Destroying coherence

As argued in section 2.3, when the asymmetry e far exceeds A, phonons should easily destroy coherence, and relaxation should persist even in the tunneling regime. Such an incoherent tunneling, characterized by a rate constant, requires a change in the quantum numbers of the vibrations coupled to the reaction coordinate. In section 2.3 we derived the expression for the intradoublet relaxation rate with the assumption that only the one-phonon processes are relevant. 

We thus see that the purely magnetic evolution (4.11) of the polarization moment is, in essence, a linear change in time of its phase ip according to (4.12), with conservation of the module Mod pq (circle in Fig. 4.1(c)). The factor e1 means that the dependence pq (t) is periodic with a period Tq = 2ir/Qu)ji, i.e. that each transversal component of a polarization moment passes into itself with its own frequency Quj>. This is in full agreement with what has been said before in Section 2.3 on the connection between the coherence and symmetry of p(6,ip). The model presented affords the conservation of the shape of the angular momenta distribution p(0,ip) in the course of precession (see Fig. 4.1(6)). Incidentally, it may not seem quite appropriate in this context to maintain the statement that the magnetic field itself destroys coherency , as described by the transversal components pq, Q 0. Indeed, it follows from (4.11) that at... 

Note that disorder, which was neglected above, is also able to destroy coherent superradiant emission of ID and 2D polaritons. This can happen when the uncertainty of the exciton wavevector arising due to scattering of an exciton by disorder will be of the order of value Eexc/hc. A quantitative theory of this effect has been developed in the paper by Orrit et al. (23). 

Radio astronomy was discovered at 20 MHz, but the quest for higher angular resolution with the single-dish telescopes then available, led quickly to most observations being conducted at higher frequencies. Interferometers were constructed to operate at frequencies below 100 MHz, but they had short baselines (<5 km). Short baselines were motivated by the belief that ionospherically induced phase fluctuations would destroy coherence on longer baselines. 

M continually decreases under the influence of spin-spin relaxation which destroys the initial phase coherence of the spin motion within they z-plane. In solid-state TREPR, where large inliomogeneous EPR linewidths due to anisotropic magnetic interactions persist, the long-time behaviour of the spectrometer output, S(t), is given by... 

Aside from merely calculational difficulties, the existence of a low-temperature rate-constant limit poses a conceptual problem. In fact, one may question the actual meaning of the rate constant at r = 0, when the TST conditions listed above are not fulfilled. If the potential has a double-well shape, then quantum mechanics predicts coherent oscillations of probability between the wells, rather than the exponential decay towards equilibrium. These oscillations are associated with tunneling splitting measured spectroscopically, not with a chemical conversion. Therefore, a simple one-dimensional system has no rate constant at T = 0, unless it is a metastable potential without a bound final state. In practice, however, there are exchange chemical reactions, characterized by symmetric, or nearly symmetric double-well potentials, in which the rate constant is measured. To account for this, one has to admit the existence of some external mechanism whose role is to destroy the phase coherence. It is here that the need to introduce a heat bath arises. 

Static defects scatter elastically the charge carriers. Electrons do not loose memory of the phase contained in their wave function and thus propagate through the sample in a coherent way. By contrast, electron-phonon or electron-electron collisions are inelastic and generally destroy the phase coherence. The resulting inelastic mean free path, Li , which is the distance that an electron travels between two inelastic collisions, is generally equal to the phase coherence length, the distance that an electron travels before its initial phase is destroyed ... 

To sum up, the Kurizki-Shapiro-Brumer photocurrent coherent control exhibits resilience to noise and fluctuations. Nevertheless, excessive noise will degrade or completely destroy the effect. We therefore turn to noise/fluctuation control in what follows. 

R. D. Levine The coherence that is being discussed by Profs. Troe and Zewail is due to a localized vibrational motion in the AB diatomic product of a photodissociation experiment ABC — AB + C. Such experiments have been done both for the isolated ABC molecule and for the molecule in an environment. As the fragments recede, effective coupling of the AB vibrational motion to the other degrees of freedom can rapidly destroy the localized nature of the vibrational excitation. 

In any case, crystal lattices are destroyed by the field-driven decomposition. If the original AX/AY interface remains coherent, stresses develop which will consume some driving force. In other words, the AX/AY interface is then polarized. A determination of the amount (=jA/A-dt) of decomposed AX(AY) at the interface should give a very sensitive method to measure extremely small differences in the elec-... 

In a further operation, these stresses can be eliminated by introducing an array of dislocations in the interface as in Fig. B.7c. The resulting interface consists of patches of coherent interface separated by dislocations. The cuts and displacements necessary to introduce the dislocations destroy the overall coherence of the interface, which is therefore considered to be semicoherent with respect to the reference... 

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