arXiv subjects

Benjamin L. Augenbraun

Publications and source records attributed to Benjamin L. Augenbraun.

At least 19 recordsLinked to original sources

arXiv2026

Elucidating Au-C Bonding via Laser Spectroscopy of Gold Monocarbide

Gold monocarbide (AuC) has been produced and characterized using laser spectroscopy, representing the first reported observation of AuC. We recorded the optical spectrum of gas-phase AuC between 400 nm and 700 nm, assigning excitations from the $\mathrm{X}\,^2Π_{1/2}( (2σ)^2 (2π)^1 )$ ground state to states arising from the $(2σ)^2 (3σ^\ast)^1 $ and $(2σ)^1 (2π)^2 $ configurations. Dispersed-fluorescence spectra are used to study the vibrational and spin-orbit structure of the ground state, branching ratios and radiative lifetimes of the excited states, and the Au--C bond dissociation energy. A molecular orbital diagram is used to rationalize the nature of AuC's low-lying electronic states. The data serve as valuable benchmarks of relativistic theory and are relevant to quantum science and precision measurements with cold molecules.

physics.atom-ph↗

arXiv2025

Hyperfine-Resolved Spectroscopy of Dysprosium Monoxide (DyO) for Precision Measurements of the Nuclear Schiff Moment

We perform laser spectroscopy of dysprosium monoxide (DyO) to determine the hyperfine structure of the ground X8 and excited [17.1]7 states in the $^{161}$Dy and $^{163}$Dy isotopologues. These dysprosium nuclei have non-zero nuclear spin and dynamical octupole deformation, which gives them high sensitivity to time-reversal-violating new physics via the nuclear Schiff moment (NSM). The DyO molecule was recently identified as being amenable to optical cycling -- the basis for many laser cooling and quantum control techniques -- which makes it a practical candidate for NSM searches. The measurements reported here are prerequisites to implementing optical cycling, designing precision measurement protocols, and benchmarking calculations of molecular sensitivity to symmetry-violating effects. The measured hyperfine parameters are interpreted using simple molecular orbital diagrams and show excellent agreement with relativistic quantum chemical calculations.

physics.atom-ph↗

arXiv2024

Optical Cycling and Sensitivity to the Electron's Electric Dipole Moment in Gold-Containing Molecules

We propose diatomic molecules built from gold and carbon-group atoms as promising candidates for optical cycling and precision measurements. We show that this class of molecules (AuX, X = C, Si, Ge, Sn, Pb) features laser-accessible electronic transitions with nearly diagonal Franck-Condon factors. The $^2Π_{1/2}$ ground states can be easily polarized in the laboratory frame and have near-zero magnetic moments, valuable features for quantum science and precision measurement applications. The sensitivities of AuX molecules to the electron electric dipole moment (EDM) are found to be favorable, with effective electric fields of 10-30 GV/cm. Together, these features imply that AuX molecules may enable significantly improved searches for time-reversal symmetry violation.

physics.atom-ph↗

arXiv2023

Laser spectroscopy of aromatic molecules with optical cycling centers: strontium (I) phenoxides

We report the production and spectroscopic characterization of strontium (I) phenoxide ($\mathrm{SrOC}_6\mathrm{H}_5$, or SrOPh) and variants featuring electron-withdrawing groups designed to suppress vibrational excitation during spontaneous emission from the electronically excited state. Optical cycling closure of these species, which is the decoupling of vibrational state changes from spontaneous optical decay, is found by dispersed laser-induced fluorescence spectroscopy to be high, in accordance with theoretical predictions. A high-resolution, rotationally-resolved laser excitation spectrum is recorded for SrOPh, allowing the estimation of spectroscopic constants and identification of candidate optical cycling transitions for future work. The results confirm the promise of strontium phenoxides for laser cooling and quantum state detection at the single-molecule level.

physics.atom-ph↗

arXiv2023

Direct Laser Cooling of Polyatomic Molecules

Over the past decade, tremendous progress has been made to extend the tools of laser cooling and trapping to molecules. Those same tools have recently been applied to polyatomic molecules (molecules containing three or more atoms). In this review, we discuss the scientific drive to bring larger molecules to ultralow temperatures, the features of molecular structure that provide the most promising molecules for this pursuit, and some technical aspects of how lasers can be used to control the motion and quantum states of polyatomic molecules. We also present opportunities for and challenges to the use of polyatomic molecules for science and technology.

physics.atom-ph↗

arXiv2022

Zeeman-Sisyphus Deceleration for Heavy Molecules with Perturbed Excited-State Structure

We demonstrate and characterize Zeeman-Sisyphus (ZS) deceleration of a beam of ytterbium monohydroxide (YbOH). Our method uses a combination of large magnetic fields ($\sim$ 2.5 T) and optical spin-flip transitions to decelerate molecules while scattering only $\sim$ 10 photons per molecule. We study the challenges associated with the presence of internal molecular perturbations among the excited electronic states and discuss the methods used to overcome these challenges, including a modified ZS decelerator using microwave and optical transitions.

physics.atom-ph↗

arXiv2022

High-Resolution Laser Spectroscopy of a Functionalized Aromatic Molecule

We present a high-resolution laser spectroscopic study of the $\tilde{A}\,^2B_2- \tilde{X}\,^2A_1$ and $\tilde{B}\,^2B_1- \tilde{X}\,^2A_1$ transitions of calcium (I) phenoxide, CaOPh (CaOC$_6$H$_5$). The rotationally resolved band systems are analyzed using an effective Hamiltonian model and are accurately modeled as independent perpendicular ($b$- or $c$-type) transitions. The structure of calcium monophenoxide is compared to previously observed Ca-containing radicals and implications for direct laser cooling are discussed. This work demonstrates that functionalization of aromatic molecules with optical cycling centers can preserve many of the properties needed for laser-based control.

physics.atom-ph↗

arXiv2022

Pathway Towards Optical Cycling and Laser Cooling of Functionalized Arenes

Rapid and repeated photon cycling has enabled precision metrology and the development of quantum information systems using a variety of atoms and simple molecules. Extending optical cycling to structurally complex molecules would provide new capabilities in these areas, as well as in ultracold chemistry. Increased molecular complexity, however, makes realizing closed optical transitions more difficult. Building on the already established strong optical cycling of diatomic, linear triatomic, and symmetric top molecules, recent theoretical and experimental work has indicated that cycling will be extendable to phenol containing molecules, as well as other asymmetric species. The paradigm for these systems is the use of an optical cycling center bonded to a molecular ligand. Theory has suggested that cycling may be extended to even larger ligands, like naphthalene, pyrene and coronene. Here, we study the optical excitation and vibrational branching of the molecules CaO-2-naphthyl, SrO-2-naphthyl and CaO-1-naphthyl and find only weak decay to excited vibrational states, indicating a promising path to full quantum control and laser cooling of large arene-based molecules.

physics.atom-ph↗

arXiv2022

Functionalizing Aromatic Compounds with Optical Cycling Centers

Molecular design principles provide guidelines for augmenting a molecule with a smaller group of atoms to realize a desired property or function. We demonstrate that these concepts can be used to create an optical cycling center that can be attached to a number of aromatic ligands, allowing the scattering of many photons from the resulting molecules without changing the molecular vibrational states. We provide further design principles that indicate the ability to expand this work. This represents a significant step towards a quantum functional group, which may serve as a generic qubit moiety that can be attached to a wide range of molecular structures and surfaces.

physics.atom-ph↗

arXiv2022

Zeeman-Sisyphus Deceleration of Molecular Beams

We present a robust, continuous molecular decelerator that employs high magnetic fields and few optical pumping steps. CaOH molecules are slowed, accumulating at low velocities in a range sufficient for loading both magnetic and magneto-optical traps. During the slowing, the molecules scatter only 7 photons, removing around 8 K of energy. Because large energies can be removed with only a few spontaneous radiative decays, this method can be applied to nearly any paramagnetic atomic or molecular species, opening a general path to trapping of complex molecules.

physics.atom-ph↗

arXiv2021

Establishing a nearly closed cycling transition in a polyatomic molecule

We study optical cycling in the polar free radical calcium monohydroxide (CaOH) and establish an experimental path towards scattering $\sim$$10^4$ photons. We report rovibronic branching ratio measurements with precision at the $\sim10^{-4}$ level and observe weak symmetry-forbidden decays to bending modes with non-zero vibrational angular momentum. Calculations are in excellent agreement with these measurements and predict additional decay pathways. Additionally, we perform high-resolution spectroscopy of the $\widetilde{\text{X}}\,^2Σ^+(12^00)$ and $\widetilde{\text{X}}\,^2Σ^+(12^20)$ hybrid vibrational states of CaOH. These advances establish a path towards radiative slowing, 3D magneto-optical trapping, and sub-Doppler cooling of CaOH.

physics.atom-ph↗

arXiv2021

Accurate prediction and measurement of vibronic branching ratios for laser cooling linear polyatomic molecules

We report a generally applicable computational and experimental approach to determine vibronic branching ratios in linear polyatomic molecules to the $10^{-5}$ level, including for nominally symmetry forbidden transitions. These methods are demonstrated in CaOH and YbOH, showing approximately two orders of magnitude improved sensitivity compared with the previous state of the art. Knowledge of branching ratios at this level is needed for the successful deep laser cooling of a broad range of molecular species.

physics.atom-ph↗

arXiv2020

Observation and laser spectroscopy of ytterbium monomethoxide, YbOCH$_3$

We describe a laser spectroscopic study of ytterbium monomethoxide, YbOCH$_3$, a species of interest to searches for time-reversal symmetry violation using laser-cooled molecules. We report measurements of vibrational structure in the $\tilde{X}$ and $\tilde{A}$ states, vibrational branching ratios for several components of the $\tilde{A}$ state, and radiative lifetimes of low-lying electronic states. $\textit{Ab initio}$ calculations are used to aid the assignment of vibronic emission bands and provide insight into the electronic and vibrational structure. Our results demonstrate that rapid optical cycling is feasible for YbOCH$_3$, opening a path to orders-of-magnitude increased sensitivity in future measurements of P- and/or T-violating physics.

physics.atom-ph↗

arXiv2020

Direct Laser Cooling of a Symmetric Top Molecule

We report direct laser cooling of a symmetric top molecule, reducing the transverse temperature of a beam of calcium monomethoxide (CaOCH$_3$) to $1.8\pm0.7$ mK while addressing two distinct nuclear spin isomers. These results open a path to efficient production of ultracold chiral molecules and conclusively demonstrate that by using proper rovibronic optical transitions, both photon cycling and laser cooling of complex molecules can be as efficient as for much simpler linear species.

physics.atom-ph↗

arXiv2020

Franck-Condon tuning of optical cycling centers by organic functionalization

Laser induced electronic excitations that spontaneously emit photons and decay directly to the initial ground state ("optical cycling transitions") are used in quantum information and precision measurement for state initialization and readout. To extend this primarily atomic technique to organic compounds, we theoretically investigate optical cycling of alkaline earth phenoxides and their functionalized derivatives. We find that optical cycle leakage due to wavefunction mismatch is low in these species, and can be further suppressed by using chemical substitution to boost the electron withdrawing strength of the aromatic molecular ligand through resonance and induction effects. This provides a straightforward way to use chemical functional groups to construct optical cycling moieties for laser cooling, state preparation, and quantum measurement.

physics.atom-ph↗

arXiv2020

Branching ratios, radiative lifetimes and transition dipole moments for YbOH

Medium resolution ($Δν$ ~ 3 GHz) laser-induced fluorescence (LIF) excitation spectra of a rotationally cold sample of YbOH in the 17300-17950 cm$^{-1}$ range have been recorded using two-dimensional (excitation and dispersed fluorescence) spectroscopy. High resolution ($Δλ$ ~ 0.65 nm) dispersed laser induced fluorescence (DLIF) spectra and radiative decay curves of numerous bands detected in the medium resolution LIF excitation spectra were recorded. The vibronic energy levels of the $\tilde{X} \, ^2Σ^+$ state were predicted using a discrete variable representation approach and compared with observations. The radiative decay curves were analyzed to produce fluorescence lifetimes. DLIF spectra resulting from high resolution ($Δν$ < 10 MHz) LIF excitation of individual low-rotational lines in the $\tilde{A} \, ^2Π_{1/2}(0,0,0) - \tilde{X} \, ^2Σ^+(0,0,0)$, $\tilde{A} \, ^2Π_{1/2}(1,0,0) - \tilde{X} \, ^2Σ^+(0,0,0)$, $[17.73]Ω=0.5(0,0,0) - \tilde{X} \, ^2Σ^+(0,0,0)$ bands were also recorded. The DLIF spectra were analyzed to determine branching ratios which were combined with radiative lifetimes to obtain transition dipole moments. The implications for laser cooling and trapping of YbOH are discussed.

physics.atom-ph↗

arXiv2020

Molecular Asymmetry and Optical Cycling: Laser Cooling Asymmetric Top Molecules

We present a practical roadmap to achieve optical cycling and laser cooling of asymmetric top molecules (ATMs). Our theoretical analysis describes how reduced molecular symmetry, as compared to diatomic and symmetric non-linear molecules, plays a role in photon scattering. We present methods to circumvent limitations on rapid photon cycling in these systems. We calculate vibrational branching ratios for a diverse set of asymmetric top molecules and find that many species within a broad class of molecules can be effectively cooled with a manageable number of lasers. We also describe methods to achieve rotationally closed optical cycles in ATMs. Despite significant structural complexity, laser cooling can be made effective using extensions of the current techniques used for linear molecules. Potential scientific impacts of laser-cooled ATMs span frontiers in controlled chemistry, quantum simulation, and searches for physics beyond the Standard Model.

physics.atom-ph↗

arXiv2020

1D Magneto-Optical Trap of Polyatomic Molecules

We demonstrate a 1D magneto-optical trap of the polar free radical calcium monohydroxide (CaOH). A quasi-closed cycling transition is established to scatter $\sim 10^3$ photons per molecule, predominantly limited by interaction time. This enables radiative laser cooling of CaOH while compressing the molecular beam, leading to a significant increase in on-axis beam brightness and reduction in temperature from 8.4 mK to 1.4 mK.

physics.atom-ph↗