Bulletin of the American Physical Society
54th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 68, Number 7
Monday–Friday, June 5–9, 2023; Spokane, Washington
Session Q07: Cold and Ultracold Molecules II |
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Chair: David Hvizdos, Purdue University Room: 206 B |
Thursday, June 8, 2023 8:00AM - 8:12AM |
Q07.00001: Observation of spin-rotation exchange in ultracold Rb + KRb collisions Yi-Xiang Liu, Lingbang Zhu, Mark Babin, Kang-Kuen Ni Studying atom-molecule collisional physics at ultracold temperature is essential for applications ranging from the sympathetic cooling of molecules to the Feshbach association of polyatomic molecules. Ultracold atom-molecule system also provides a new platform to study the chemistry in a new regime. In a previous work [1], we found that long-lived complexes are formed in Rb + KRb collisions, where Rb atoms are in the ground hyperfine state, and KRb molecules are in the rovibronic ground state. The complexes are photoexcited by the optical dipole trapping light, which explains the rapid atom-molecule loss observed in the samples. We recently found that with Rb prepared in the excited hyperfine state, very few complexes are detected in Rb + KRb collisions. Instead, we discovered that Rb atoms relax to the ground hyperfine state while exciting KRb molecules to rotationally excited states. We directly characterized the atom and molecule states after the collision using resonance-enhanced multi-photon ionization followed by time-of-flight mass spectrometry. Our results reveal a new loss mechanism in atom-molecule collisions and provide a benchmark for future theoretical calculations. |
Thursday, June 8, 2023 8:12AM - 8:24AM |
Q07.00002: Effects of vibrational and rotational excitation on the decay of cold trapped Rydberg NO molecules Matthew H Rayment, Stephen D Hogan The large static electric dipole moments of molecules in high Rydberg states allows efficient deceleration and trapping using inhomogeneous electric fields [1]. This has enabled, e.g., studies of slow Rydberg state decay processes [2], and ion-molecule reactions at temperatures <100 mK [3]. Here we describe the use of a cryogenically-cooled chip-based Rydberg-Stark decelerator, to electrostatically trap nitric oxide (NO) molecules in long-lived Rydberg states for up to 5 ms [4,5]. Trap decay rates were measured for molecules in Rydberg states with principal quantum numbers, n, between 32 and 50, in series converging to the N+ = 0 - 6 rotational states of the v+ = 0, and 1 vibrational states of NO+. For a given value of N+, similar decay time constants were measured for both vibrational series. However, these decay time constants do not follow the typical n-scaling of atomic Rydberg states. Instead they generally decrease as the value of n increases. This observation is attributed to the effects of vibrational channel interactions with short lived (~ 1 ps) low-n vibrationally excited states that lie close to v+ = 0 and 1 series limits. Furthermore, as N+ was increased the measured decay time constants decreased, because of the combined effects of an increased density of states and inherent predissociation. States in low-N+ series are of interest for ion-molecule reactions studies, with states in high-N+ series being important for trace gas sensing [6]. |
Thursday, June 8, 2023 8:24AM - 8:36AM |
Q07.00003: Towards internal and external sympathetic cooling of CaH+ Swapnil Patel, Jyothi Saraladevi, Kenneth R Brown The cooling of molecular ions to their internal and external ground state is crucial for many applications of trapped molecular ions. We are implementing a general method for cooling the external and internal degrees of freedom of the molecular ions using laser-cooled atomic ions and neutral atoms, respectively [1]. Our plan is to demonstrate this method with calcium mono-hydride ions (CaH+) using co-trapped and laser cooled calcium (40Ca+) ions and potassium (39K) atoms for sympathetic cooling. In our ion-atom hybrid trap [2], we can stably hold the three species together and control the chemical reactions between them. We have previously measured a slow charge exchange between Ca+ and K and were able to minimize the rate coefficient to (9.7 ± 3.9) x 10-11 cm3/s with 4% of Ca+ in the P1/2 state [3]. Recently, we have measured that the molecular ions (CaH+) whose motion is sympathetically cooled by atomic ions (Ca+) are stable in the presence of neutral atoms (39K). Our next step is to perform rotational spectroscopy of CaH+ using resonance enhanced multi-photon dissociation (REMPD) [4] to determine the internal molecular ion temperature. This will allow us to detect the cooling of the rotational motion of the molecular ions due to the interaction with the ultracold neutral atoms. |
Thursday, June 8, 2023 8:36AM - 8:48AM |
Q07.00004: Formation of ultra-cold 7Li4He molecules in a seeded supersonic jet Jeremy Glick, William Huntington, Daniel J Heinzen Van der Waals molecules containing helium have exceptionally low binding energies. For example, the 7Li4He dimer, which has been observed previously in buffer gas experiments,1 has a binding energy of the order of tens of milliKelvin. Here, we report on the observation of 7Li4He dimers in a seeded supersonic jet of helium. These are formed by three-body collisions 7Li + 4He + 4He → 7Li4He + 4He, and detected with laser-induced fluorescence on the A2Π(v') ← X2Σ+(v''=0) transitions, with v' = 5 and 6. In contrast to previous work, the 7Li4He dimers are ultracold, with a temperature of 10 mK. As such, this method opens up a possible route to studies of molecular formation and collisions in the 1 mK to 100 mK temperature range, intermediate between the sub-mK or above 100 mK temperatures of most previous work. We are also investigating the origin of additional spectral features that are observed to the red of the bound-bound transitions, and carrying out an analysis of the formation rate of the dimers in the helium jet. |
Thursday, June 8, 2023 8:48AM - 9:00AM |
Q07.00005: Towards direct laser cooling of barium monofluoride Felix Kogel, Marian Rockenhäuser, Einius Pultinevicius, Tim Langen We report on an experiment aimed at direct laser cooling of BaF molecules for applications in cold chemistry and precision tests of fundamental symmetries. In an effort to realize such cooling, we have performed high-resolution absorption spectroscopy of the lowest rovibrational states. This has allowed us to characterize the cooling and repumping transitions for laser cooling, as well as to realize near background-free fluorescence imaging of a cold molecular beam. In addition to the experimental effort, we will present our theoretical progress in realizing efficient Doppler, sub-Doppler and coherent cooling schemes for both bosonic and fermionic isotopologues of BaF. |
Thursday, June 8, 2023 9:00AM - 9:12AM |
Q07.00006: Progress towards laser cooling of AlCl Boerge Hemmerling, Chen Wang, Li-Ren Liu, John R Daniel, Madhav Dhital, Chris Bardeen Novel applications for ultracold polar molecules include studies of many-body physics of quantum degenerate gases, quantum computing, precision measurements and tests of fundamental symmetries. Confining molecules in a magneto-optical trap is an ideal first step to apply subsequent cooling and trapping schemes to create an ultracold sample of molecules. While this approach has been used extensively with atoms, applying the same to molecules is challenging due to the presence of dark states which interrupt the photon cycle process. At present, a number of molecules has been identified to be suitable for laser cooling with AlCl being an excellent candidate with Franck-Condon factors of 99.88%. We produce a beam of AlCl via pulsed-laser ablation of a KCl:Al mixture target in a cryogenic buffer-gas beam source. Here, we will report on our progress towards applying laser slowing and cooling to the beam and discuss our theoretical model of the expected magneto-optical trap forces of AlCl. Furthermore, we will give an update on our setup to deposit and study thin films of AlCl, which could provide high-yield ablation precursors. |
Thursday, June 8, 2023 9:12AM - 9:24AM |
Q07.00007: Rovibrational optical cooling performed by broadband multimode diode laser in a Rb2 supersonic beam Manuel A Lefran Torres, David Rodriguez Fernandez, Marcos R Cardoso, Olivier Dulieu, Nadia Bouloufa-Maafa, Luis G Marcassa In this work, we have investigate optical rovibrational cooling of Rb2 molecules in a thermal supersonic beam. Broadband multimode diode lasers were spectrally shaped using a 4F grating configuration, in order to performed optical transitions from X1Σg+ ground state to the B1Πu excited potential in the 680-700 nm range. The optical shaping system is composed of a high efficiency transmission grating, a cylindrical lens and a digital micromirror device (DMD), which presents a theoretical resolution of 0.6 cm-1. The molecules were detected by photoionization technique, through transitions from the X1∑g+ → B1Πu using a pulsed dye laser at 682 nm, and then photoionized by a 532 nm pulsed laser 5 ns later. The results indicate that we are able to pump most of the molecules to vX=0, JX≤10 using an appropriated optical shaping. Spectroscopy of the 21Σu+ was also performed in the 480 nm range, using this cold rovibrational sample. Simulations indicate that the optical pumping results should be improved by applying a virtually imaged phased array system. |
Thursday, June 8, 2023 9:24AM - 9:36AM |
Q07.00008: Laser spectroscopy of aromatic molecules with optical cycling centers: strontium (I) phenoxides Guanming Lao, Guo-Zhu Zhu, Claire Dickerson, Benjamin Augenbraun, Anastassia Alexandrova, Justin R Caram, Eric R Hudson, Wesley C Campbell 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. |
Thursday, June 8, 2023 9:36AM - 9:48AM |
Q07.00009: Theoretical Investigation of CaH Formation in a Buffer Gas Cell Rian Koots, Jesus Perez Rios Calcium monohydride (CaH) has proved to be a viable candidate for laser cooling and was justified for further study as a potential pathway to produce ultracold hydrogen [1]. Efficient formation of CaH is non-trivial, and the current method for doing so is via laser ablation of solid CaH2 [2]. However, CaH formation through a chemical reaction in a buffer gas cell leads to a more stable CaH production and thus a more desirable experimental protocol. In this work, we calculate the rate of CaH formation when Ca atoms are scattered with H2 molecules, and its dependence on initial H2 rovibrational energies. A quasi-classical trajectory (QCT) method is used to simulate these trajectories [3], and CaH formation rates are calculated as a function of collision energy and initial rovibrational state of H2. As a result, we find that it could be beneficial to excite H2 to higher vibrational states via an intermediate electronic state to boost the production of CaH molecules. These results may serve as experimental motivation for the efficient formation of CaH for further study. |
Thursday, June 8, 2023 9:48AM - 10:00AM |
Q07.00010: Diatomic molecules of alkali-metal and alkaline-earth metal atoms: interaction potentials, dipole moments, and polarizabilities Hela Ladjimi, Michal Tomza Ultracold diatomic molecules find application in quantum studies ranging from controlled chemistry and precision measurement physics to quantum many-body simulation and potentially quantum computing. Accurate knowledge of molecular properties is required to guide and explain ongoing experiments. |
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