Biomedical subjects

P Brumer

Publications and source records attributed to P Brumer.

At least 19 recordsLinked to original sources

PubMed2006

Quantum control of internal conversion in 24-vibrational-mode pyrazine.

Quantum control of the S(2)-->S(1) internal conversion in a complete 24-mode dimensionality model of pyrazine is demonstrated. The fully quantum mechanical study makes use of the recently developed "QP algorithm" for performing accurate computations of projected quantum dynamics and the role of overlapping resonances in control. The results are extremely encouraging, demonstrating active control over internal conversion so as to almost completely suppress the process over time scales of approximately 50-100 fs [well in excess of the natural internal conversion times (approximately 20 fs)] or to accelerate it to complete internal conversion in less than 5 fs. A number of new diagnostics are introduced to demonstrate the significance of overlapping-resonance contributions to control. Control is far better than for a reduced dimensionality model of pyrazine, presumably because of the increased degree of overlap between bound state resonances existing in the full dimensionality case.

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PubMed2006

Aspects of quantum coherence in the optical Bloch equations.

Aspects of coherence and decoherence are analyzed within the optical Bloch equations. By rewriting the analytic solution in an alternate form, we are able to emphasize a number of unusual features: (a) despite the Markovian nature of the bath, coherence at long times can be retained; (b) the long-time asymptotic degree of coherence in the system is intertwined with the asymptotic difference in level populations; (c) the traditional population-relaxation and decoherence times, T1 and T2, lose their meaning when the system is in the presence of an external field, and are replaced by more general overall time scales; (d) increasing the field strength, quantified by the Rabi frequency Omega, increases the rate of decoherence rather than reducing it, as one might expect; and (e) maximum asymptotic coherence is reached when the system parameters satisfy Omega2=1(T1T2).

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PubMed2001

Coherent control of quantum chaotic diffusion.

Extensive coherent control over quantum chaotic diffusion using the kicked rotor model is demonstrated and its origin in deviations from random matrix theory is identified. Further, the extent of control in the presence of external decoherence is established. The results are relevant to both areas of quantum chaos and coherent control.

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PubMed2000

Coherently controlled nanoscale molecular deposition.

Quantum interference effects are shown to provide a means of controlling and enhancing the focusing of a collimated neutral molecular beam onto a surface. The nature of the aperiodic pattern formed can be altered by varying laser field characteristics and the system geometry.

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PubMed2000

Coherently controlled asymmetric synthesis with achiral light

A laser-based method of increasing the enantiomeric excess of a chiral enantiomer in a racemic mixture is described. Neither the initial reagents nor the incident light need be chiral. Both formal and computational results show that enhancement of the enantiomer of choice, controlled by laser parameters, can be extensive.

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PubMed1999

Decoherence and correspondence in conservative chaotic dynamics.

The quantum and classical dynamics of a conservative nonlinear Hamiltonian system in the chaotic regime are compared in the absence and presence of decoherence effects. Results show marked improvement in classical-quantum correspondence with the introduction of decoherence, even though the initial quantum dynamics is far from the semiclassical limit.

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PubMed1996