Bulletin of the American Physical Society
52nd Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics
Volume 66, Number 6
Monday–Friday, May 31–June 4 2021; Virtual; Time Zone: Central Daylight Time, USA
Session M08: Laser Cooling of MoleculesLive
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Chair: Boerge Hemmerling, UC Riverside |
Wednesday, June 2, 2021 2:00PM - 2:12PM Live |
M08.00001: A Concept for Laser Cooling of Carbon Dimers Niccolò Bigagli, Daniel W Savin, Sebastian Will While carbon plays an ubiquitous role in physics, chemistry, engineering, biology, and medicine, methods to achieve quantum control over carbon are not as developed as for other species. Direct laser cooling of atomic carbon is hard as the relevant transitions are located in the VUV. Here, we present a concept for laser cooling of 12C dimers. C2 has a relatively simple level scheme due to its large vibrational spacings, vanishing nuclear spin, and weak spin orbit coupling that minimizes singlet-triplet mixing. C2 offers several potential transition bands for laser cooling in accessible wavelength ranges. We discuss the characteristics of these bands, their suitability for laser cooling, and technical implications for laser cooling schemes. We find that laser cooling of C2 is within reach, requiring a technical complexity comparable to existing laser cooling setups for molecules. |
Wednesday, June 2, 2021 2:12PM - 2:24PM Live |
M08.00002: Laser Cooling of CaH Molecules Sebastian Vazquez-Carson, Qi Sun, Tanya Zelevinsky We present experimental results that lead to the transverse laser cooling of a cryogenic beam of CaH molecules via the Doppler and Sisyphus mechanisms. We investigate the relevant molecular structure through in-cell absorption spectroscopy and high resolution in-beam spectroscopy, and discuss the experimental apparatus necessary to effectively cool CaH. We compare and contrast the requirements and obstacles arising from cooling on the ΧΣ-ΒΣ transition versus the ΧΣ-AΠ transition. We also compare the experimentally measured vibrational branching ratios (f00, f01,f02) of the two cooling states to their theoretically predicted values and discuss how to close vibrational loss channels in the cycling scheme. Finally, we discuss laser cooling of CaH molecules as we progress towards a MOT, and, in the future, dissociation of CaH and creation of a trapped ultracold gas of hydrogen atoms. |
Wednesday, June 2, 2021 2:24PM - 2:36PM Live |
M08.00003: Spectroscopy for Laser Cooling and Trapping of AlCl John R Daniel, Chen Wang, Taylor Lewis, Alexander Teplukhin, Brian K Kendrick, Chris Bardeen, Shan-Wen Tsai, Boerge Hemmerling Cooling atoms to the ultracold regime has allowed for studies of physics, ranging from many-body physics of quantum degenerate gases, quantum computing, precision measurements and tests of fundamental symmetries. Extending these experiments to polar molecules has the prospect of enhancing the sensitivity of such tests and of enabling novel studies, such as cold controlled chemistry. However, applying traditional laser cooling techniques to molecules is rendered difficult due to their additional degrees of freedom which result in a limited photon scattering budget. Here we study aluminum monochloride (AlCl) as a promising candidate for laser cooling and trapping. We use a frequency-tripled (SHG + SFG) Titanium-Sapphire laser and generate AlCl via laser ablation of various precursors in a cryogenic helium buffer gas beam source. We discuss our spectroscopy measurements of the laser cooling line, our estimates for the Franck-Condon factor of the ν = 0 → ν' = 0 transition and ab-intio calculations of the potential energy surfaces of the X1Σ+ and A1Π states. Additionally, we discuss AlCl precursor study results, and progress towards implementing laser cooling. |
Wednesday, June 2, 2021 2:36PM - 2:48PM Live |
M08.00004: Buffer gas cooling, optical cycling and radiative deflection of AlF molecules Simon Hofsaess, Maximilian J Doppelbauer, Sidney Wright, Sebastian Kray, Boris Sartakov, Jesús Pérez-Ríos, Gerard Meijer, Stefan Truppe Aluminum monofluoride (AlF) is a promising candidate for a high-density magneto-optical trap (MOT) of molecules. Here, we show that AlF can be produced efficiently in a bright, pulsed cryogenic buffer gas beam, and demonstrate rapid optical cycling on the Q rotational lines of the A1Π↔X1Σ+ transition. We measure the brightness of the molecular beam to be >1012 molecules per steradian per pulse in a single rotational state and present a new method to determine its velocity distribution accurately in a single molecular pulse. The photon scattering rate is measured using three different methods and compared to theoretical predictions of the optical Bloch equations and a rate equation model. An exceptionally high scattering rate of up to 42(7) x 106 s-1 can be sustained despite the large number of Zeeman sublevels (up to 216 for the Q(4) transition) involved in the optical cycle. We demonstrate that losses from the optical cycle due to vibrational branching to X1Σ+, v=1 can be addressed efficiently with a repump laser, allowing us to scatter about 104 photons using two lasers. Further, we investigate two other loss channels, photo-ionization and parity mixing by stray electric fields. The upper bounds for these effects are sufficiently low to allow loading the molecules into a MOT. |
Wednesday, June 2, 2021 2:48PM - 3:00PM Live |
M08.00005: Polarization enhanced cooling of SrF molecules in a deep Optical Dipole Trap Thomas K Langin, Varun Jorapur, Yuqi Zhu, Qian Wang, David P DeMille Creating quantum degenerate molecular gases by `direct' cooling and trapping of molecules (as opposed to assembly from ultracold atoms), once a far-off dream, now seems like a very realistic goal. One step towards achieving this dream is demonstrating the ability to load molecules into conservative traps, such as optical dipole traps (ODTs), while retaining very cold temperatures. We demonstrate that, by choosing optimal polarizations of the ODT laser and of intensity imbalanced counter-propagating $\Lambda$-enhanced gray molasses lasers, we can load SrF molecules with temperatures as low as 10$\mu$K into a 420$\mu$K deep ODT. Unlike alkali atoms, SrF molecules in the $X^{2}\Sigma_{1/2}$ state have tensor and vector polarizabilities, so a dependence on ODT polarization was expected. However, the interplay between the polarization of the ODT and the $\Lambda$-cooling light, and the intensity imbalance of the latter, was unexpected, and requires further exploration. Using this technique, we have loaded $\sim 4$\% of the $N\sim 4000$ SrF molecules trapped in our rfMOT and reached densities of $6.5\times 10^{8}$\,cm$^{-3}$. We are currently working on techniques for loading more molecules and for further cooling of SrF. |
Wednesday, June 2, 2021 3:00PM - 3:12PM Live |
M08.00006: Ultracold YO Molecules in an Optical Lattice Justin Burau, Kameron Mehling, Yewei Wu, Shiqian Ding, Jun Ye Dense ultracold molecular samples are media to explore rich physics ranging from cold chemistry, quantum information science, and precision measurement of fundamental physics. In this talk, I will report our current progress on achieving a dense ultracold molecular sample by loading more than 103 ultracold YO molecules in an optical lattice. We demonstrate robust cooling in the lattice, realizing μK temperatures and record phase space density for laser cooled molecules at 3×10−6. |
Wednesday, June 2, 2021 3:12PM - 3:24PM Live |
M08.00007: Laser slowing towards a 3D MOT of CaOH molecules Nathaniel Vilas, Christian Hallas, Loic Anderegg, Benjamin Augenbraun, Louis Baum, Debayan Mitra, John M Doyle Polyatomic molecules represent a new frontier in AMO physics, promising a number of new scientific opportunities in areas ranging from quantum simulation to ultracold chemistry to precision measurement. Laser cooling techniques have successfully brought several species of diatomic molecules to ultracold temperatures in the past several years, and have recently been extended to the polyatomic molecules SrOH, YbOH, CaOH, and CaOCH3. Despite this success, in all cases to date laser cooling was performed in one dimension, which required scattering fewer than 1000 photons. The next step in our path towards laser-cooled, ultracold polyatomic molecules is to capture them in a 3D magneto-optical trap (MOT). Here, we report on progress towards this goal with CaOH. A laser cooling scheme capable of scattering more than 10,000 photons is identified and tested, enabling us to demonstrate radiative slowing to near the MOT capture velocity. |
Wednesday, June 2, 2021 3:24PM - 3:36PM Live |
M08.00008: Polyatomic molecules with multivalent optical cycling centers Phelan Yu, Adrian Lopez, William Goddard III, Nicholas Hutzler Direct laser cooling and trapping of polyatomic molecules promise new opportunities in precision metrology, quantum information, many-body physics, and fundamental chemistry. Contemporary experimental and theoretical efforts have mostly focused on cycling photons via a single sσ electron localized to an alkaline earth-like metal center. Here, we report new pathways for laser cooling polyatomic molecules with multiple cycling electrons hosted by post-transition metal and metalloid centers (i.e. Al, Si, P). We have characterized the electronic structure and rovibrational branching of several prototypical candidates using ab initio quantum chemical methods, finding quasi-closed photon cycling schemes with highly diagonal, visible-wavelength transitions. In the process, we have identified new heuristics for engineering laser-coolable polyatomic molecules with higher metal valences. Our findings help elucidate the interplay between hybridization, repulsion, and ionicity in optically active species and provide a roadmap towards using laser-coolable molecules with complex electronic structure as a resource for quantum science and measurement. |
Wednesday, June 2, 2021 3:36PM - 3:48PM Live |
M08.00009: Accurate prediction of vibronic levels and branching ratios for laser-coolable linear polyatomic molecules Chaoqun Zhang, Lan Cheng We report a generally applicable computational scheme to calculate vibronic levels and branching ratios for laser-coolable linear polyatomic molecules to an accuracy and completeness to be useful to guide experimental studies. The present computational scheme consists of a multi-state quasidiabatic Hamiltonian with relevant spin-vibronic perturbations, coupled-cluster calculations for adiabatic potential energy surfaces, and discrete variable representation calculations for vibronic levels and wave functions. The computed vibronic levels and branching ratios for the A2Π1/2 → X2Σ1/2 transitions of CaOH, SrOH, and YbOH show promising agreement with the experimental measurements. The calculations elucidate intensity borrowing mechanisms for the nominally symmetry-forbidden transitions. Based on the computed branching ratios, laser-cooling SrOH requires fewer repumping lasers than CaOH. A close inspection of computational results further reveals it beneficial to avoid Fermi resonances in designing laser-coolable molecules. |
Wednesday, June 2, 2021 3:48PM - 4:00PM On Demand |
M08.00010: Towards Transversal Laser Cooling of Barium Monofluoride Marian Rockenhäuser Cold molecular gases are the starting point for many novel and interdisciplinary applications ranging from few- and many-body physics to cold chemistry and precision measurements. In particular, heavy polar molecules, such as barium monofluoride (BaF), are promising candidates for tests of fundamental symmetries and studies of quantum systems with strong, long-range interactions. Here we report on our progress towards transversal cooling of an intense beam of such BaF molecules and discuss strategies for their further cooling. |
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