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The Journal of Chemical Physics

Fast enantioconversion of chiral mixtures based on effective two-level models

Jian-Jian Cheng, Yao Du, Xi Yang Zhao, Junling Che

Published Oct 10, 2025• 0 citations
Publisher

Abstract

We propose an interesting method for the fast enantioconversion of chiral mixtures, leveraging a modified four-level double-Δ model that operates entirely through coherent interactions. By simplifying the model to an effective two-level system, we eliminate the need for intermediate achiral excited states and their associated time-consuming relaxation steps. This approach accelerates enantioconversion by directly evolving the two chiral ground states through population transfer, offering a more efficient alternative to traditional methods such as laser distillation. Our method, which obviates the need for precise pulse shape control, enables highly efficient enantiomeric conversion on the microsecond timescale. This improvement is particularly beneficial in experimental conditions with limited operational time or short enantiomeric lifetimes, making it a powerful tool for enantioconversion of chiral mixtures.

DOI
10.1063/5.0284446

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We propose an interesting method for the fast enantioconversion of chiral mixtures, leveraging a modified four-level double-Δ model that operates entirely through coherent interactions. By simplifying the model to an effective two-level system, we eliminate the need for intermediate achiral excited states and their associated time-consuming relaxation steps. This approach accelerates enantioconversion by directly evolving the two chiral ground states through population transfer, offering a more efficient alternative to traditional methods such as laser distillation. Our method, which obviates the need for precise pulse shape control, enables highly efficient enantiomeric conversion on the microsecond timescale. This improvement is particularly beneficial in experimental conditions with limited operational time or short enantiomeric lifetimes, making it a powerful tool for enantioconversion of chiral mixtures.
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Abstract Laser-assisted enantio-conversion is an ambitious issue related to chiral molecules in atomic, molecular, and optical physics. The theoretical laser-distillation method was proposed to realize enantio-conversion based on a four-level double-Δ model of two degenerated chiral ground states and two achiral excited states. Here, we re-investigate and improve the laser-distillation method so that a chiral mixture can be converted to an enantiopure sample of the desired chirality, i.e. complete enantio-conversion, which has not been discussed in previous theoretical works on the laser-distillation method. Since the undesired chirality may be inefficient, or even cause serious side effects in pharmacology, our work provides an important improvement to the original theoretical works on laser-assisted enantio-conversion.
Enantio-conversion with the help of electromagnetic fields is an essential issue due to the chirality dependence of many chemical, biological, and pharmaceutical processes. Here, we propose a method for this issue based on a five-level double-$\mathrm{\ensuremath{\Delta}}$ model of chiral molecules. By utilizing the breaking of left-right symmetry in two $\mathrm{\ensuremath{\Delta}}$-type substructures, we can establish chiral-state-selective excitations with one chiral ground state being excited to an achiral excited state and the other one being undisturbed. In the meanwhile, the achiral excited state will relax to two chiral ground states. The two effects simultaneously acting on chiral mixtures can convert molecules of different chiralities to ones of the same chirality, i.e., enantio-conversion via optical pumping. We numerically show that highly efficient enantio-conversion can be achieved. Our method works in the appearance of decoherences and without the precise control of pulse durations (pulse areas) or pulse shapes. These advantages offer it promising features in promoting the future exploration of enantio-conversion.
ABSTRACT We propose a universal scheme applicable to various multistate chiral molecular configurations, achieving 100 chiral resolution with the advantages of simple procedures and high precision. By reversely designing Hamiltonians with 4D rotation, we can determine the parameters of the different four‐level Hamiltonians to realize the desired quantum state control. For the four‐level quantum systems with anti‐Y configuration and double‐ configuration, we can transfer the population of the bi‐chiral system completely from the different initial state to the target state for the left‐handed molecules and to the target state for right‐handed molecules. More importantly, we can accurately change the chirality of the N‐type four‐level quantum system by transferring the populations between states and . Furthermore, the inverse engineering method demonstrates that the fidelity of the final state remains above 95 over a wide range of parameters in the presence of Rabi and detuning errors, and energy relaxation. The result offers an effective, precise, and reliable method for rapid enantiomer conversion in different four‐level chiral systems, which may shed light on the further application of exploring quantum information techniques to achieve the effective enantioselective control of short‐lived enantiomers.
Developing effective methods to measure the enantiomeric excess of chiral mixtures is one of the major topics in chiral molecular research but remains challenging. An enantiodetection method via two-dimensional (2D) spectroscopy based on a four-level model containing a cyclic three-level system (CTLS) of chiral molecules was recently proposed and demonstrated, but with a strict condition of one-photon resonance (where three driving fields are exactly resonantly coupled to the three electric dipole transitions) in the CTLS and narrow-band probe-pulse assumption. Here, we extend the 2D spectroscopy method to more general experimental conditions, with three-photon resonance (where the sum of the two smaller frequencies among the three driving fields equals the third one) and a broadband probe pulse. Our method remains effective on enantiodetection with the help of experimental techniques such as the chop-detection method, which is used to eliminate the influence of the other redundant levels that exist in the real system of chiral molecules. Under these more general conditions, the enantiomeric excess of the chiral mixture is estimated by taking an easily available standard sample (usually the racemic mixture) as the reference.