Enhanced molecular yield from a cryogenic buffer gas beam source via excited state chemistry

We use narrow-band laser excitation of Yb atoms to substantially enhance the brightness of a cold beam of YbOH, a polyatomic molecule with high sensitivity to physics beyond the standard model (BSM). By exciting atomic Yb to the metastable ³P₁ state in a cryogenic environment, we significantly increase the chemical reaction cross-section for collisions of Yb with reactants. We characterize the dependence of the enhancement on the properties of the laser light, and study the final state distribution of the YbOH products. The resulting bright, cold YbOH beam can be used to increase the statistical sensitivity in searches for new physics utilizing YbOH, such as electron electric dipole moment and nuclear magnetic quadrupole moment experiments. We also perform new quantum chemical calculations that confirm the enhanced reactivity observed in our experiment and compare reaction pathways of Yb(³P) with the reactants H₂O and H₂O₂. More generally, our work presents a broad approach for improving experiments that use cryogenic molecular beams for laser cooling and precision measurement searches of BSM physics

Direct measurement of high-lying vibrational repumping transitions for molecular laser cooling

Molecular laser cooling and trapping requires addressing all spontaneous decays to excited vibrational states that occur at the $\gtrsim 10^{-4} - 10^{-5}$ level, which is accomplished by driving repumping transitions out of these states. However, the transitions must first be identified spectroscopically at high-resolution. A typical approach is to prepare molecules in excited vibrational states via optical cycling and pumping, which requires multiple high-power lasers. Here, we demonstrate a general method to perform this spectroscopy without the need for optical cycling. We produce molecules in excited vibrational states by using optically-driven chemical reactions in a cryogenic buffer gas cell, and implement frequency-modulated absorption to perform direct, sensitive, high-resolution spectroscopy. We demonstrate this technique by measuring the spectrum of the $\tilde{A}^2\Pi_{1/2}(1,0,0)-\tilde{X}^2\Sigma^+(3,0,0)$ band in $^{174}$YbOH. We identify the specific vibrational repump transitions needed for photon cycling, and combine our data with previous measurements of the $\tilde{A}^2\Pi_{1/2}(1,0,0)-\tilde{X}^2\Sigma^+(0,0,0)$ band to determine all of the relevant spectral constants of the $\tilde{X}^2\Sigma^+(3,0,0)$ state. This technique achieves high signal-to-noise, can be further improved to measure increasingly high-lying vibrational states, and is applicable to other molecular species favorable for laser cooling.Comment: 14 pages, 5 figure

Enhanced molecular yield from a cryogenic buffer gas beam source via excited state chemistry

We use narrow-band laser excitation of Yb atoms to substantially enhance the brightness of a cold beam of YbOH, a polyatomic molecule with high sensitivity to physics beyond the standard model (BSM). By exciting atomic Yb to the metastable ³P₁ state in a cryogenic environment, we significantly increase the chemical reaction cross-section for collisions of Yb with reactants. We characterize the dependence of the enhancement on the properties of the laser light, and study the final state distribution of the YbOH products. The resulting bright, cold YbOH beam can be used to increase the statistical sensitivity in searches for new physics utilizing YbOH, such as electron electric dipole moment and nuclear magnetic quadrupole moment experiments. We also perform new quantum chemical calculations that confirm the enhanced reactivity observed in our experiment and compare reaction pathways of Yb(³P) with the reactants H₂O and H₂O₂. More generally, our work presents a broad approach for improving experiments that use cryogenic molecular beams for laser cooling and precision measurement searches of BSM physics

The pure rotational spectrum of YbOH

The pure rotational spectrum of YbOH has been recorded and analyzed to produce fine and magnetic hyperfine parameters for the X^2Σ^+(0,0,0) state. These parameters are compared with those determined from the optical study [Melville and Coxon, J. Chem. Phys.115, 6974-6978 (2001)] and with the values for YbF [Dickinson et al.115, 6979-6989 (2001)]. The results support the existence of an unobserved perturbing state near the A^2Π_(1/2) state, similar to that previously found in YbF. The precisely determining parameters lays the foundation for laser cooling YbOH, which will aid in the search for new physics beyond the standard model

Récits d’engagement

We use narrow-band laser excitation of Yb to substantially enhance the brightness of a cold beam of YbOH, a polyatomic molecule with high sensitivity to physics beyond the Standard Model (BSM). By exciting atomic Yb to the metastable ³P₁ state in a cryogenic environment, we significantly increase the chemical reaction cross-section for collisions of Yb with reactants. We characterize the dependence of the enhancement on the properties of the laser light, and study the final state distribution of the YbOH products. The resulting bright, cold YbOH beam can be used to increase the statistical sensitivity in searches for new physics utilizing YbOH, such as electron electric dipole moment (eEDM) and nuclear magnetic quadrupole moment (NMQM) experiments. We also perform new quantum chemical calculations that confirm the enhanced reactivity observed in our experiment. Additionally, our calculations compare reaction pathways of Yb(³P) with the reactants H₂O and H₂O₂. More generally, our work presents a broad approach for improving experiments that use cryogenic molecular beams for laser cooling and precision measurement searches of BSM physics

Simulations of a frequency-chirped magneto-optical trap of MgF

We simulate the capture process of MgF molecules into a frequency-chirped molecular MOT. Our calculations show that by chirping the frequency, the MOT capture velocity is increased by about of factor of 4 to 80 m/s, allowing for direct loading from a two-stage cryogenic buffer gas beam source. Moreover, we simulate the effect of this frequency chirp for molecules already present in the MOT. We find that the MOT should be stable with little to no molecule loss. The chirped MOT should thus allow loading of multiple molecule pulses to increase the number of trapped molecule

Characterizing the fundamental bending vibration of a linear polyatomic molecule for symmetry violation searches

Polyatomic molecules have been identified as sensitive probes of charge-parity violating and parity violating physics beyond the Standard Model (BSM). For example, many linear triatomic molecules are both laser-coolable and have parity doublets in the ground electronic $\tilde{X} {}^2\Sigma^+ (010)$ state arising from the bending vibration, both features that can greatly aid BSM searches. Understanding the $\tilde{X} {}^2\Sigma^+ (010)$ state is a crucial prerequisite to precision measurements with linear polyatomic molecules. Here, we characterize the fundamental bending vibration of ${}^{174}$ YbOH using high-resolution optical spectroscopy on the nominally forbidden $\tilde{X} {}^2\Sigma^+ (010)$ ${}\rightarrow{}\tilde{A}{}^2\Pi_{1/2}(000)$ transition at 588 nm. We assign 39 transitions originating from the lowest rotational levels of the $\tilde{X} {}^2\Sigma^+ (010)$ state, and accurately model the state’s structure with an effective Hamiltonian using best-fit parameters. Additionally, we perform Stark and Zeeman spectroscopy on the $\tilde{X} {}^2\Sigma^+ (010)$ state and fit the molecule-frame dipole moment to $D_\mathrm{mol} = 2.16(1)$ D and the effective electron g -factor to $g_S = 2.07(2)$ . Further, we use an empirical model to explain observed anomalous line intensities in terms of interference from spin–orbit and vibronic perturbations in the excited $\tilde{A}{}^2\Pi_{1/2}(000)$ state. Our work is an essential step toward searches for BSM physics in YbOH and other linear polyatomic molecules