Optical cycling, a phenomenon in which atoms or molecules rapidly emit photons after optical excitation in a repeated cycle, is important in laser cooling and trapping, as well as state preparation and measurement. Theoretical and experimental works [1, 2, 3] show that aromatic compounds functionalized with an M-O unit for optical cycling (M = Ca or Sr) can be made suitable for repeated photon scattering. Here, we report the production and spectroscopic characterization of strontium (I) phenoxide (SrOC6H5, or SrOPh) and variants featuring electron-withdrawing groups designed to suppress vibrational excitation during spontaneous emission from the electronically excited state. By using dispersed laser-induced fluorescence spectroscopy, we discovered that the cycling closure of these species, which is the decoupling of vibrational state changes from spontaneous optical decay, is high, which is consistent with theoretical predictions. A high-resolution, rotationally resolved laser excitation spectrum is also recorded for SrOPh, allowing the estimation of spectroscopic constants and identification of candidate optical cycling transitions for future work. The results show the promise of strontium phenoxides for laser cooling and quantum state detection at the single-molecule level. This work also suggests that a larger class of molecules than previously realized may be amenable to laser cooling. (1) Dickerson, C. E.; et al. Phys. Rev. Lett. 2021, 126, 123002. (2) Dickerson, C. E.; et al. J. Phys. Chem. Lett. 2021, 12, 3989–3995. (3) Zhu, G. Z.; et al. Nat. Chem. 2022, 14, 995–999.

The unique optical cycling properties of metal-ligand molecules containing alkaline earth(-like) elements are essential to laser cooling and trapping of molecules. As the chemical complexity of target systems increases, so does the necessity of understanding the relationships between their chemical bonding, electronic structure, and critical spectroscopic properties. We present a comprehensive isotopic study of the microwave rotational spectra of the metal-bearing acetylides MgCCH, CaCCH, SrCCH, and YbCCH in their ground ² Σ⁺ electronic states. Their precise semi-experimental equilibrium geometries have been derived using high-accuracy theoretical corrections for electronic and zero-point motion effects. The well resolved hyperfine structure of the ^1,2H, ¹³C, and metal nuclear spins provides complementary information on the distribution and hybridization of the optically active metal-centered unpaired electron. Our measurements of this reference family of molecules reveal trends in chemical bonding and structure that are correlated with the electronic properties that promote efficient optical cycling. The development of such chemical design principles supports next-generation experiments in precision measurement and quantum control of complex polyatomic molecules.

The research potential of radioactive molecules for both fundamental and applied science has recently been recognized [1,2] and significant progress has been marked at ISOLDE on both the production and the spectroscopy [3,4] of radioactive molecules. In addition to the first laser spectroscopy of RaF at the collinear resonance ionization spectroscopy (CRIS) experiment [3,4], which was triggered by theoretical predictions in Ref. [5], and its subsequent high-resolution study, the CRIS collaboration recently performed the first laser spectroscopy of AcF [6]. AcF has been proposed as a promising system for the first measurement of a nuclear Schiff moment across the nuclear chart. Simultaneously, experimental and theoretical progress in the excited electronic states of RaF and the manifestation of nuclear observables in molecular spectra [7] carried out by members of the CRIS collaboration has highlighted the potential of laser spectroscopy of radioactive molecules at radioactive ion beam facilities to probe nuclear and molecular observables that are not easily accessible by other methods and systems. In this talk, recent results by the CRIS collaboration on the laser spectroscopy of AcF will be presented, along with theoretical work on the spectroscopy of lighter radioactive molecules that can provide access to nuclear and molecular observables that cannot be studied via other methods. The future directions of laser-spectroscopic studies of radioactive molecules at CRIS will also be discussed. [1] arXiv:2302.02165 (2023) [2] CERN-INTC-2021-017 (2021) [3] Nature 581, 396 (2020) [4] Physical Review Letters 127, 033001 (2021) [5] Phys. Rev. A 82, 052521 (2010) [6] CERN-INTC-2021-053 (2021) [7] Physical Review X 13 (1), 011015 (2023) The complete author list is omitted from this abstract due to length constraints but will appear in the talk.

The Cold molecule Nuclear Time-Reversal EXperiment (CeNTREX) aims to look for the fundamental time-reversal (T) symmetry violations in the hadronic sector. Violation of T symmetry is a necessary condition to dynamically generate the asymmetry in matter and anti-matter we observe in the universe. Many extensions of the standard model imply additional sources of T-violation larger than the standard model prediction. CeNTREX utilizes Ramsey interferometry on cryogenic beam of thallium fluoride (TlF) molecules to look for shifts in nuclear magnetic resonance frequencies in ²⁰⁵Tl nucleus when it is electrically polarized. To increase sensitivity, CeNTREX employs lasers, microwaves and electric fields to prepare and manipulate molecular quantum states. Laser-induced fluorescence readout of TlF then provides information on T-violating phase acquired during the Ramsey interferometry. We project significant improvements in the experimental upper bounds of various T-violating parameters. Here, we present on the motivation and progress of the experiment as well as the techniques involved.

Recently, enantiomer-specific state transfer (ESST) was demonstrated using frequency-, phase-, and polarization-controlled microwaves [1]. This method allows to populate or depopulate a rotational state of a chosen enantiomer, providing a way of quantum-controlled chiral separation. In the past, the transfer efficiency of ESST was limited by the initial thermal population of the energy levels participating in ESST [1,2] and by spatial degeneracy [3]. To address these prior limitations, we developed a new experimental scheme by combining optical methods [4] with microwave spectroscopy. This increased the efficiency of ESST by over a factor of ten compared to previously reported values [5]. Our scheme enables a quantitative comparison between experiment and theory involving the absolute ground state level. I will discuss recent experimental results and our ongoing work aiming at perfect ESST in my presentation. [1] S. Eibenberger, J. Doyle, D. Patterson, Phys. Rev. Lett. 118, 123002 (2017) [2] C. Pérez, A. L. Steber, S. R. Domingos, A. Krin, M. Schnell, Angew. Chem. Int. Ed. 56, 12512 (2017) [3] K. K. Lehmann, J. Chem. Phys. 149, 094201 (2018) [4] A. O. Hernandez-Castillo, J. Bischoff, J. H. Lee, J. Langenhan, M. Karra, G. Meijer, and S. Eibenberger-Arias, Phys. Chem. Chem. Phys. 23, 7048-7056 (2021) [5] J. H. Lee, J. Bischoff, A. O. Hernandez-Castillo, B. Sartakov, G. Meijer, and S. Eibenberger-Arias, Phys. Rev. Lett. 128, 173001 (2022)

Chiral molecules are present ubiquitously in nature. They have two enantiomeric forms, which are mirror images of each other and cannot be superimposed onto one another through rotation. Due to the mirror-imaged mass distribution, the two enantiomers have the same moments of inertia (I_A, I_B, and I_C) in the principal axis system and thus have almost identical rotational signatures and cannot be distinguished with conventional microwave spectroscopy. In order to achieve chiral analysis for the chiral molecules in the gas phase, microwave three-wave mixing (M3WM) technique has been developed,D. Patterson, M. Schnell, J. M. Doyle, Nature 497, 475–477 (2013).hich exploits three-dimensional light-matter interactions in the dipole approximation. Beyond chiral analysis, this technique is further extended to achieve enantiomer-selective chiral control in the rotational state of interest, which is capable of inducing a state-specific enantiomeric excess “on the fly” when starting from a racemic mixture. Previously, it has been reported that enantiomeric excess of about 0.5% and 6% were successfully generated using this approach with 1,2-propanediolS. Eibenberger, J. Doyle, D. Patterson, Phys. Rev. Lett. 118, 123002 (2017).nd carvone,C. Pérez, A. L. Steber, S. R. Domingos, A. Krin, D. Schmitz, M. Schnell, Angew. Chem. Int. Ed. 56, 12512–12517 (2019).espectively. The enantiomer in excess can be induced selectively by tuning the phase of the microwave pulses. Here we present our recent investigation aimed at further improving the efficiency of this technique with solely microwave fields. We performed the population transfer experiment with a racemic sample of 2-trifluoromethyl oxirane and show that an enantiomeric excess of about 13% was induced by employing a population transfer scheme starting from the ground rotational state |0₀₀〉, which diminishes the spatial degeneracy of the rotational states. Furthermore, by depleting the initial thermal population with a resonant π-pulse or a microwave chirp in the rapid adiabatic passage regime, the obtained enantiomeric excess can be significantly improved to over 40%. These effects will be discussed in detail along with the theoretical simulations.

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Footnotes:

D. Patterson, M. Schnell, J. M. Doyle, Nature 497, 475–477 (2013).w S. Eibenberger, J. Doyle, D. Patterson, Phys. Rev. Lett. 118, 123002 (2017).a C. Pérez, A. L. Steber, S. R. Domingos, A. Krin, D. Schmitz, M. Schnell, Angew. Chem. Int. Ed. 56, 12512–12517 (2019).r

Metrological measurements of rovibrational frequencies in molecular hydrogen provide stringent tests for the most advanced theoretical calculations and for searching for physics beyond the standard model. We will present the accurate transition frequencies of a series of lines belonging to the (2-0) vibrational band of H₂ near 1.2 μm. These weak electric-quadrupole transitions were measured at room temperature by comb referenced cavity ring-down spectroscopy and are the first H₂ (2-0) transition frequencies referenced to an absolute frequency standard. Accurate transition frequencies determination - up to three orders of magnitude better than previous measurements - will be presented. The impact of the line profile on zero-pressure line centers will be evaluated. These transition frequencies are used to infer the separation of lower energy levels in the vibrational ground state. All these experimental results will be compared to the most recent calculated frequencies.