Noise-induced dynamics in a delayed bistable system with correlated noises

The resonance behaviors, such as coherence resonance and stochastic resonance, are studied in a delayed bistable system subject to correlated noises and a weak harmonic excitation. For weak noise intensities and small feedback gains, the analytic expressions of output spectrum and linear spectrum amplification are derived based on the theory proposed by Tsimring [14] [L.S. Tsimring, A. Pikovsky, Noise-induced dynamics in bistable systems with delay, Phys. Rev. Lett. 87 (2001) 250602]. The results show that the peak in the output spectrum at the frequency corresponding to the time delay attains the maximum for an intermediate amount of noise intensity and the coherence resonance appears. The correlation between noises can induce the suppression and the stochastic resonance in the curve of spectrum amplification, which is absent for the case of uncorrelated additive and multiplicative noises. Moreover, the system also exhibits the frequency stochastic resonance.     

Deformed dispersion relations and the degree of the coherence function

The analysis of the modifications that the presence of a deformed dispersion relation entails in the roots of the so-called degree of coherence function, for a beam embodying two different frequencies and moving in a Michelson interferometer, is carried out. The conditions to be satisfied, in order to detect this kind of quantum gravity effect, are also obtained.     

SLD光谱调制对光纤陀螺性能的影响

对光纤陀螺中SLD光谱调制度的变化进行了实验研究.从理论上阐述了光路系统中光谱的调制度增大的原因，其仿真与实验结果非常一致.在此基础上，进一步分析了光谱调制度对相干函数的影响，评估了二阶相干峰引起的光纤陀螺误差水平.     

Coherent spaces,Boolean rings and quantum gates

Coherent spaces spanned by a finite number of coherent states, are introduced. Their coherence properties are studied, using the Dirac contour representation. It is shown that the corresponding projectors resolve the identity, and that they transform into projectors of the same type, under displacement transformations, and also under time evolution. The set of these spaces, with the logical OR and AND operations is a distributive lattice, and with the logical XOR and AND operations is a Boolean ring (Stone’s formalism). Applications of this Boolean ring into classical CNOT gates with n$n$-ary variables, and also quantum CNOT gates with coherent states, are discussed.     

PFT—NMR相位循环的计算机辅助设计

本文介绍了通过选择相干传递路径来计算相位循环的理论依据。在此基础上提出了一个计算机程序PHASE.BAS用于计算相位循环。使用此程序设计了一个128步的相循环用于一维和二维INADEQUATE实验。实验结果表明此相循环能很好地消除单量子信号、压制t_1噪声,其效果明显优于Bruker MSL脉冲序列库中的32次循环的结果。     

Linear phase slope in pulse design: application to coherence transfer

Using optimal control methods, robust broadband excitation pulses can be designed with a defined linear phase dispersion. Applications include increased bandwidth for a given pulse length compared to equivalent pulses requiring no phase correction, selective pulses, and pulses that mitigate the effects of relaxation. This also makes it possible to create pulses that are equivalent to ideal hard pulses followed by an effective evolution period. For example, in applications, where the excitation pulse is followed by a constant delay, e.g. for the evolution of heteronuclear couplings, part of the pulse duration can be absorbed in existing delays, significantly reducing the time overhead of long, highly robust pulses. We refer to the class of such excitation pulses with a defined linear phase dispersion as ICEBERG pulses (Inherent Coherence Evolution optimized Broadband Excitation Resulting in constant phase Gradients). A systematic study of the dependence of the excitation efficiency on the phase dispersion of the excitation pulses is presented, which reveals surprising opportunities for improved pulse sequence performance.     

Single or triple gradients?

Pulsed Field Gradients (PFGs) have become ubiquitous tools not only for Magnetic Resonance Imaging (MRI), but also for NMR experiments designed to study translational diffusion, for spatial encoding in ultra-fast spectroscopy, for the selection of desirable coherence transfer pathways, for the suppression of solvent signals, and for the elimination of zero-quantum coherences. Some of these experiments can only be carried out if three orthogonal gradients are available, while others can also be implemented using a single gradient, albeit at some expense of performance. This paper discusses some of the advantages of triple- with respect to single-gradient probes. By way of examples we discuss (i) the measurement of small diffusion coefficients making use of the long spin-lattice relaxation times of nuclei with low gyromagnetic ratios gamma such as nitrogen-15, and (ii) the elimination of zero-quantum coherences in Exchange or Nuclear Overhauser Spectroscopy (EXSY or NOESY) experiments, as well as in methods relying on long-lived (singlet) states to study very slow exchange or diffusion processes.     

Spin density wave dislocation in chromium probed by coherent X-ray diffraction

We report on the study of a magnetic dislocation in pure chromium. Coherent X-ray diffraction profiles obtained on the incommensurate Spin Density Wave (SDW) reflection are consistent with the presence of a dislocation of the magnetic order, embedded at a few micrometers from the surface of the sample. Beyond the specific case of magnetic dislocations in chromium, this work may open up a new method for the study of magnetic defects embedded in the bulk.