Precise Quantum Control of Molecular Rotation Toward a Desired Orientation

TL;DR

This paper introduces an analytical framework for precisely controlling molecular rotation states using optimized laser pulses, enabling near-perfect molecular orientation and superposition in ultracold polar molecules.

Contribution

The work presents a multi-level pulse-area theorem-based approach for exact control of rotational states, achieving high orientation with minimal control parameters.

Findings

Achieved a maximum orientation value above 0.99

Generated 15 distinct rotational superpositions

Demonstrated near-global optimal control in a finite-dimensional subspace

Abstract

The lack of a direct map between control fields and desired control objectives poses a significant challenge in applying quantum control theory to quantum technologies. Here, we propose an analytical framework to precisely control a limited set of quantum states and construct desired coherent superpositions using a well-designed laser pulse sequence with optimal amplitudes, phases, and delays. This theoretical framework that corresponds to a multi-level pulse-area theorem establishes a straightforward mapping between the control parameters of the pulse sequence and the amplitudes and phases of rotational states within a specific subspace. As an example, we utilize this approach to generate 15 distinct and desired rotational superpositions of ultracold polar molecules, leading to 15 desired field-free molecular orientations. By optimizing the superposition of the lowest 16 rotational states, we demonstrate that this approach can achieve a maximum orientation value of $|\langle\cos\theta\rangle|_{\rm{max}}$ above 0.99, which is very close to the global optimal value of 1 that could be achieved in an infinite-dimensional state space. This work marks a significant advancement in achieving precise control over multi-level subsystems within molecules. It holds potential applications in molecular alignment and orientation, as well as in various interdisciplinary fields related to the precise quantum control of ultracold polar molecules, opening up considerable opportunities in molecular-based quantum techniques.