Saddlepoint approximation for Student's t-statistic with no moment conditions

A saddlepoint approximation of the Student's t-statistic was derived by Daniels and Young [Biometrika 78 (1991) 169-179] under the very stringent exponential moment condition that requires that the underlying density function go down at least as fast as a Normal density in the tails. This is a severe restriction on the approximation's applicability. In this paper we show that this strong exponential moment restriction can be completely dispensed with, that is, saddlepoint approximation of the Student's t-statistic remains valid without any moment condition. This confirms the folklore that the Student's t-statistic is robust against outliers. The saddlepoint approximation not only provides a very accurate approximation for the Student's t-statistic, but it also can be applied much more widely in statistical inference. As a result, saddlepoint approximations should always be used whenever possible. Some numerical work will be given to illustrate these points.Comment: Published at http://dx.doi.org/10.1214/009053604000000742 in the Annals of Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical Statistics (http://www.imstat.org

Experimental quantum key distribution with active phase randomization

Phase randomization is an important assumption made in many security proofs of practical quantum key distribution (QKD) systems. Here, we present the first experimental demonstration of QKD with reliable active phase randomization. One key contribution is a polarization-insensitive phase modulator, which we added to a commercial phase-coding QKD system to randomize the global phase of each bit. We also proposed a simple but useful method to verify experimentally that the phase is indeed randomized. Our result shows very low QBER (<1%). We expect this active phase randomization process to be a standard part in future QKD set-ups due to its significance and feasibility.Comment: 3 pages, 3 figures, RevTE

Blind Image Restoration via the Integration of Stochastic and Deterministic Methods

This paper addresses the image restoration problem which remains a significant field of image processing. The fields of experts- (FoE-) based image restoration has been discussed and some open issues including noise estimation and parameter selection have been approached. The stochastic method FoE performs fairly well; meanwhile it might also produce unsatisfactory outcome especially when the noise is grave. To improve the final performance, we introduce the integration with deterministic method K-SVD. The FoE-treated image has been used to obtain the dictionary, and with the help of sparse and redundant representation over trained dictionary, the K-SVD algorithm can dramatically solve the problem, even though the pretreated result is of poor quality under severe noise condition. The experimental results via our proposed method are demonstrated and compared in detail. Meanwhile the test results from both qualitative and quantitative aspects are given, which present the better performance over current state-of-art related restoration algorithms

Quantum key distribution with "dual detectors"

To improve the performance of a quantum key distribution (QKD) system, high speed, low dark count single photon detectors (or low noise homodyne detectors) are required. However, in practice, a fast detector is usually noisy. Here, we propose a "dual detectors" method to improve the performance of a practical QKD system with realistic detectors: the legitimate receiver randomly uses either a fast (but noisy) detector or a quiet (but slow) detector to measure the incoming quantum signals. The measurement results from the quiet detector can be used to bound eavesdropper's information, while the measurement results from the fast detector are used to generate secure key. We apply this idea to various QKD protocols. Simulation results demonstrate significant improvements in both BB84 protocol with ideal single photon source and Gaussian-modulated coherent states (GMCS) protocol; while for decoy-state BB84 protocol with weak coherent source, the improvement is moderate. We also discuss various practical issues in implementing the "dual detectors" scheme.Comment: 22 pages, 9 figure

Serum cytokine profiling analysis for zheng differentiation in chronic hepatitis B

Approval document of the research protocol by the Medical Ethics Committee of Shuguang Hospital

(E)-3-(4-Hydr­oxy-3-methoxy­benzyl­idene)-4-(4-hydroxy­phen­yl)pyrrolidin-2-one

The title compound, C18H17NO4, was isolated from an ethanol extract of Ophiopogon japonicus. The dihedral angle between the 4-hydroxy-3-methoxyphenyl ring and the pyrrolidine ring is 17.4 (1)°. The 4-hydroxyphenyl ring makes a dihedral angle of 69.74 (6)° with the least-squares plane through the 4-hydroxy-3-methoxyphenyl ring and the pyrrolidine ring. The conformation of the pyrrolidine fragment is similar to a T-form. The crystal structure is stabilized by inter­molecular N—H⋯O and O—H⋯O hydrogen bonds

Slow light by coherent hole burnings

We show that the simultaneous application of a copropagating saturating pump and a counterpropagating coherent beam can be used to burn a narrow spectral hole within the absorption line of the optical transition in a Doppler-broadened medium. The large index of refraction of this hole slows down a light pulse by a factor of about 104. In addition, we propose a method to create two-color slow light pulses with simultaneous gain by employing a bichromatic field to saturate the medium

Practical Decoy State for Quantum Key Distribution

Decoy states have recently been proposed as a useful method for substantially improving the performance of quantum key distribution. Here, we present a general theory of the decoy state protocol based on only two decoy states and one signal state. We perform optimization on the choice of intensities of the two decoy states and the signal state. Our result shows that a decoy state protocol with only two types of decoy states--the vacuum and a weak decoy state--asymptotically approaches the theoretical limit of the most general type of decoy state protocols (with an infinite number of decoy states). We also present a one-decoy-state protocol. Moreover, we provide estimations on the effects of statistical fluctuations and suggest that, even for long distance (larger than 100km) QKD, our two-decoy-state protocol can be implemented with only a few hours of experimental data. In conclusion, decoy state quantum key distribution is highly practical.Comment: 31 pages. 6 figures. Preprint forma

Quantum Hacking: Experimental demonstration of time-shift attack against practical quantum key distribution systems

Quantum key distribution (QKD) systems can send signals over more than 100 km standard optical fiber and are widely believed to be secure. Here, we show experimentally for the first time a technologically feasible attack, namely the time-shift attack, against a commercial QKD system. Our result shows that, contrary to popular belief, an eavesdropper, Eve, has a non-negligible probability (~4%) to break the security of the system. Eve's success is due to the well-known detection efficiency loophole in the experimental testing of Bell inequalities. Therefore, the detection efficiency loophole plays a key role not only in fundamental physics, but also in technological applications such as QKD.Comment: 5 pages, 3 figures. Substantially revised versio