Optimal dynamic discrimination of similar [corrected] quantum systems in the presence of decoherence

Optimal dynamic discrimination (ODD) of a mixture of similar quantum systems with time series signals enables the extraction of the associated concentrations with reasonable levels of laser-pulse noise, signal detection errors, and imperfect signal detector resolution [Li et al., J. Chem. Phys. 122, 154103 (2005)]. The ODD paradigm is reexpressed in the density-matrix formulation to allow for the consideration of environmental decoherence on the quality of the extracted concentrations, along with the above listed factors. Simulations show that although starting in a thermally mixed state along with decoherence can be detrimental to discrimination, these effects can be counteracted by seeking a suitable optimal control pulse. Additional sampling of the temporal data also aids in extracting more information to better implement ODD.     

Time series evaluation of radiation portal monitor data for point source discrimination

Time series of data from radiation portal monitors are evaluated for radioactive sources by comparing background to vehicle spectra over time with a “spectral-distance” metric, isolating the contribution of anomalous radiation. This may diminish systematic fluctuations from vehicular background attenuation and allow time-shape filtering for discriminating compact sources. To examine this, a wavelet function similar in size to the expected source profile filters the spectral-distance output. Spectra from chosen isotopes are injected into data from a U.S. port of entry. The resulting data are analyzed with gross-counting, spectral-distance, and spatial algorithms. Combined spectral/spatial filtering is shown to enhance sensitivity and discrimination of compact versus distributed sources.     

Optimal quantum control with multi-polarization fields

The dynamical advantages for employing up to three independently shaped polarization fields are explored in the optimal control of quantum systems. The analysis compares multi-polarization optimal control with what may be achieved using linearly polarized (1-D) control. Simulations on model systems show how multi-polarization (2-D, 3-D) optimally shaped pulses can overcome symmetry forbidden transitions and improve control quality by better accessibility to the target state.     

Analysis of MALDI FT-ICR mass spectrometry data: A time series approach

Matrix-assisted laser desorption/ionization Fourier transform ion cyclotron resonance mass spectrometry is a technique for high mass-resolution analysis of substances that is rapidly gaining popularity as an analytic tool. Extracting signal from the background noise, however, poses significant challenges. In this article, we model the noise part of a spectrum as an autoregressive, moving average (ARMA) time series with innovations given by a generalized gamma distribution with varying scale parameter but constant shape parameter and exponent. This enables us to classify peaks found in actual spectra as either noise or signal using a reasonable criterion that outperforms a standard threshold criterion.     

Optical potentials in time dependent quantum systems: evaluation ofQ space probabilities

The time dependent extension of the Feshbach formalism allows the discussion of a set of nonunitary coupled channel equations in a given model space. We show how global and exclusive transition probabilities into states of the complementary space can be extracted from the solution of the model space problem.     

Statistical properties of signal entropy for use in detecting changes in time series data

Detecting changes in an underlying time series model for a system is an important task in many different fields, including econometrics, geophysics and process control. Specifically, in process control, detecting model changes is often the first step for fault detection, plant‐model mismatch assessment and data quality assessment for system identification. Signal entropy, which basically measures the amount of disorder in a given signal, can, not only segment a time series, but can also determine which regions have similar underlying models. Thus, the changes between the input and output signals can be used to determine when model is no longer an accurate representation of the system by comparing the current differential entropy against the historical differential entropy. This paper presents the statistical properties of signal entropy for discrete time systems. An example of the general results is provided by determining the entropy characteristics for first‐order systems driven by white noise. As well, a change detection index is proposed to assess changes in the time series model, which is tested on an experimental system. Copyright © 2013 John Wiley & Sons, Ltd.     

Effective potential analytic continuation calculations of real time quantum correlation functions: asymmetric systems

We apply the effective potential analytic continuation (EPAC) method to one-dimensional asymmetric potential systems to obtain the real time quantum correlation functions at various temperatures. Comparing the EPAC results with the exact results, we find that for an asymmetric anharmonic oscillator the EPAC results are in very good agreement with the exact ones at low temperature, while this agreement becomes worse as the temperature increases. We also show that the EPAC calculation for a certain type of asymmetric potentials can be reduced to that for the corresponding symmetric potentials.     

Joint statistical analysis of multichannel time series from single quantum dot-(Cy5)n constructs

One of the major challenges in single-molecule studies is how to extract reliable information from the inevitably noisy data. Here, we demonstrate the unique capabilities of multichannel joint statistical analysis of multispectral time series using F?ster resonance energy transfer (FRET) in single quantum dot (QD)-organic dye hybrids as a model system. The multispectral photon-by-photon registration allows model-free determination of intensity change points of the donor and acceptor channels independently. The subsequent joint analysis of these change points gives high-confidence assignments of acceptor photobleaching events despite the interference from background noise and from intermittent blinking of the QD donors and acceptors themselves. Finally, the excited-state lifetimes of donors and acceptors are calculated using the joint maximum likelihood estimation (MLE) method on the donor and acceptor decay profiles, guided by a four-state kinetics model.     

Study of simulation method of time evolution of atomic and molecular systems by quantum electrodynamics

We discuss a method to follow step‐by‐step time evolution of atomic and molecular systems based on quantum electrodynamics. Our strategy includes expanding the electron field operator by localized wavepackets to define creation and annihilation operators and following the time evolution using the equations of motion of the field operator in the Heisenberg picture. We first derive a time evolution equation for the excitation operator, the product of two creation or annihilation operators, which is necessary for constructing operators of physical quantities such as the electronic charge density operator. We, then, describe our approximation methods to obtain time differential equations of the electronic density matrix, which is defined as the expectation value of the excitation operator. By solving the equations numerically, we show “electron‐positron oscillations,” the fluctuations originated from virtual electron‐positron pair creations and annihilations, appear in the charge density of a hydrogen atom and molecule. We also show that the period of the electron‐positron oscillations becomes shorter by including the self‐energy process, in which the electron emits a photon and then absorbs it again, and it can be interpreted as the increase in the electron mass due to the self‐energy. © 2014 Wiley Periodicals, Inc.     

Optimal surface functionalization of silicon quantum dots

Surface functionalization is a critical step for Si nanocrystals being used as biological probes and sensors. Using density-functional tight-binding calculations, we systematically investigate the optical properties of silicon quantum dots (SiQDs) with various termination groups, including H, CH(3), NH(2), SH, and OH. Our calculations reveal that capping SiQDs with alkyl group (-Si-C-) induces minimal changes in the optical spectra, while covering the surface with NH(2), SH, and OH results in evident changes compared to hydrogenated SiQDs. The structural deformations and electronic property changes due to surface passivation were shown to be responsible for the above-described features. Interestingly, we find that the optical properties of SiQDs can be controlled by varying the S coverage on the surface. This tuning effect may have important implications in device fabrications.     

Monitoring dynamic systems with multiparameter fluorescence imaging

A new general strategy based on the use of multiparameter fluorescence detection (MFD) to register and quantitatively analyse fluorescence images is introduced. Multiparameter fluorescence imaging (MFDi) uses pulsed excitation, time-correlated single-photon counting and a special pixel clock to simultaneously monitor the changes in the eight-dimensional fluorescence information (fundamental anisotropy, fluorescence lifetime, fluorescence intensity, time, excitation spectrum, fluorescence spectrum, fluorescence quantum yield, distance between fluorophores) in real time. The three spatial coordinates are also stored. The most statistically efficient techniques known from single-molecule spectroscopy are used to estimate fluorescence parameters of interest for all pixels, not just for the regions of interest. Their statistical significance is judged from a stack of two-dimensional histograms. In this way, specific pixels can be selected for subsequent pixel-based subensemble analysis in order to improve the statistical accuracy of the parameters estimated. MFDi avoids the need for sequential measurements, because the registered data allow one to perform many analysis techniques, such as fluorescence-intensity distribution analysis (FIDA) and fluorescence correlation spectroscopy (FCS), in an off-line mode. The limitations of FCS for counting molecules and monitoring dynamics are discussed. To demonstrate the ability of our technique, we analysed two systems: (i) interactions of the fluorescent dye Rhodamine 110 inside and outside of a glutathione sepharose bead, and (ii) microtubule dynamics in live yeast cells of Schizosaccharomyces pombe using a fusion protein of Green Fluorescent Protein (GFP) with Minichromosome Altered Loss Protein 3 (Mal3), which is involved in the dynamic cycle of polymerising and depolymerising microtubules.     

Low variance energy estimators for systems of quantum Drude oscillators: treating harmonic path integrals with large separations of time scales

In the effort to develop atomistic models capable of accurately describing nanoscale systems with complex interfaces, it has become clear that simple treatments with rigid charge distributions and dispersion coefficients selected to generate bulk properties are insufficient to predict important physical properties. The quantum Drude oscillator model, a system of one-electron pseudoatoms whose "pseudoelectrons" are harmonically bound to their respective "pseudonuclei," is capable of treating many-body polarization and dispersion interactions in molecular systems on an equal footing due to the ability of the pseudoatoms to mimic the long-range interactions that characterize real materials. Using imaginary time path integration, the Drude oscillator model can, in principle, be solved in computer operation counts that scale linearly with the number of atoms in the system. In practice, however, standard expressions for the energy and pressure, including the commonly used virial estimator, have extremely large variances that require untenably long simulation times to generate converged averages. In this paper, low-variance estimators for the internal energy are derived, in which the large zero-point energy of the oscillators does not contribute to the variance. The new estimators are applicable to any system of harmonic oscillators coupled to one another (or to the environment) via an arbitrary set of anharmonic interactions. The variance of the new estimators is found to be much smaller than standard estimators in three example problems, a one-dimensional anharmonic oscillator and quantum Drude models of the xenon dimer and solid (fcc) xenon, respectively, yielding 2-3 orders of magnitude improvement in computational efficiency.     

Formation of dissipative structures upon homogenous oxidation of biosubstrata: Evaluation of dynamic characteristics and parameterization of time series

The possibility of formation of dissipative structures in the system consisting of biosubstrate and oxygenated iron (II) complexes is shown by the example of liquid-phase oxidation of cysteine. The results of evaluation of dynamic characteristics of the investigated processes (type of dynamics, dimensions of phase space and attractor, Lyapunov indicators, and the Kolmogorov-Sinai entropy) are given. Parameterization of the resulting time series was carried out using the approaches of flicker-noise spectroscopy.     

Resolution of strongly competitive product channels with optimal dynamic discrimination: application to flavins

Fundamental molecular selectivity limits are probed by exploiting laser-controlled quantum interferences for the creation of distinct spectral signatures in two flavin molecules, erstwhile nearly indistinguishable via steady-state methods. Optimal dynamic discrimination (ODD) uses optimally shaped laser fields to transiently amplify minute molecular variations that would otherwise go unnoticed with linear absorption and fluorescence techniques. ODD is experimentally demonstrated by combining an optimally shaped UV pump pulse with a time-delayed, fluorescence-depleting IR pulse for discrimination amongst riboflavin and flavin mononucleotide in aqueous solution, which are structurally and spectroscopically very similar. Closed-loop, adaptive pulse shaping discovers a set of UV pulses that induce disparate responses from the two flavins and allows for concomitant flavin discrimination of ～16σ. Additionally, attainment of ODD permits quantitative, analytical detection of the individual constituents in a flavin mixture. The successful implementation of ODD on quantum systems of such high complexity bodes well for the future development of the field and the use of ODD techniques in a variety of demanding practical applications.     

Alternative treatment of rotational quantum systems

The method of the Hill determinant proves to be useful in treating purely rotating quantum systems. The rotational Stark effect in symmetric-top molecules and the internal rotation in molecules are discussed as illustrative examples. The procedure can be used either to obtain the energy eigenvalues for a given model potential or to built it from experimental data.     

The utilization of chemical shift and spin-lattice (T1) relaxation time data for the discrimination of isomeric indenoisoxazoles

Treatment of 2-pivaloyl-1,3-indandione with hydroxylamine leads to the formation of a pair of isomeric indenoisoxazoles, the product formed dependent upon the cyclization conditions. Under acidic conditions, 8-t-butylindeno[1,2-c]isoxazol-7-one ( 5 ) is formed while under neutral or basic conditions, an oxime, 2 , is generated which may then be cyclized under acidic conditions to give 3-t-butylindeno[1,2-c]isoxazol-4-one ( 4 ). Although these isomeric indenoisoxazoles may be discriminated by chemical means, we were interested in developing an unequivocal method for distinguishing these and potentially other isomeric pairs by spectroscopic means. A ¹³C-nmr based method for the discrimination of these isomers which is based on the utilization of chemical shift arguments and spin-lattice relaxation data is thus presented.     

系列烷基苯磺酸盐对烷烃的动态界面性能研究

从表面活性剂分子量、表面活性剂浓度、电解质浓度、 烷烃碳数等方面考察了系列烷基苯磺酸盐异构体纯化合物的油水动态界面张力行为。研究表明,表面活性剂分子量越大和电解质浓度增加使界面张力动态变化越慢,达到平衡所需时间越长;表面活性剂浓度增加和烷烃碳数增加使界面张力动态变化加快,达到平衡所需时间减少。     

A new time evolving Gaussian series representation of the imaginary time propagator

Frantsuzov and Mandelshtam [J. Chem. Phys. 121, 9247 (2004)] have recently demonstrated that a time evolving Gaussian approximation (TEGA) to the imaginary time propagator exp(-betaH) is useful for numerical computations of anharmonically coupled systems with many degrees of freedom. In this paper we derive a new exact series representation for the imaginary time propagator whose leading order term is the TEGA. One can thus use the TEGA not only as an approximation but also to obtain the exact imaginary time propagator. We also show how the TEGA may be generalized to provide a family of TEGA's. Finally, we find that the equations of motion governing the evolution of the center and width of the Gaussian may be thought of as introducing a quantum friction term to the classical evolution equations.