Coherent control strategies

In this chapter we briefly summarize the essence of our recent work [5], which introduces a coherent control strategy to control bimolecular collisions. Computations designed to examine the range of control possible with this scenario are currently being carried out [6]. 

The outputs of the sensors were used in two closed-loop control strategies developed for combustor performance optimization [7]. The objective of the first strategy, based on an adaptive least-mean squares (LMS) algorithm, was to maximize the magnitude and coherence of temperature oscillations at the forcing frequency /o in the measured region. The LMS algorithm was used to determine... 

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 essential principle of coherent control in the continuum is to create a linear superposition of degenerate continuum eigenstates out of which the desired process (e.g., dissociation) occurs. If one can alter the coefficients a of the superposition at will, then the probabilities of processes, which derive from squares of amplitudes, will display an interference term whose magnitude depends upon the a,. Thus, varying the coefficients a, allows control over the product properties via quantum interference. This strategy forms the basis for coherent control scenarios in which multiple optical excitation routes are used to dissociate a molecule. It is important to emphasize that interference effects relevant for control over product distributions arise only from energetically degenerate states [7], a feature that is central to the discussion below. 

This argument motivates the idea that the way to control photodissociation is to eii e more than one initial state, or in greater generality, to use multiple excitation pathways. In this chapter we demonstrate that such a strategy allows us to actively /rtipijence and control which photodissociation product is formed. These ideas, which firbduce the notion of coherent control, will be later shown to hold true for any lical process, not just for photodissociation. 

Strategies for achieving intra- and intermolecular selectivity are the subject of a very active freld of current research with many open questions. Under the label coherent control it includes approaches that exploit the coherence properties of laser radiation to control chemical reactions. Figure B2.5.18 summarizes the different schemes of intra- and intermolecular selectivity. 

In order to know the true nature of active catalytic species, several control experiments must be carried out to get coherent data. In this way, some authors have proposed strategies, each of them involving various tests. 

The theory of laser control of chemical reactions may be classified into two different domains Laser control by continuous wave (CW) lasers and by laser pulses. The former includes, for example, the strategies of (i) vibra-tionally mediated chemistry [1] and (ii) coherent superpositions of independent excitation routes [2] for experimental demonstrations see (i) Ref. 3 and... 

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