Biomedical subjects

Werner Jakubetz

Publications and source records attributed to Werner Jakubetz.

5 recordsLinked to original sources

PubMed2006

Phase-sensitive stimulated Raman adiabatic passage in dipolar extended lambda systems.

The authors investigate the possible phase-sensitive behavior of (multiphoton) stimulated Raman adiabatic passage population transfer in extended lambda systems, if more than one state of an anharmonic progression of target levels is accessible in transitions of different photonicities. They use a minimal model four-level system (4LS) with one initial state separated from two target states by an apex state. The parameters of the 4LS are adapted from the bend states of the HCN-HNC system. Using a dressed-state analysis within the rotating wave approximation (RWA), the authors identify phase-dependent diabatic transitions between the two dressed states contributing to the state vector as the mechanism leading to phase-sensitive target populations. The essential features giving rise to the phase dependence are found to be different (non-zero-) diagonal elements of the dipole matrix, i.e., permanent dipole moments, and the presence of a direct two-photon overtone coupling between the apex state and the lower target state which formally enters the RWA Hamiltonian upon inclusion of permanent dipole moments. Among the parameters controlling the extent of the effect are the anharmonic properties of the target progression and the absolute values of the field frequencies, so that in view of the requirement to tune the driving fields into the vicinity of resonance, details of the level structure are of importance. A comparative numerical study executed without invoking RWA shows that qualitatively there are similar trends in the appearance of phase sensitivity, although the effects are considerably more pronounced in the full treatment. In the full treatment the authors also explore off-resonance conditions and discuss the signatures of phase sensitivity in the target populations.

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PubMed2006

Counterdiabatic suppression of background state population in resonance leaking by controlling intermediate branching.

The counterdiabatic principle [M. Demirplak and S. A. Rice, J. Phys. Chem. A 107, 9937 (2003)] is used in a pragmatic way to formulate a practical control strategy for perturbed population transfer. Interpreting the appearance of population in undesirable intruder or background states as phenomenological consequences of diabatic perturbations, such branching is suppressed as soon as it arises. By invoking a penalty term that is sensitive to any transitional population in undesirable levels, a correction field is created which effectively prevents diabatic behavior. This strategy is applied to the control of background state population in multiphoton excitations. For a model five-level system we show that leaking of a resonant three-photon transition to a background state can readily be suppressed by simple correction fields obtained from our intermediate-branching driven implementation of counterdiabatic control.

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PubMed2004

Pulse-pair control of resonance leaking in molecular multiphoton transitions.

We use model five-level systems to study resonance leaking of pi-pulse-induced multiphoton (MP) transitions along a strongly coupled anharmonic ladder. We demonstrate that the presence of a weakly bound background state attached to the ladder either in linear or Lambda configuration can have very pronounced effects on resonant MP ladder transitions, including essentially complete quenching of the primary transition. We also develop control strategies for the elimination of background state population based on phase-adjusted Gaussian pulse pairs and discuss the underlying control mechanisms. Finally we show that these strategies are effective in realistic molecular many-level systems. In particular, we demonstrate efficient pulse-pair control of resonance leaking in a 165-level system modeling vibrational excitation in HCN.

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PubMed2004

Molecular isomerization induced by ultrashort infrared pulses. I. Few-cycle to sub-one-cycle Gaussian pulses and the role of the carrier-envelope phase.

Using 550 previously calculated vibrational energy levels and dipole moments we performed simulations of the HCN-->HNC isomerization dynamics induced by sub-one-cycle and few-cycle IR pulses, which we represent as Gaussian pulses with 0.25-2 optical cycles in the pulse width. Starting from vibrationally pre-excited states, isomerization probabilities of up to 50% are obtained for optimized pulses. With decreasing number of optical cycles a strong dependence on the carrier-envelope phase (CEP) emerges. Although the optimized pulse parameters change significantly with the number of optical cycles, the distortion by the Gaussian envelope produces nearly equal fields, with a positive lobe followed by a negative one. The positions and areas of the lobes are also almost unchanged, irrespective of the number of cycles in the half-width. Isomerization proceeds via a pump-dumplike mechanism induced by the sequential lobes. The first lobe prepares a wave packet incorporating many delocalized states above the barrier. It is the motion of this wave packet across the barrier, which determines the timing of the pump and dump lobes. The role of the pulse parameters, and in particular of the CEP, is to produce the correct lobe sequence, size and timing within a continuous pulse.

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PubMed2004

Molecular isomerization induced by ultrashort infrared pulses. II. Pump-dump isomerization using pairs of time-delayed half-cycle pulses.

We investigate population transfer across the barrier in a double-well potential, induced by a pair of time-delayed single-lobe half-cycle pulses. We apply this setup both to a one-dimensional (1D) quartic model potential and to a three-dimensional potential representing HCN-->HNC isomerization. Overall the results for the two systems are similar, although in the 3D system some additional features appear not seen in the 1D case. The generic mechanism of population transfer is the preparation by the pump pulse of a wave packet involving delocalized states above the barrier, followed by the essentially 1D motion of the delocalized part of wave packet across the barrier, and the eventual de-excitation by the dump pulse to localized states in the other well. The correct timing is given by the well-to-well passage time of the wave packet and its recurrence properties, and by the signs of the field lobes which determine the direction and acceleration or deceleration of the wave packet motion. In the 3D system an additional pump-pump-dump mechanism linked to wave packet motion in the reagent well can mediate isomerization. Since the transfer time and the pulse durations are of the same order of magnitude, there is also a marked dependence of the dynamics and the transfer yield on the pulse duration. Our analysis also sheds light on the pronounced carrier envelope phase dependence previously observed for isomerization and molecular dissociation with one-cycle and sub-one-cycle pulses.

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