Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

COHERENT CONTROL OF DIRECT AND RESONANT UNIMOLECULAR

Moshe Shapiroa, Paul Brumerb

Published Jan 1, 1986• 0 citations
OpenAlex

Abstract

A General method of controlling branching (direct and resonant) unimolecular reactions, using the coherence of lasers is presented. It is shown that pre-selected products may be obtained, in preference to others, as a result of interference be­ tween decay channels of a superposition of degenerate continuum states. It is shown that such states can be prepared by exciting a superposition of bound states using two coherent light sources with a well defined relative phase. Theoretical limits of coherent control, in direct and compound (statistical like) processes are derived. En­ hanced (often 100%) yields of ~he (chemical) products of interest are obtained. Computational results on the I /1 branching ratios in the photodissociation of FI and CH31, including the effects of initial conditions are presented. In addition, complete blocking-off of a single pre-selected quantum state of a given reaction product, resulting in population inversion with respect to all higher energetic levels, is shown to be attainable.

Related papers

Coherent radiative control of product yields and quantum state populations in photodissociation

Paul W. Brumer

A method for controlling branching unimolecular reactions, developed in collaboration with M. Shapiro of the Weizmann Institute, which uses the coherence of weak lasers, is presented. It is shown that preselected chemical products may be obtained, in preference to others, by utilizing the interference between naturally occurring processes. Our specific application then entails the dissociation of a bound superposition state with control attained by manipulating the relative intensities and phases of coherent laser beams. Enhanced yields of chemical products of interest are shown to result. Similar control is attainable for the populations of individual product quantum states. Computational results on the I*II branching ratios in the photodissociation of CH3, I and FI are presented as examples. Proposals for experiments which demonstrate coherent control present a challenge to the laser community which is well worth accepting.

International Laser Science Conference•Jan 1, 1986•0 citations

Laser control of unimolecular decay yields in the presence of collisions

Moshe Shapiro, Paul W. Brumer

We show that coherent light can be used to control the relative product yield in unimolecular photodissociation, even in the presence of collisions. That is, coherence contributions to the photodissociation, which are responsible for control over the reaction, are sufficiently robust to survive inhomogeneous broadening effects over a substantial temperature range. A number of experimental implementations for control in the presence of collisions are proposed.

The Journal of Chemical Physics•Jun 1, 1989•57 citations

Multiproduct coherent control of photodissociation via two-photon versus two-photon interference

Zhidang Chen, Paul W. Brumer, Moshe Shapiro

We show that the branching ratios into two or three channel photodissociation products can be controlled by a novel resonant two-photon vs two-photon coherent control scenario. The method allows for control even when the initial molecular system is in a mixed state, e.g., in thermal equilibrium, a significant advance for controlling reactions. Essential to the technique is the phase locking between different frequencies which results in cancellation of incoherences due to laser phase jumps. Reduction of uncontrolled background contributions also obtains. The scenario is demonstrated computationally on Na2 photodissociation, where a wide range of control is achieved over branching into two product channels [Na(3s)+Na(4s) vs Na(3s)+Na(3p)] at lower energies and over three product channels at energies above the Na(3s)+Na(3d) threshold.

The Journal of Chemical Physics•May 1, 1993•47 citations

Coherent control of ultrafast bond making and subsequent molecular dynamics: demonstration of final-state branching ratio control

Liat Levin, Daniel M. Reich, Moran Geva +3 more

Abstract Quantum coherent control of ultrafast bond making and the subsequent molecular dynamics is crucial for the realization of a new photochemistry, where a shaped laser field is actively driving the chemical system in a coherent way from the thermal initial state of the reactants to the final state of the desired products. We demonstrate here coherent control over the relative yields of Mg 2 molecules that are generated via photoassociation and subsequently photodriven into different groups of final states. The strong-field process involves non-resonant multiphoton femtosecond photoassociation of a pair of thermally hot magnesium atoms into a bound Mg 2 molecule and subsequent molecular dynamics on electronically excited states. The branching-ratio control is achieved with linearly chirped laser pulses, utilizing the different chirp dependence that various groups of final molecular states display for their post-pulse population. Our joint experimental and theoretical study establishes the feasibility of high degree coherent control over quantum molecular dynamics that is initiated by femtosecond photoassociation of thermal atoms.

arXiv:2104.11786•Journal of Physics B Atomic Molecular and Optical Physics•Jul 9, 2021•0 citations

Coherent control in bulk and nanostructure semiconductors

John E. Sipe, Henry M. van Driel

Laser light has been used as a probe of atoms, molecules, and solids since the invention of the laser. The use of laser light in a more active role, to modify and process surfaces, and initiate chemical reactions, followed shortly thereafter. But usually it is the intensity and the directionality of the laser light that is employed, not necessarily its coherence, and not particularly the fact that it has a well-defined phase. 'Coherence control' can be broadly understood as the set of processes whereby light modifies matter in a way that is critically dependent on the incident light beams possessing well-defined phases. While in a laser matter is manipulated to produce light of the desired properties, in coherent control light is manipulated -- in particular, its phase and intensity is adjusted -- to produce a material response of the desired type. Of the various coherent control processes that are currently being investigated, some involve a transition in the material medium from an initial state to a final state by two or more possible processes. With each of these is associated a quantum mechanical amplitude, and hence the probability for the transition can show interference effects between the two amplitudes, just as in the familiar two-slit interference experiment the probability for the electron to be observed at a given position involves a probability that is the square of the sum of two amplitudes. In quantum interference control (QUIC), the relative phase of the two amplitudes is adjusted by adjusting the relative phase of two polarizations of a single beam, or the relative phase of two beams at different frequencies. It is this particular type of coherent control that is of interest in this communication.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Apr 23, 1998•0 citations

Incoherent interference control of two-photon dissociation

Zhidang Chen, Moshe Shapiro, Paul W. Brumer

Control over product probabilities and channel-specific line shapes in resonant two-photon dissociation is shown to result from quantum interference effects induced by illumination with a second laser. Control over product yield and selectivity is achieved by varying the frequency of this control laser, which need not be coherent with the excitation laser. Computations on ${\mathrm{Na}}_{2}$ photodissociation show that control over product selectivity is extensive.

Physical Review A•Sep 1, 1995•38 citations
A General method of controlling branching (direct and resonant) unimolecular reactions, using the coherence of lasers is presented. It is shown that pre-selected products may be obtained, in preference to others, as a result of interference be­ tween decay channels of a superposition of degenerate continuum states. It is shown that such states can be prepared by exciting a superposition of bound states using two coherent light sources with a well defined relative phase. Theoretical limits of coherent control, in direct and compound (statistical like) processes are derived. En­ hanced (often 100%) yields of ~he (chemical) products of interest are obtained. Computational results on the I /1 branching ratios in the photodissociation of FI and CH31, including the effects of initial conditions are presented. In addition, complete blocking-off of a single pre-selected quantum state of a given reaction product, resulting in population inversion with respect to all higher energetic levels, is shown to be attainable.
A method for controlling branching unimolecular reactions, developed in collaboration with M. Shapiro of the Weizmann Institute, which uses the coherence of weak lasers, is presented. It is shown that preselected chemical products may be obtained, in preference to others, by utilizing the interference between naturally occurring processes. Our specific application then entails the dissociation of a bound superposition state with control attained by manipulating the relative intensities and phases of coherent laser beams. Enhanced yields of chemical products of interest are shown to result. Similar control is attainable for the populations of individual product quantum states. Computational results on the I*II branching ratios in the photodissociation of CH3, I and FI are presented as examples. Proposals for experiments which demonstrate coherent control present a challenge to the laser community which is well worth accepting.
We show that the branching ratios into two or three channel photodissociation products can be controlled by a novel resonant two-photon vs two-photon coherent control scenario. The method allows for control even when the initial molecular system is in a mixed state, e.g., in thermal equilibrium, a significant advance for controlling reactions. Essential to the technique is the phase locking between different frequencies which results in cancellation of incoherences due to laser phase jumps. Reduction of uncontrolled background contributions also obtains. The scenario is demonstrated computationally on Na2 photodissociation, where a wide range of control is achieved over branching into two product channels [Na(3s)+Na(4s) vs Na(3s)+Na(3p)] at lower energies and over three product channels at energies above the Na(3s)+Na(3d) threshold.
Abstract Quantum coherent control of ultrafast bond making and the subsequent molecular dynamics is crucial for the realization of a new photochemistry, where a shaped laser field is actively driving the chemical system in a coherent way from the thermal initial state of the reactants to the final state of the desired products. We demonstrate here coherent control over the relative yields of Mg 2 molecules that are generated via photoassociation and subsequently photodriven into different groups of final states. The strong-field process involves non-resonant multiphoton femtosecond photoassociation of a pair of thermally hot magnesium atoms into a bound Mg 2 molecule and subsequent molecular dynamics on electronically excited states. The branching-ratio control is achieved with linearly chirped laser pulses, utilizing the different chirp dependence that various groups of final molecular states display for their post-pulse population. Our joint experimental and theoretical study establishes the feasibility of high degree coherent control over quantum molecular dynamics that is initiated by femtosecond photoassociation of thermal atoms.
Laser light has been used as a probe of atoms, molecules, and solids since the invention of the laser. The use of laser light in a more active role, to modify and process surfaces, and initiate chemical reactions, followed shortly thereafter. But usually it is the intensity and the directionality of the laser light that is employed, not necessarily its coherence, and not particularly the fact that it has a well-defined phase. 'Coherence control' can be broadly understood as the set of processes whereby light modifies matter in a way that is critically dependent on the incident light beams possessing well-defined phases. While in a laser matter is manipulated to produce light of the desired properties, in coherent control light is manipulated -- in particular, its phase and intensity is adjusted -- to produce a material response of the desired type. Of the various coherent control processes that are currently being investigated, some involve a transition in the material medium from an initial state to a final state by two or more possible processes. With each of these is associated a quantum mechanical amplitude, and hence the probability for the transition can show interference effects between the two amplitudes, just as in the familiar two-slit interference experiment the probability for the electron to be observed at a given position involves a probability that is the square of the sum of two amplitudes. In quantum interference control (QUIC), the relative phase of the two amplitudes is adjusted by adjusting the relative phase of two polarizations of a single beam, or the relative phase of two beams at different frequencies. It is this particular type of coherent control that is of interest in this communication.
Control over product probabilities and channel-specific line shapes in resonant two-photon dissociation is shown to result from quantum interference effects induced by illumination with a second laser. Control over product yield and selectivity is achieved by varying the frequency of this control laser, which need not be coherent with the excitation laser. Computations on Na2{\mathrm{Na}}_{2}Na2​ photodissociation show that control over product selectivity is extensive.