Sensitivity and specificity of coherence and phase synchronization analysis

In this Letter, we show that coherence and phase synchronization analysis are sensitive but not specific in detecting the correct class of underlying dynamics. We propose procedures to increase specificity and demonstrate the power of the approach by application to paradigmatic dynamic model systems.     

Suppression of electron spin-echo envelope modulation peaks in double quantum coherence electron spin resonance

We show the use of the observer blind spots effect for the elimination of electron spin-echo envelope modulation (ESEEM) peaks in double quantum coherence (DQC) electron spin resonance (ESR). The suppression of ESEEM facilitates the routine and unambiguous extraction of distances from DQC-ESR spectra. This is also the first demonstration of this challenging methodology on commercial instrumentation.     

Sensitivity gain by simultaneous acquisition of two coherence pathways: the HNCA(+) experiment

In most multidimensional nuclear magnetic resonance experiments a single and distinct coherence transfer pathway is selected by phase cycling or by pulsed field gradients. It was shown that simultaneously exploiting more than one coherence transfer pathway could increase the overall sensitivity of NMR experiments. However, sensitivity enhancement schemes described to date introduce additional delays in the pulse schemes, resulting in considerable decrease of the expected sensitivity gain when applied to biomolecules due their fast transverse relaxation. A novel sensitivity enhancement principle which increases sensitivity of an experiment by simultaneously exploiting two completely independent coherence pathways in a single NMR pulse scheme is presented in this paper. As an example an improved HNCA experiment, the HNCA(+), is presented, which combines the "out-and-back" coherence transfer pathway used in HNCA with an "out-and-stay" experiment, analogous to HCANH, without adding any time periods compared to the conventional HNCA pulse sequence. The applicability of the HNCA(+) was theoretically evaluated with regard to different sizes of peptides or proteins, which showed that the experimental time can be reduced twofold in ideal cases. The application of this novel experiment to a 7-kDa protein showed a 20% sensitivity gain of HNCA(+) when compared to conventional HNCA.     

Interference due to coherence swapping

We propose a method called ‘coherence swapping’ which enables us to create superposition of a particle in two distinct paths, which is fed with initially incoherent, independent radiation. This phenomenon is also present for the charged particles, and can be used to swap the effect of flux line due to the Aharonov-Bohm effect. We propose an optical version of experimental set-up to test the coherence swapping. The phenomenon, which is simpler than entanglement swapping or teleportation, raises some fundamental questions about the true nature of wave-particle duality, and also opens up the possibility of studying the quantum erasure from a new angle.     

Average coherence with respect to complementary measurements

We investigate the average coherence with respect to a complete set of complementary measurements.By using a Wigner-Yanase skew information-based coherence measure introduced in Luo and Sun(2017 Phys.Rev.A 96,022130),we evaluate the average coherence of a state with respect to any complete set of mutually unbiased measurements and general symmetric informationally complete measurements,respectively.We also establish analytically the relations among these average coherences.     

从迈克耳孙干涉仪到光学相干层析术

介绍了迈克耳孙干涉仪在物理学发展史上的重要作用及生物医学成像技术的发展状况．从迈克耳孙干涉仪的发展过程出发,讨论了光学相干层析术的原理、特性及其在生物医学成像、物理学、材料科学中的应用,并将频谱光学相干层析术与傅里叶变换光谱术作了比较,最后讨论了它在教学上的意义．     

Sensitivity to amplitude-modulated vibrotactile signals

Temporal modulation transfer functions were measured for sinusoidally amplitude-modulated vibratory stimuli delivered to the thenar eminence of the hand. Results for sinusoidal carriers at 25, 50, 100, and 250 Hz reflected greater sensitivity to modulation than those for either broadband or narrow-band noise carriers. The correspondence of these results to other measures of temporal sensitivity in the tactile system was examined. In addition, findings are discussed in view of their relevance to comparisons across sensory modalities, and to the design of vibrotactile aids for hearing-impaired persons.     

Segregation of concurrent sounds. II: Effects of spectral envelope tracing, frequency modulation coherence, and frequency modulation width

The research presented here concerns the simultaneous grouping of the components of a vocal sound source. McAdams [J. Acoust. Soc. Am. 86, 2148-2159 (1989)] found that when three simultaneous vowels at different pitches were presented with subaudio frequency modulation, subjects judged them as being more prominent than when no vibrato was present. In a normal voice, when the harmonics of a vowel undergo frequency modulation they also undergo an amplitude modulation that traces the spectral envelope. Hypothetically, this spectral tracing could be one of the criteria used by the ear to group components of each vowel, which may help explain the lack of effect of frequency modulation coherence among different vowels in the previous study. In this experiment, two types of vowel synthesis were used in which the component amplitudes of each vowel either remained constant with frequency modulation or traced the spectral envelope. The stimuli for the experiment were chords of three different vowels at pitch intervals of five semitones (ratio 1.33). All the vowels of a given stimulus were produced by the same synthesis method. The subjects' task involved rating the prominence of each vowel in the stimulus. It was assumed that subjects would judge this prominence to be lower when they were not able to distinguish the vowel from the background sound. Also included as stimulus parameters were the different permutations of the three vowels at three pitches and a number of modulation conditions in which vowels were unmodulated, modulated alone, and modulated either coherently with, or independently of, the other vowels. Spectral tracing did not result in increased ratings of vowel prominence compared to stimuli where no spectral tracing was present. It would therefore seem that it has no effect on grouping components of sound sources. Modulated vowels received higher prominence ratings than unmodulated vowels. Vowels modulated alone were judged to be more prominent than vowels modulated with other vowels. There was, however, no significant difference between coherent and independent modulation of the three vowels. Differences among modulation conditions were more marked when the modulation width was 6% than when it was 3%.     

Symmetry approach to coherence in spontaneous nuclear decay

We apply the symmetry approach of coherence in spontaneous radiation processes to nuclear electromagnetic decays. Wavelength limits on the cooperation number are addressed. Basic characteristics of nuclear enhanced spontaneous decay in the absence of stimulated emission are described.     

A realistic experiment to demonstrate macroscopic quantum coherence

According to quantum theory, microscopic objects exist in a superposition of distinct states until they are “observed”. Nobody knows whether such quantum coherence can actually exist in a macroscopic system. In the experiment described here, a superconducting quantum interference device is extremely well isolated from any interaction with internal or external modes, and a superposition state can be demonstrated even if it lasts for less than 1 ns. This is accomplished by using superconducting digital electronic circuitry as the experimental apparatus. If successful, it is the first step toward a future full-scale quantum computer fabricated using integrated circuit manufacturing techniques.     

原子相干性的研究进展

原子相干效应是相干电磁场与原子相互作用的产物,在量子光学领域有重要的研究价值.许多重要的物理现象都是由原子相干效应引起的.文章介绍了基于原子相干效应的电磁感应光透明、相干烧孔、双暗态、真空感应相干、部分受激拉曼绝热过程的光存储、光信息在不同通道之间的转换与擦除等现象的理论和实验研究,并简单介绍了它们的应用价值.     

量子相干

量子相干不仅是量子力学中的一个基本概念,同时也是重要的量子信息处理的物理资源.随着基于资源理论框架的量子相干度量方案的提出,量子相干度的量化研究成为近年来人们关注的一个热点问题.量子相干作为一种物理资源也十分脆弱,极容易受到环境噪声的影响而产生退相干,因此开放系统中的量子相干演化和保持也是人们广泛关注的课题.另外,量子相干在量子多体系统、量子热动力学、量子生物学等领域也有着潜在的应用价值.本文介绍量子相干度量的资源理论框架和基于该框架定义的相对熵相干性、l1范数相干性、基于量子纠缠的相干性、基于凸顶结构的相干性和相干鲁棒性等量子相干度量函数,概述开放系统中量子相干演化的动力学行为、典型信道的量子相干产生和破坏能力以及量子相干的冻结等现象,同时例举量子相干在Deutsch-Jozsa算法、Grover算法以及量子多体系统相变问题研究等方面的重要应用.量子相干研究仍处于快速发展之中,期望本综述能为该领域的发展带来启示.     

原子相干性的研究进展

原子相干效应是相干电磁场与原子相互作用的产物,在量子光学领域有重要的研究价值.许多重要的物理现象都是由原子相干效应引起的.文章介绍了基于原子相干效应的电磁感应光透明、相干烧孔、双暗态、真空感应相干、部分受激拉曼绝热过程的光存储、光信息在不同通道之间的转换与擦除等现象的理论和实验研究,并简单介绍了它们的应用价值.     

An intrinsic limit to quantum coherence due to spontaneous symmetry breaking

We investigate the influence of spontaneous symmetry breaking on the decoherence of a many-particle quantum system. This decoherence process is analyzed in an exactly solvable model system that is known to be representative of symmetry broken macroscopic systems in equilibrium. It is shown that spontaneous symmetry breaking imposes a fundamental limit to the time that a system can stay quantum coherent. This universal time scale is t(spon) approximately = 2piNH/(kBT), given in terms of the number of microscopic degrees of freedom N, temperature T, and the constants of Planck (h) and Boltzmann (kB).     

Robust decoupling techniques to extend quantum coherence in diamond

We experimentally demonstrate over 2 orders of magnitude increase in the room-temperature coherence time of nitrogen-vacancy centers in diamond by implementing decoupling techniques. We show that equal pulse spacing decoupling performs just as well as nonperiodic Uhrig decoupling and also allows us to take advantage of revivals in the echo to explore the longest coherence times. At short times, we can extend the coherence of particular quantum states out from T2*=2.7 μs out to an effective T2>340 μs. For preserving arbitrary states we show the experimental importance of using pulse sequences that compensate the imperfections of individual pulses for all input states through judicious choice of the phase of the pulses. We use these compensated sequences to enhance the echo revivals and show a coherence time of over 1.6 ms in ultrapure natural abundance 13C diamond.     

Spectral modulation masking patterns reveal tuning to spectral envelope frequency

Auditory processing appears to include a series of domain-specific filtering operations that include tuning in the audio-frequency domain, followed by tuning in the temporal modulation domain, and perhaps tuning in the spectral modulation domain. To explore the possibility of tuning in the spectral modulation domain, a masking experiment was designed to measure masking patterns in the spectral modulation domain. Spectral modulation transfer functions (SMTFs) were measured for modulation frequencies from 0.25 to 14 cycles/octave superimposed on noise carriers either one octave (800-1600 Hz, 6400-12,800 Hz) or six octaves wide (200-12,800 Hz). The resulting SMTFs showed maximum sensitivity to modulation between 1 and 3 cycles/octave with reduced sensitivity above and below this region. Masked spectral modulation detection thresholds were measured for masker modulation frequencies of 1, 3, and 5 cycles/octave with a fixed modulation depth of 15 dB. The masking patterns obtained for each masker frequency and carrier band revealed tuning (maximum masking) near the masker frequency, which is consistent with the theory that spectral envelope perception is governed by a series of spectral modulation channels tuned to different spectral modulation frequencies.