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S. C. Wright

Publications and source records attributed to S. C. Wright.

12 recordsLinked to original sources
arXiv2026

Non-stick vacuum wall collisions with a laser-coolable molecule

Molecular species that are suitable for direct laser cooling are typically considered lost or destroyed if they collide with an ambient temperature vacuum wall. Here, we study surface collisions with aluminum monofluoride (AlF), a laser-coolable molecule that survives this process with unusually high probability. We detect the outgoing AlF molecules from a single wall collision via Doppler-sensitive laser-induced fluorescence spectroscopy, using incoming supersonic (pulsed) and thermochemical (continuous) molecular beams. The angular, velocity and rovibrational level distributions of the outgoing molecules show near-complete thermalisation to the wall in a single collision event. We determine an upper limit to the surface residence time of about 5$~μ$s, and by monitoring the decay in density of pulses of molecules loaded into a small storage volume, we deduce the surface sticking probability for different materials. For a siloxane-coated metallic surface, the sticking probability of AlF is about 0.015, allowing us to accumulate molecules from the thermochemical source into an ambient temperature storage vessel at densities near $10^{8}~$cm$^{-3}$. This provides a route to compact, portable traps for neutral molecules.

physics.atom-ph↗
arXiv2026

Robust watt-level continuous-wave deep-ultraviolet lasers near 230 nm

Continuous-wave (CW) deep-ultraviolet (DUV) lasers near 230~nm enable laser cooling of AlF, Cd, and Zn, but second-harmonic generation below 237~nm relies in practice on beta-barium borate (BBO), whose walk-off and UV-induced degradation hinder sustained operation. We demonstrate compact, affordable VECSEL-based systems informed by four years of operating 14 DUV cavities in 12 laser systems across six European laboratories. External LBO cavities produce nearly 4~W at 463~nm with 94% cavity efficiency. We compare spherically and elliptically focused Brewster-cut BBO cavities with a normal-incidence AR-coated design. The AR-coated cavity delivers the highest power and efficiency, reaching 1.0~W at 51% cavity and 44% external efficiency; the spherical Brewster cavity reaches 700~mW and maintains constant circulating power over 70~h, while elliptical focusing reduces peak intensity sixfold and improves beam quality, albeit with greater alignment sensitivity. Collaboration-designed DUV optics, AlF spectroscopy, and Cd trapping validate the system.

physics.atom-ph↗
arXiv2025

Magneto-optical trapping of aluminum monofluoride

Magneto-optical trapping of molecules has thus far been restricted to molecules with $^2Σ$ electronic ground states. These species are chemically reactive and only support a simple laser cooling scheme from their first excited rotational level. Here, we demonstrate a magneto-optical trap (MOT) of aluminum monofluoride (AlF), a deeply bound and intrinsically stable diatomic molecule with a $^1Σ^+$ electronic ground state. The MOT operates on the strong A$^1Π\leftarrow{}$X$^1Σ^+$ transition near 227.5~nm, whose Q$(J)$ lines are all rotationally closed. We demonstrate a MOT of about $6\times 10^4$ molecules for the $J=1$ level of AlF, more than $10^4$ molecules for $J=2$ and $3$, and with no fundamental limit in going to higher rotational levels. Laser cooling and trapping of AlF is conceptually similar to the introduction of alkaline-earth atoms into cold atom physics, and is key to leveraging its spin-forbidden a$^3Π\leftarrow{}$X$^1Σ^+$ transition for precision spectroscopy and narrow-line cooling.

physics.atom-ph↗
arXiv2025

A large magneto-optical trap of cadmium atoms loaded from a cryogenic buffer gas beam

We demonstrate rapid loading of a magneto-optical trap (MOT) of cadmium atoms from a pulsed cryogenic helium buffer gas beam, overcoming strong photoionization losses. Using the $ ^1S_0 \rightarrow{} ^1P_1 $ transition at 229 nm, we capture up to $ 1.1(2) \times 10^7$ $^{112}$Cd atoms in 10 ms, achieving a peak density of $2.5 \times 10^{11}$cm$^{-3}$ and a phase-space density of $ 2 \times 10^{-9} $. The large scattering force in the deep ultraviolet enables Zeeman slowing within 5 cm of the trap, yielding a capture velocity exceeding 200 m/s. We measure the MOT trap frequency and damping constant, and determine the absolute photoionization cross section of the $^1P_1 $ state. Photoionization losses are mitigated via dynamic detuning of the trapping light's frequency, allowing efficient accumulation of multiple atomic pulses. Our results demonstrate the benefits of deep-UV (DUV) transitions and cryogenic beams for loading high-density MOTs, especially for species with significant loss channels in their main cooling cycle. The cadmium MOT provides a robust testbed that benchmarks our DUV laser cooling system and establishes the foundation for trapping and cooling polar AlF molecules, which share many optical and structural properties with Cd.

physics.atom-ph↗
arXiv2024

Reconciling mean-squared radius differences in the silver chain through improved measurement and {\it ab initio} calculations

Nuclear charge radius differences in the silver isotopic chain have been reported through different combinations of experiment and theory, exhibiting a tension of two combined standard errors. This study investigates this issue by combining high-accuracy calculations for six low-lying states of atomic silver with an improved measurement of the $5s ^2S_{1/2} - 5p ^2P_{3/2}$ transition optical isotope shift. Our calculations predict measured electronic transition energies in Ag I at the 0.3\% level, the highest accuracy achieved in this system so far. We calculate electronic isotope shift factors by employing analytical response relativistic coupled-cluster theory, and find that a consistent charge radius difference between $^{107,109}$Ag is returned when combining our calculations with the available optical isotope shift measurements. We therefore recommend an improved value for the mean-squared charge radius difference between $^{107}$Ag and $^{109}$Ag as $0.207(3)[4]$ fm$^2$, within one combined error from the value derived from muonic Ag experiments, and an updated set of charge radii differences across the isotopic chain.

physics.atom-ph↗
arXiv2023

Systematic errors arising from polarization imperfections in measurements of the electron's electric dipole moment

The electron's electric dipole moment (eEDM) can be determined by polarizing the spin of an atom or a molecule and then measuring the spin precession frequency in an applied electric field. Radiation is used to polarize the spin and then analyze the precession angle, and the measurement is often sensitive to the polarization of this radiation. We show how systematic errors can arise when both the polarization of the radiation and the magnitude of the electric field are imperfectly controlled. We derive approximate analytical expressions for these errors, confirm their accuracy numerically, and show how they can be corrected empirically. We consider spin manipulation using single-photon pulses, Raman pulses, and Stimulated Raman Adiabatic Passage (STIRAP), and show that STIRAP provides better immunity to these systematic errors. An experimental study of these errors partly supports our findings but also reveals another potential error that is not captured by this analysis.

physics.atom-ph↗
arXiv2022

Isotope Shifts in Cadmium as a Sensitive Probe for Physics Beyond the Standard Model

Isotope shifts (ISs) in atomic energy levels are sensitive probes of nuclear structure and new physics beyond the Standard Model. We present an analysis of the ISs of the cadmium atom (Cd I) and singly charged cadmium ion (Cd II). ISs of the 229 nm, 326 nm, 361 nm and 480 nm lines of Cd I are measured with a variety of techniques; buffer-gas-cooled beam spectroscopy, capturing atoms in a magneto-optic-trap, and optical pumping. IS constants for the D1 and D2 lines of Cd II are calculated with high accuracy by employing analytical response relativistic coupled-cluster theory in the singles, doubles and triples approximations. Combining the calculations for Cd II with experiments, we infer IS constants for all low-lying transitions in Cd I. We benchmark these constants as calculated via different many-body methods. Our calculations for Cd II enable nuclear charge radii of Cd isotopes to be extracted with unprecedented accuracy. The combination of our precise calculations and measurements shows that King Plots for Cd I can improve the state-of-theart sensitivity to a new heavy boson by up to two orders of magnitude.

physics.atom-ph↗
arXiv2022

The chemistry of AlF and CaF production in buffer gas sources

In this work, we explore the role of chemical reactions on the properties of buffer gas-cooled molecular beams. In particular, we focus on scenarios relevant to the formation of AlF and CaF via chemical reactions between the Ca and Al atoms ablated from a solid target in an atmosphere of a fluorine-containing gas, in this case, SF6 and NF3. Reactions are studied following an ab initio molecular dynamics approach, and the results are rationalized following a tree-shaped reaction model based on Bayesian inference. We find that NF3 reacts more efficiently with hot metal atoms to form monofluoride molecules than SF6. In addition, when using NF3, the reaction products have lower kinetic energy, requiring fewer collisions to thermalize with the cryogenic helium. Furthermore, we find that the reaction probability for AlF formation is much higher than for CaF across a broad range of temperatures.

physics.comp-ph↗
arXiv2022

Hyperfine resolved optical spectroscopy of the A$^2Π\leftarrow $X$^2Σ^+$ transition in MgF

We report on hyperfine-resolved laser spectroscopy of the A$^2Π\leftarrow $X$^2Σ^+$ transition of MgF, relevant for laser cooling. We recorded 25 rotational transitions with an absolute accuracy of better than 20 MHz, assigned 56 hyperfine lines and determined precise rotational, fine and hyperfine structure parameters for the A$^2Π$ state. The radiative lifetime of the A$^2Π$ state was determined to be 7.2(3) ns, in good agreement with \textit{ab initio} calculations. The transition isotope shift between bosonic isotopologues of the molecule is recorded and compared to predicted values within the Born-Oppenheimer approximation. We measured the Stark effect of selected rotational lines of the A$^2Π\leftarrow $X$^2Σ^+$ transition by applying electric fields of up to 10.6 kV cm$^{-1}$ and determined the permanent electric dipole moments of $^{24}$MgF in its ground X$^2Σ^+$ and first excited A$^2Π$ states to be $μ_X=$2.88(20) D and $μ_A=$3.20(22) D, respectively. Based on these measurements, we caution for potential losses from the optical cycling transition, due to electric field induced parity mixing in the excited state. In order to scatter $10^4$ photons, the electric field must be controlled to below 1 V cm$^{-1}$.

physics.atom-ph↗
arXiv2020

New techniques for a measurement of the electron's electric dipole moment

The electric dipole moment of the electron (eEDM) can be measured with high precision using heavy polar molecules. In this paper, we report on a series of new techniques that have improved the statistical sensitivity of the YbF eEDM experiment. We increase the number of molecules participating in the experiment by an order of magnitude using a carefully designed optical pumping scheme. We also increase the detection efficiency of these molecules by another order of magnitude using an optical cycling scheme. In addition, we show how to destabilise dark states and reduce backgrounds that otherwise limit the efficiency of these techniques. Together, these improvements allow us to demonstrate a statistical sensitivity of $1.8 \times 10^{-28}$ e cm after one day of measurement, which is 1.2 times the shot-noise limit. The techniques presented here are applicable to other high-precision measurements using molecules.

physics.atom-ph↗
arXiv2019

Microwave trap for atoms and molecules

We demonstrate a trap that confines polarizable particles around the antinode of a standing-wave microwave field. The trap relies only on the polarizability of the particles far from any resonances, so can trap a wide variety of atoms and molecules in a wide range of internal states, including the ground state. The trap has a volume of about 10 cm$^3$, and a depth approaching 1 K for many polar molecules. We measure the trap properties using $^{7}$Li atoms, showing that when the input microwave power is 610 W, the atoms remain trapped with a $1/e$ lifetime of 1.76(12) s, oscillating with an axial frequency of 28.55(5) Hz and a radial frequency of 8.81(8) Hz. The trap could be loaded with slow molecules from a range of available sources, and is particularly well suited to sympathetic cooling and evaporative cooling of molecules.

physics.atom-ph↗