Phase sensitive coherent control of atomic excitation in the presence of static electric fields: a frame transformation Stark theory approach

Phase sensitive coherent control on atomic Rydberg states and in the presence of a static electric field is theoretically studied using Harmin's frame transformation theory. It is shown that under the presence of the static field, the total excitation rate of an atomic target by a bichromatic laser field (consisting of a fundamental radiation frequency and of its second harmonic) depends on all the elements of the density-of-states matrix dictating the Stark effect. Some of these off-diagonal matrix elements are inaccessible by any other photoexcitation scheme and affect non-trivially the optimum achievable rate modulation contrast. This fact leads to important qualitative and quantitative differences with respect to static-field-free coherent control. The obtained formal expressions for the phase-controlled excitation rate are applied to the lithium target atom. It is demonstrated that the electric field strength can be used as an additional, externally adjustable, control and manipulation parameter. Finally, it is shown that above the saddle point energy, where quasi-discrete and continuum states coexist, the lineshapes of individual Fano-like resonances can be quite efficiently modified by applying this scheme.