Abstract
A coherent mechanism of robust population inversion in atomic and molecular systems by a chirped field is presented. It is demonstrated that a field of sufficiently high chirp rate imposes a certain relative phase between a ground and excited state wavefunction of a two-level system. The value of the relative phase angle is thus restricted to be negative and close to 0 or - pi for positive and negative chirp, respectively. This explains the unidirectionality of the population transfer from the ground to the excited state.In a molecular system composed of a ground and excited potential energy surface the symmetry between the action of a pulse with a large positive and negative chirp is broken. The same framwork of the coherent mechanism can explain the symmetry breaking and the population inversion due to a positive chirped field.
Highlights
A coherent mechanism of robust population inversion in atomic and molecular systems by a chirped field is presented
The direct approach to population inversion by applying a π pulse is plagued by the inability to precisely control the intensity and time duration of the excitation pulse
For a molecular system composed of two potential surfaces (TPS) the problem of robust complete population transfer from the ground electronic state to the excited one becomes more difficult
Summary
The value of the relative phase angle is restricted to be negative and close to 0 or −π for positive and negative chirp, respectively This explains the unidirectionality of the population transfer from the ground to the excited state. For a molecular system composed of two potential surfaces (TPS) the problem of robust complete population transfer from the ground electronic state to the excited one becomes more difficult. In the present letter we present a unified viewpoint based on a simple coherent control analysis which can explain the mechanism of robust complete population transfer in both the two-level system (TLS) as well as for the two potential surface (TPS) scenario. I, were chosen by the criteria of a correct representation of the wavepacket in coordinate as well as in momentum spaces
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