Steering quantum transitions between three crossing energy levels

TL;DR

This paper develops an accurate analytic model for three-state quantum transitions with linearly changing energies and pulse-shaped interactions, capturing quantum interference effects and enabling precise control in various quantum systems.

Contribution

The authors derive a highly accurate analytic approximation for three-state quantum transitions using pairwise Landau-Zener models, extending the understanding of quantum interference and control.

Findings

Analytic approximation matches numerical results with high accuracy.

Derived estimates for excitation profile width and superposition creation.

Applicable to various quantum systems like alkali atoms and quantum rotors.

Abstract

We calculate the propagator and the transition probabilities for a coherently driven three-state quantum system. The energies of the three states change linearly in time, whereas the interactions between them are pulse-shaped. We derive a highly accurate analytic approximation by assuming independent pairwise Landau-Zener transitions occurring instantly at the relevant avoided crossings, and adiabatic evolution elsewhere. Quantum interferences are identified, which occur due to different possible evolution paths in Hilbert space between an initial and a final state. A detailed comparison with numerical results for Gaussian-shaped pulses demonstrates a remarkable accuracy of the analytic approximation. We use the analytic results to derive estimates for the half-width of the excitation profile, and for the parameters required for creation of a maximally coherent superposition of the three states. These results are of potential interest in ladder climbing in alkali atoms by chirped laser pulses, in quantum rotors, in transitions between Zeeman sublevels of a J=1 level in a magnetic field, and in control of entanglement of a pair of spin-1/2 particles. The results for the three-state system can be generalized, without essential difficulties, to higher dimensions.