Coherence destruction

The ability to create and observe coherent dynamics in heterostructures offers the intriguing possibility to control the dynamics of the charge carriers. Recent experiments have shown that control in such systems is indeed possible. For example, phase-locked laser pulses can be used to coherently amplify or suppress THz radiation in a coupled quantum well [5]. The direction of a photocurrent can be controlled by exciting a structure with a laser field and its second harmonic, and then varying the phase difference between the two fields [8,9]. Phase-locked pulses tuned to excitonic resonances allow population control and coherent destruction of heavy hole wave packets [10]. Complex filters can be designed to enhance specific characteristics of the THz emission [11,12]. These experiments are impressive demonstrations of the ability to control the microscopic and macroscopic dynamics of solid-state systems. 

In general, coherence destruction is due to elastic collisions, depopulation, or scattering by phonons. However, the dephasing in the context of wavepackets is not due to such collision, scattering, or depopulation processes but can be explained as follows. Transfer of a part of the wavepacket takes place at different positions near the crossing point of two potential curves 1 and 2 (Fig. 3). Since the speed of the... 

Unlike the previous section, however, these pulses are used to return solvent (most often water) resonances back to the +Z-axis without the need for selection or coherence destruction, effectively removing much of the echo refocusing, radiation damping, demagnetization, and alternate suppression concerns. 

The phenomenon of coherent destruction of tunneling (CDT) was first discovered by Grossmann et al. [16, 48-51], They considered a particle moving in a onedimensional quartic double-well potential driven by a monochromatic laser field and showed numerically that for specific values of the frequency and amplitude of the radiation, the particle is forced to stay in one of the two wells as long as the laser field is on. Since then, this intriguing phenomenon has been the object of further theoretical analysis [17, 18, 52-58], extended in various forms [20, 59-70], and demonstrated experimentally in different physical systems [71-74]. The role of CDT in processes such as the strong field ionization of diatomic molecules [75] or the proton transfer dynamics in tropolone [76] has also been discussed. 

The phenomenon of coherent destruction of tunneling was investigated in a six dimensional, rotationless model of NHD2. Two different regimes were considered for the... 

M. Sala, F. Gatti and S. Guerin, Coherent destruction of tunneling in a six-dimensional model of NHD2 a computational study using the multi-configuration time-dependent Hartree method , J. Chem. Phys. 141, 164326 (2014)... 

The simplest scheme that accounts for the destruction of phase coherence is the so-called stochastic interruption model [Nikitin and Korst 1965 Simonius 1978 Silbey and Harris 1989]. Suppose the process of free tunneling is interrupted by a sequence of collisions separated by time periods vo = to do After each collision the system forgets its initial phase, i.e., the off-diagonal matrix elements of the density matrix p go to zero, resulting in the density matrix p ... 

The treatment of section 2.3 concerned with the destruction of coherence by the environment applies to this case. 

The modulus of 7i2(t) gives a measure of the coherence ranging from incoherent (0) to coherent (1) its phase determines whether interference is constructive or destructive. 

The prerequisite for an experimental test of a molecular model by quasi-elastic neutron scattering is the calculation of the dynamic structure factors resulting from it. As outlined in Section 2 two different correlation functions may be determined by means of neutron scattering. In the case of coherent scattering, all partial waves emanating from different scattering centers are capable of interference the Fourier transform of the pair-correlation function is measured Eq. (4a). In contrast, incoherent scattering, where the interferences from partial waves of different scatterers are destructive, measures the self-correlation function [Eq. (4b)]. 

Coherence Microscopy. A technology for rapid, in vivo, non-destructive visualization of plant and plant cells. Plant Physiology 123 3-15. 

Hittinger, J.W., Mattozzi, M., Myers, W.R., Williams, M.E., Reeves, A., Parsons, R.L., Haskell, R.C., Petersen, D.C., Wang, R. and Medford, J.I. (2000). Optical Coherence Microscopy A technology for rapid in vivo, non-destructive visualization of plant and plant cells. Plant Physiology 123 3-15. 

Fig. 3.10. Schematics of interferences of coherent phonons in double-pump experiments. (a) constructive interference in ISRS mechanism. Bold grey arrows indicate the first and the second ISRS driving forces, (b) constructive interferences in DECP mechanism, (c) destructive interferences in DECP mechanism...

Foucault, like his French predecessor and mentor, Gaston Bachelard, paid particular attention to the primacy in history of discursive breaks and ruptures in knowledge or belief systems.3 In this and in Foucault s emphasis on the relative coercion that disciplines exercised on their practitioners, he made arguments already familiar to Anglo-American scholars acquainted with Kuhn s characterizations of "normal science" and the reasons for a scientific community s coherent outlook. However, unlike Kuhn, Foucault declined to dissect the so-called hard sciences as objects of inquiry, restricting himself to discourses and power relationships in the medical, biological, and social sciences.4 However, Foucault did see the potential in the application of his method for the destruction of the demarcation between scientific and nonscientific spheres of action and belief. 

The diffraction of visible light (with a wavelength X in the range 350 to 700 nm) by small holes, slits or lattices is a well-known phenomenon which results from destructive and constructive interferences of coherent waves. For a lattice, diffraction may occur when the wavelength is lower than the lattice repeat distances. 

As discussed by M. Shapiro and R Brumer in the book Quantum Control of Molecular Processes, there are two general control strategies that can be applied to harness and direct molecular dynamics optimal control and coherent control. The optimal control schemes aim to find a sef of external field parameters that conspire - through quantum interferences or by incoherent addition - to yield the best possible outcome for a specific, desired evolution of a quantum system. Coherent control relies on interferences, constructive or destructive, that prohibit or enhance certain reaction pathways. Both of these control strategies meet with challenges when applied to molecular collisions. 

The method is based on the fact that one can excite coherently a set of overlapping resonances such that their decay exhibits a steplike behavior the system starts in a quiescent period in which no spontaneous emission occurs, followed by a photon burst in which spontaneous emission is greatly accelerated, followed by another quiescent period, and so on. The quiescent period (and subsequent photon bursts) is due to destructive and constructive interferences between the overlapping resonances. The reason it is impossible to suppress the decay over all times in this... 

A further effect is discussed in Chapter 5, namely that of spin-orbit scattering. This effect preserves the coherence of the two scattered waves but changes the constructive interference into a destructive one. The characteristic time tw is believed to be independent of Ty and inversely proportional to Z4, where Z is the atomic number. An analysis by Fukuyama and Hoshino (1981) shows that Ac depends on and leads to a behaviour as shown in Fig. 1.24. The negative part should be observed only for heavy metals. 

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