Precise quantum control of unidirectional field-free molecular orientation

TL;DR

This paper introduces a theoretical method for achieving long-lasting, unidirectional molecular orientation in symmetric top molecules using a single control pulse, emphasizing initial state selection and quantum coherence.

Contribution

It presents a novel quantum control strategy for unidirectional orientation by manipulating two rotational states with a single pulse, simplifying previous complex schemes.

Findings

Effective control of orientation direction and magnitude demonstrated

Numerical validation for methyl iodide molecules shows feasibility

Highlights importance of initial state and coherence in orientation

Abstract

The capability to control molecular rotation for field-free orientation, which arranges molecules in specific spatial directions without external fields, is crucial in physics, chemistry, and quantum information science. However, conventional methods typically lead to transient orientations characterized by periodic directional reversals and necessitate the generation of coherent superpositions across a broad spectrum of rotational states of ultracold molecules. In this work, we develop a theoretical framework for achieving unidirectional field-free orientation by selectively manipulating two specific rotational states of symmetric top molecules. By leveraging the interplay between coherent superpositions and the precise selection of initial states, we demonstrate that both the maximum achievable orientation and its direction can be effectively controlled. To attain the desired two-state orientation, we present a quantum control strategy that utilizes a single control pulse, significantly simplifying the complexities of conventional multistate or multipulse schemes. Numerical simulations validate the effectiveness and feasibility of this approach for methyl iodide (CH$_3$I) molecules, even when accounting for molecular centrifugal distortion.The results highlight the critical roles of initial-state selection and quantum coherence in achieving long-lasting, high unidirectional molecular orientation, opening new directions in stereochemistry, precision spectroscopy, and quantum computing.