Limitations on the strong field coherent control of degenerate states

Coherent control of quasi-degenerate stationary-like states via multiple resonances

We use three bosons held in a depth-tilt combined-modulated double-well to study coherent control of quantum transitions between quasi-degenerate stationary-like states (QDSLSs) with the same quasienergy. Within the high-frequency approximation and for multiple-resonance conditions, we analytically obtain the different QDSLSs including the maximal bipartite entangled states, which enable us to manipulate the transitions between QDSLSs without the observable multiphoton absorption and to simulate a two-qubit system with the considered bosons. The analytical results are confirmed numerically and good agreement is shown. The quantum transitions between QDSLSs can be observed and controlled by adjusting the initial and the final atomic distributions in the currently proposed experimental setup, and possess potential applications in qubit control based on the bipartite entangled states and in engineering quantum dynamics for quantum information processing.

Entanglement in interference-based quantum control: the wave function is not enough

We analyze the way entanglement affects features of interference-based quantum control. We show that quantum interferences vanishes in several cases in the process of extracting probabilities from wave functions. As an example, we discuss the loss of quantum interferences when tracing over number states of the radiation field. We also consider the way in which controllability is reduced when tracing over an entire manifold of states whose cumulative probability we wish to control. Finally, we show that it is impossible to control the relative populations of degenerate states (occurring, e.g., in dissociation and chemical reactions) when the relevant transition amplitude is factorizeable, i.e., when it can be written as a product of a purely classical field-dependent part and a purely materialdependent part. Differences between entanglement and non-factorizability of amplitudes are emphasized.