Quantum dynamics of a polar rotor acted upon by time-dependent electromagnetic pulses

As a part of a larger objective to understand the quantum dynamics of a molecular rotor subject to few or single-cycle pulses with a bias, we present results for the simple case when the rotor is acted upon by a unipolar rectangular pulse. In our previous work [J. Chem. Phys. 149, 174109 (2018)], we demonstrated that a rotor interacting with finite-duration Gaussian pulses exhibits "resonances" in the coefficients of a rotational wavepacket initially prepared in its ground state and further leads to the diminishing of the kinetic energy ("rotational arrest") and orientation at particular values of the pulse duration. Herein, we reproduce the above results, both numerically and analytically, with the rectangular pulse and show, in addition, that the orientation becomes vanishingly small at pulse durations corresponding to the quasi-periodic "resonances" independent of the initial free-rotor state. Finally, we discuss experimental realizations and applications of the above control scheme to cold molecular rotors.