Precise quantum control of molecular rotation toward a desired orientation
Qian-Qian Hong, Daoyi Dong, Niels E. Henriksen, Franco Nori, Jun He, Chuan‐Cun Shu
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 multilevel 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 <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:msub> <a:mrow> <a:mo>|</a:mo> <a:mrow> <a:mo>〈</a:mo> <a:mo form="prefix">cos</a:mo> <a:mi>θ</a:mi> <a:mo>〉</a:mo> </a:mrow> <a:mo>|</a:mo> </a:mrow> <a:mi>max</a:mi> </a:msub> </a:math> 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 multilevel 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.