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arXiv:2610.01715

State-selective molecular orientation by vibrational Autler-Townes adiabatic passage

Meng-Yi Yu, Ya-Nan Lv, Cheng Cun-Feng, Shui-Ming Hu

Published Oct 1, 2026• 0 citations
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Abstract

Control of molecular angular momentum orientation enables state-resolved studies of molecular interactions and provides a basis for quantum information processing. Here we propose all-optical Autler-Townes state-selective adiabatic passage (ASAP) to prepare molecules in a single $|J,M\rangle$ sublevel. An Autler-Townes branch created by a strong coupling field is selectively populated and adiabatically mapped onto the target vibrational state. We resolve detuning-dependent rovibrational Autler-Townes splitting in $^{13}$CO$_2$, establishing the spectroscopic basis for the selective excitation of the target dressed branch. The density-matrix model calibrated by these spectra predicts transfer approaching 90\%. The scheme can exploit millisecond vibrational radiative lifetimes within the electronic ground state and extend to polar and nonpolar molecules with infrared-active vibrational modes.

DOI
10.48550/arxiv.2610.01715

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Physical Review A•Jun 18, 2024•4 citations
Control of molecular angular momentum orientation enables state-resolved studies of molecular interactions and provides a basis for quantum information processing. Here we propose all-optical Autler-Townes state-selective adiabatic passage (ASAP) to prepare molecules in a single ∣J,M⟩|J,M\rangle∣J,M⟩ sublevel. An Autler-Townes branch created by a strong coupling field is selectively populated and adiabatically mapped onto the target vibrational state. We resolve detuning-dependent rovibrational Autler-Townes splitting in 13^{13}13CO2_22​, establishing the spectroscopic basis for the selective excitation of the target dressed branch. The density-matrix model calibrated by these spectra predicts transfer approaching 90%. The scheme can exploit millisecond vibrational radiative lifetimes within the electronic ground state and extend to polar and nonpolar molecules with infrared-active vibrational modes.
We suggest that infrared stimulated Raman adiabatic passage, a coherent multiple excitation process, can be used to create a superposition of (2J+1) highly correlated M-state sublevels of a rigid rotor molecule with vibrational level v and rotational level J. This method employs the (v=0,J-2) to (v=2,J) S-branch transition, which is carried out in a counterintuitive manner in which the v=1 to v=2 transition is pumped prior to the v=0 to v=1 transition, causing nearly complete population transfer to the v=2 final level. We use perpendicular and parallel linearly polarized infrared excitation (biaxial excitation). Specifically, the perpendicular polarization connects the v=1 intermediate level to the final vibrational level v=2, and the parallel polarization connects the initial level v=0 to the intermediate level v=1. By this means we break the cylindrical symmetry for an ensemble of vibrationally excited molecules in a rovibrational eigenstate (v=2,J). The angular momentum polarization is determined by the relative phases rather than by the populations of the magnetic M-sublevels. For the phase correlated ensemble, the angular momentum polarization can be considered as a purely quantum mechanical effect. Using a fully general density matrix treatment, we illustrate this approach by considering a beam of carbon monoxide (CO) molecules. We find that significant polarization for J=2, 5, and 10 can be achieved with a cw infrared laser source having modest power (∼100 mW/mm(2)). We believe that this technique is a general one and may offer an experimentally accessible new platform for different applications, from scattering studies with M-state entangled ensembles of molecules to logic gate operations of a quantum computer.
This paper describes an extension of the familiar coherence effects from atomic systems to the molecular regime. Such effects are inherent in the interaction of multiple laser fields with molecular systems. We have observed Autler–Townes splitting and the AC Stark shift in diatomic Lithium using the continuous wave all-optical triple resonance (AOTR) techniques. By using the Autler–Townes effect, we have partially resolved the magnetic sublevels of a molecular rovibrational level in a Doppler broadened sample, allowing all-optical alignment of the angular momentum in excited states of nonpolar molecules. The Autler–Townes effect in a molecular system extends the rovibrational state selectivity of the AOTR excitation technique to magnetic sublevels. PACS Nos.: 33.40tf, 42.50Hz
We have demonstrated Autler-Townes splitting in molecular lithium using continuous wave triple resonance spectroscopy. The Autler-Townes split double resonance lineshape consists of a superposition of several narrower twin peaks, one for each | M j |. The splitting is proportional to | M j | enabling separation of the individual Mj peaks. Thus, excitation of an individual magnetic sublevel can be used to align the angular momentum of nonpolar molecules all-optically. We also propose a novel quantum control scheme based on using a coupling laser to create dressed states of controllable molecular character. Preliminary calculations are presented for variable singlet triplet character.
A density matrix treatment is presented for a general process of preparing polarized molecules through their coherent interaction with two or more infrared photons of different frequencies, each tuned to cause a transition between real levels. This process, which might be called infrared stimulated Raman adiabatic passage, allows complete population transfer to selected rotational-vibrational levels and controls the direction of the rotational angular momentum vector J of the molecule with the possibility of preparing higher moments of the J spatial distribution. HCl molecules in a supersonic molecular beam are considered as a candidate system. Theory predicts that under collision-free conditions two infrared laser pulses of microsecond duration and milliwatt power are able to achieve complete population transfer and alignment of HCl (v=2, J=2, and M=0) for mutually parallel excitation and HCl (v=2, J=2, and M=+/-1) for mutually perpendicular excitation. Orientation of the HCl (v=2, J=2, and M=+/-2) can also be achieved using two circularly polarized pulses of the same helicity. For simplicity, our treatment ignores nuclear spin depolarization, which would be the case for molecules such as (12)C(16)O and (12)C(16)OO(2). Polarized molecules in higher vibrational levels can be prepared using additional infrared pulses.
We investigated the absence of certain bright peaks in Autler-Townes laser excitation spectra of alkali metal atoms. Our research revealed that these dips in the spectra are caused by a specific architecture of adiabatic (or ``laser-dressed'') states in hyperfine (HF) components. The dressed states' analysis pinpointed several cases where constructive and destructive interference between HF excitation pathways in a two-photon excitation scheme limits the available two-photon transitions. This results in a reduction of the conventional two-photon selection rule for the total angular momentum FFF, from ΔF=0,±1ΔF= 0,\pm 1ΔF=0,±1 to ΔF≡0ΔF\equiv 0ΔF≡0. Our discovery presents practical methods for selectively controlling the populations of unresolvable HF FFF-components of ns1/2ns_{1/2}ns1/2​ Rydberg states in alkali metal atoms. Using numerical simulations with sodium and rubidium atoms, we demonstrate that by blocking the effects of HF interaction with a specially tuned auxiliary control laser field, the deviations from the ideal selectivity of the HF components population can be lower than 0.01%0.01\%0.01% for Na and 0.001%0.001\%0.001% for Rb atoms.
Earlier research highlighted the absence of certain bright peaks in Autler-Townes laser excitation spectra of alkali-metal atoms and attributed this phenomenon to a specific architecture of adiabatic (or ``laser-dressed'') states in hyperfine (HF) components. Here we have studied the dressed states' properties in several two-photon excitation schemes where constructive and destructive interferences between HF excitation pathways limit the available two-photon transitions. The analysis reveals a mechanism by which this interference reduces the conventional two-photon selection rule for the total angular momentum FFF, from $\mathrm{\ensuremath{\Delta}}F=0,\ifmmode\pm\else\textpm\fi{}1$ to $\mathrm{\ensuremath{\Delta}}F\ensuremath{\equiv}0$. Our discovery presents a practical method for selectively controlling the populations of unresolvable HF FFF components of ns1/2n{s}_{1/2}ns1/2​ Rydberg states in alkali-metal atoms. Using numerical simulations with sodium and rubidium atoms, we demonstrate that by blocking the effects of HF interaction with a specially tuned auxiliary control-laser field, the deviations from the ideal selectivity of the HF components population can be lower than 0.010.01%0.01 for Na and 0.0010.001%0.001 for Rb atoms.