It is analytically and numerically shown that the coherent tunnelling between the individual wells of a symmetrical double well potential can be totally suppressed when it is driven by a periodic series of δ function in time, depending on the time period and strength of the δ function. We have applied time dependent perturbation theory to have an understanding over the process. In absence of any kind of perturbation, the average position of the particle makes a sinusoidal oscillation between two wells. With the application of a periodic δ function, the amplitude and the frequency of the oscillation both get modified. In this article we have explored how the frequency and strength of the applied perturbation controls the quantum dynamics of tunnelling and finally, how these parameters drive the system towards a complete stand still situation, which is described as coherent destruction of tunnelling.

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The surfaces of and F2 are two well separated surfaces modeled by two Morse potentials. In presence of a field, these two surfaces couple and transition from to F2 takes place resulting in the detachment of an electron. We have applied Simulated Annealing (SA) technique to design the polychromatic field which results in ∼ 95% probability of photo detachment (Pd). Also we have designed a field to achieve photo detachment followed by dissociation of FF bond with nearly 38% dissociation probability. F2 being a homo nuclear diatomic molecule, promotion to the continuum states by directly exciting it from its ground vibrational state is an impossibility and our method appears to be a feasible solution if the target is to break the FF bond.