector.     

Quantized dynamics of a coherent capacitor

A quantum coherent capacitor subject to large amplitude pulse cycles can be made to emit or reabsorb an electron in each half cycle. Quantized currents with pulse cycles in the GHz range have been demonstrated experimentally. We develop a nonlinear dynamical scattering theory for arbitrary pulses to describe the properties of this very fast single electron source. Using our theory we analyze the accuracy of the current quantization and investigate the noise of such a source. Our results are important for future scientific and possible metrological applications of this source.     

Quantum improvement of time transfer between remote clocks

Exchanging light pulses to perform accurate space-time positioning is a paradigmatic issue of physics. It is ultimately limited by the quantum nature of light, which introduces fluctuations in the optical measurements and leads to the so-called standard quantum limit (SQL). We propose a new scheme combining homodyne detection and mode-locked femtosecond lasers that lead to a new SQL in time transfer, potentially reaching the yoctosecond range (10(-21)-10(-24) s). We demonstrate that this already very low SQL can be overcome using appropriately multimode squeezed light. Benefitting from the large number of photons and from the optimal choice of both the detection strategy and of the quantum resource, the proposed scheme represents a significant potential improvement in space-time positioning.     

Algorithm for determining the aerodynamic characteristics of a freely flying object from discrete data of ballistic experiment. Part 2

In part 1 of this paper, an algorithm for numerically solving the inverse problem of motion of a solid through the atmosphere is described that constitutes the basis for identifying the aerodynamic characteristics of an object from trajectory data and the respective identification procedure is presented. In part 2, methods evaluating the significance of desired parameters and adequacy of a mathematical model of motion, approaches to metrological certification of experimental equipment, and results of testing the algorithm are discussed.     

Algorithm for determining the aerodynamic characteristics of a freely flying object from discrete data of ballistic experiment. Part I

In part 1 of this paper, an algorithm for numerically solving the inverse problem of motion of a solid through the atmosphere is described that constitutes the basis for identifying the aerodynamic characteristics of an object from trajectory data and the respective identification procedure is presented. In part 2, methods evaluating the significance of desired parameters and adequacy of a mathematical model of motion, approaches to metrological certification of experimental equipment, and results of testing the algorithm are discussed.     

Entanglement of macroscopic test masses and the standard quantum limit in laser interferometry

We show that the generation of entanglement of two heavily macroscopic mirrors is feasible with state of the art techniques of high-precision laser interferometry. The basis of such a demonstration would be a Michelson interferometer with suspended mirrors and simultaneous homodyne detections at both interferometer output ports. We present the connection between the generation of entanglement and the standard quantum limit (SQL) for a free mass. The SQL is a well-known reference limit in operating interferometers for gravitational-wave detection and provides a measure of when macroscopic entanglement can be observed in the presence of realistic decoherence processes.     

Spin-filtering and charge- and spin-switching effects in a quantum wire with periodically attached stubs

Spin-dependent electron transport in a periodically stubbed quantum wire in the presence of Rashba spin-orbit interaction (SOI) is studied via the nonequilibrium Green’s function (GF) method combined with the Landauer-Büttiker formalism. By comparing with a straight Rashba quantum wire, the magnitude of spin conductance can be enhanced obviously. In addition, the charge and spin switching can also be found in the considered system. The mechanism of these transport properties is revealed by analyzing the total charge density and spin-polarized density distributions in the stubbed quantum wire. Furthermore, periodic spin-density islands with high polarization are also found inside the stubs, owing to the interaction between the charge density islands and the Rashba SOI-induced effective magnetic field. These interesting findings may be useful in further understanding of the transport properties of low-dimensional systems and in devising an all-electrical multifunctional spintronic device based on the proposed structure.     

Algorithm for reconstruction of digital holograms with adjustable magnification

A new algorithm that allows for reconstruction of digital holograms with adjustable magnification is proposed. The algorithm involves two reconstruction steps implemented by a conventional single Fourier-transform algorithm. The advantages of the algorithm lie in its adaptability to various object sizes and recording distances as well as in its capability to maintain the pitch of a reconstructed image, independent of the reconstruction distance and wavelength for objects larger than a CCD. The feasibility of the algorithm is demonstrated by experiments. The algorithm is especially useful for reconstructing color holograms and for metrological applications.     

Features in atomic force microscopy studies of dielectric surfaces

To improve the accuracy of AFM measurements in air and the reproducibility of results, a clean room-based metrological facility has been designed and built. The main function of the facility is to control temperature and humidity in an operation zone in various combinations and to maintain them with high accuracy. Measurements under controlled conditions are particularly important for dielectric materials. It has been shown that special procedures allow one to avoid disturbances caused by static charges on the surface under study, i.e., to remove the already accumulated charge and prevent its appearance during experiments. The use of the proposed procedures makes it possible to adequately study the features of the dielectric surface relief at micro-and nanoscale levels.     

Real-Code Genetic Algorithm for Ground State Energies of Hydrogenic Donors in GaAs-(Ga,Al)As Quantum Dots

We present a global optimization method, called the real-code genetic algorithm (RGA), to the ground state energies. The proposed method does not require partial derivatives with respect to each variational parameter or solving an eigenequation, so the present method overcomes the major difficulties of the variational method. RGAs also do not require coding and encoding procedures, so the computation time and complexity are reduced. The ground state energies of hydrogenic donors in GaAs-(Ga,Al)As quantum dots have been calculated for a range of the radius of the quantum dot radii of practical interest. They are compared with those obtained by the variational method. The results obtained demonstrate the proposed method is simple, accurate, and easy implement.