Quantum interference effect

In the presence of weak disorder, one should consider an additional contribution to the resistivity due to weak localisation resulting from quantum interference effects and/or that due to Coulomb interaction effects. A single-carrier weak localisation effect is produced by constructive quantum interference between elastically back-scattered partial-carrier-waves, while disorder attenuates the screening between charge carriers, thus increasing their Coulomb interaction. So, both effects are enhanced in the presence of weak disorder, or, in other words, by defect scattering. This was previously discussed for the case of carbons and graphites [7]. 

As shown above, experiments on individual MWCNTs allowed to illustrate a variety of new electrical properties on these materials, including 2D quantum interference effects due to weak localisation and UCFs. However, owing to the relatively large diameters of the concentric shells, no ID quantum effects have been observed. In addition, experimental results obtained on MWCNTs were found difficult to interpret in a quantitative way due to simultaneous contributions of concentric CNTs with different diameters and chiralities. 

Stafford CA, Cardamone DM, Mazumdar S (2007) The quantum interference effect transistor. Nanotechnology 18(42) 424014... 

Sivco, and Alfred Y. Cho, Quantum Interference Effects in Intersubband Transitions H. C. Liu, Quantum Well Infrared Photodetector Physics and Novel Devices S. D. Gunapala and S. V. Bandara, Quantum Well Infrared Photodetector (QWIP) Focal Plane Arrays... 

In previous papers [10,11] we have formulated a procedure for splitting the ground-state energy of a multifermionic system into an averaged, structure-less part, E, and a residual, shell-structure part, 8E. The latter originates from quantum interference effects of the one-particle motion in the confining potential [12] and has the form of a shell-correction expansion 5E = It was also shown [11] that the first-order corrective term,... 

In NaxW03-yFy Doumerc (1978) observed a transition that has all the characteristics of an Anderson transition similar phenomena are observed in NaxTayW3 y03. The results are shown in Fig. 7.14. It is unlikely that this transition is generated by the overlap of two Hubbard bands with tails (Chapter 1, Section 4) this could only occur if it took place in an uncompensated alkali-metal impurity band, which seems inconsistent with the comparatively small electron mass. We think rather that in the tungsten (or tungsten-tantalum) 5d-band an Anderson transition caused by the random positions of Na (and F or Ta) atoms occurs. The apparent occurrence of amiD must, as explained elsewhere, indicate that a at the temperature of the experiments. Work below 100 K, to look for quantum interference effects, does not seem to have been carried out. 

Most amorphous metallic alloys do not show a metal-insulator transition. They do, however, show moderate changes in the resistivity with temperature, some of which can be interpreted in terms of the quantum interference effect, together with the interaction effect of Altshuler and Aronov (Chapter 5, Section 6). These will be described below. Amorphous alloys of the form Nb Six Au Six etc. do, however, show a metal-insulator transition of Anderson type, and some of those are treated in Chapter 1, Section 7. 

The other comment I would like to make is that the positive value of the 0 parameter you observe is due to a quantum interference effect. A simple mixing of the ground state with the excited state in the final continuum state hardly affects the directional properties of the dipole matrix elements per se because the transition dipole matrix elements between different states within the ground state are very small. Namely, if... 

Two lines of inquiry will be important in future work in photochemistry. First, both the traditional and the new methods for studying photochemical processes will continue to be used to obtain information about the subtle ways in which the character of the excited state and the molecular dynamics defines the course of a reaction. Second, there will be extension and elaboration of recent work that has provided a first stage in the development of methods to control, at the level of the molecular dynamics, the ratio of products formed in a branching chemical reaction. These control methods are based on exploitation of quantum interference effects. One scheme achieves control over the ratio of products by manipulating the phase difference between two excitation pathways between the same initial and final states. Another scheme achieves control over the ratio of products by manipulating the time interval between two pulses that connect various states of the molecule. These schemes are special cases of a general methodology that determines the pulse duration and spectral content that maximizes the yield of a desired product. Experimental verifications of the first two schemes mentioned have been reported. Consequently, it is appropriate to state that control of quantum many-body dynamics is both in principle possible and is... 

The research of Paul Brumer and his colleagues addresses several fundamental problems in theoretical chemical physics. These include studies of the control of molecular dynamics with lasers.98 In particular, the group has demonstrated that quantum interference effects can be used to control the motion of molecules, opening up a vast new area of research. For example, one can alter the rate and yield of production of desirable molecules in chemical reactions, alter the direction of motion of electrons in semiconductors, and change the refractive indices of materials etc. by creating and manipulating quantum interferences. In essence, this approach, called coherent control, provides a method for manipulating chemistry at its most fundamental level.99... 

The behaviour of the quantum oscillations in (BEDO-TTF)5[CsHg(SCN)4]2 seems to be in good agreement with the predictions of tight binding band structure calculations. The additional frequencies in the SdH oscillations spectrum are most probably caused by the quantum interference effect. Thus, we propose that Fig. 5 provides an adequate description of the Fermi surface of (BEDO-TTF)5[CsHg(SCN)4]2 and that the... 

Stark R.W. and Reifenberg R. (1977) Quantitative Theory of Quantum Interference Effect./. Low Temp. Phys. 26,763. 

Control of the type discussed above, in which quantum interference effects are used to constructively or destructively alter product properties, is called coherent control (CC). Photodissociation of a superposition state, the scenario described above, will be seen to be just one particular implementation of a general principle of coherent control Coherently driving a state with phase coherence through multiple, coherent,... 

The optimization procedure yields a set of coefficients a,-. Of considerable interiasff is the question of whether these coefficients merely define a new vector that is simply a vector in a rotated coordinate system. If so, this would indicate that the optimqifl solution corresponds to a simple classical reorientation of the di atomic-moleciilee angular momentum vector. Examination of the optimal results [238] indicate " this is not the case. That is, control is the result of quantum interference effects ... 

Although not immediately obvious, this control scenario relies entirely t quantum interference effects. To see this note that in the absence of an pulse, excitation from D) or L) to level E ), for example, occurs via one excitation with e,(t), i = 1,2. In this case, as noted above, there is no chiral.c By contrast, with nonzero e0(t), there is an additional (interfering) route to ] is, a two-photon route using j(t) excitation to level Ej),j A i, followed by i... 

All of the quantum control scenarios involve a host of laser and system parameters. To obtain maximal control in any scenario necessitates a means of tuning the system and laser parameters to optimally achieve the desired objective. This topic, optimal control, is introduced and discussed in Chapters 4 and 13. The role of quantum interference effects in optimal control are discussed as well, providing a uniform picture of control via optimal pulse shaping and coherent control. 

Recent years have also witnessed exciting developments in the active control of unimolecular reactions [30,31]. Reactants can be prepared and their evolution interfered with on very short time scales, and coherent hght sources can be used to imprint information on molecular systems so as to produce more or less of specified products. Because a well-controlled unimolecular reaction is highly nonstatistical and presents an excellent example in which any statistical theory of the reaction dynamics would terribly fail, it is instmctive to comment on how to view the vast control possibihties, on the one hand, and various statistical theories of reaction rate, on the other hand. Note first that a controlled unimolecular reaction, most often subject to one or more external fields and manipulated within a very short time scale, undergoes nonequilibrium processes and is therefore not expected to be describable by any unimolecular reaction rate theory that assumes the existence of an equilibrium distribution of the internal energy of the molecule. Second, strong deviations Ifom statistical behavior in an uncontrolled unimolecular reaction can imply the existence of order in chaos and thus more possibilities for inexpensive active control of product formation. Third, most control scenarios rely on quantum interference effects that are neglected in classical reaction rate theory. Clearly, then, studies of controlled reaction dynamics and studies of statistical reaction rate theory complement each other. 

Equation (369) indicates that to obtain the semiclassical reaction rate constant k T) one needs to carry out the multidimensional phase-space average for a sufficiently long time. This is far from trivial, since the integrand in Eq. (369) is highly oscillatory due to quantum interference effects between the sampling classical trajectories. The use of some filtering methods to dampen the oscillations in the integrand may improve the accuracy of the semiclassical calculation. 

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