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 K07: Cold and Ultracold Molecules I |
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Chair: Daniel McCarron, University of Connecticut Room: 206 B |
Wednesday, June 7, 2023 10:30AM - 10:42AM |
K07.00001: Creation of Ro-vibrational Ground State 6Li40K Molecules Canming He, Xiaoyu Nie, Anbang Yang, Victor A Avalos Pinilos, Sofia Botsi, Sunil Kumar, Kai Dieckmann We report on the creation of ground state 6Li40K molecules with an efficiency of 96%. The singlet stimulated Raman adiabatic passage (STIRAP) pathway is selected to transfer the ultracold 6Li40K molecules from the Feshbach state to X1Σ ro-vibrational ground state and |v ′ = 23〉 vibrational state of the unperturbed A1Σ + potential is chosen as the intermediate state. After applying a reverse STIRAP pulse, the ground state 6Li40K molecules are transferred back to the Feshbach state for detection by using absorptive imaging. The single-trip efficiency of 98% can be inferred by comparing the number of molecules before and after the round-trip STIRAP. The lifetime of the ground state molecules is measured to be around 6ms, which is limited by the two-body collision loss. An oscillation at the molecules' ground state has been observed during the lifetime measurement when all-atom species are trapped, and a possible explanation would be discussed. |
Wednesday, June 7, 2023 10:42AM - 10:54AM |
K07.00002: Microwave shielding of ultracold NaRb molecules Guanghua CHEN, Mucan Jin, Junyu Lin, Zhaopeng Shi, Bo Yang, Dajun Wang Recent years have witnessed tremendous progresses in creating and manipulating ultracold polar molecules. However, the two-body loss even without chemical reactions is still a hurdle for many future explorations. In this work, we investigate the loss suppression of bosonic NaRb molecules with a circular polarized microwave which can induce a long-range barrier via the resonant dipolar interaction and prevent molecules from reaching the short range and undergoing lossy collisions. We demonstrate suppression of the loss by over two orders of magnitude with the lowest two-body inelastic rate coefficient reaching 1×10^(-12) cm^3/s. The elastic-to-inelastic collision ratio is improved to around 1000, which should be enough for observing efficient evaporative cooling. |
Wednesday, June 7, 2023 10:54AM - 11:06AM |
K07.00003: Collisional shielding of a bosonic gas of polar molecules Jason S Rosenberg, Lysander Christakis, Ravin Raj, Zoe Z Yan, Youssef A Alaoui, Waseem S Bakr Degenerate gases of bosonic polar molecules are expected to possess a rich set of many-body phases enabled by their long-range dipolar interactions. However, evaporative cooling of these molecules to degeneracy has so far been hindered by rapid collisional losses in the bulk. Building off recent theoretical and experimental advances in the shielding of fermionic molecules with static electric fields, we demonstrate collisional shielding of bosonic NaRb molecules by using eight in-vacuum electrodes to generate a uniform electric field of 4.5 kV/cm. This field lies just above a resonance between two pairs of rotational states, resulting in a strongly repulsive collisional barrier at short-range. Here, we observe molecular lifetimes of several seconds in a bulk trap, consistent with one-body loss. Combined with the molecules' fast thermalization rate due to their –0.4 D dipole moment at the shielding electric field, this long lifetime presents a clear pathway to achieving a high phase space density Bose gas of NaRb through evaporative cooling. Moreover, by loading this gas into a 2D lattice, we hope to use our recently constructed molecular quantum gas microscope to probe the dipolar Bose-Hubbard model with single-site resolution. |
Wednesday, June 7, 2023 11:06AM - 11:18AM |
K07.00004: Field-linked resonances of polar molecules Xing-Yan Chen, Andreas Schindewolf, Sebastian Eppelt, Roman Bause, Marcel Duda, Shrestha Biswas, Tijs Karman, Timon A Hilker, Immanuel Bloch, Xin-Yu Luo We observed a novel type of scattering resonances related to "field-linked" bound states between two polar molecules. We use a microwave field addressing the J = 0 to J = 1 rotational transitions of the ground state NaK molecules to induce a long-range potential between the molecules. The interaction potential can be described by a van der Waals interaction plus a dipole-dipole interaction. The former shields the molecules against destructive short-range collisions, and together with the latter, hosts the "field-linked" bound states. We measured the resonance feature related to these bound states in both inelastic and elastic scattering, and observed orders of magnitude tunability over the collision rates. The field-linked resonance demonstrated here is universal and could be applied to a wide range of polar molecules, providing a general method to control the intermolecular interactions as well as to assemble ultracold polyatomic molecules. |
Wednesday, June 7, 2023 11:18AM - 11:30AM |
K07.00005: Progress towards higher phase space density of trapped SrF molecules Varun Jorapur, Thomas K Langin, Qian Wang, Geoffrey Zheng, David P DeMille For molecules, rotational closure of an optical cycling transition requires driving `Type-II' transitions, where the ground and excited state angular momenta (J and J' respectively) satisfy J ≥ J'. Such transitions exhibit sub-Doppler heating for red detuning, leading to warm (∼ 1 mK) and large (∼ 1 mm) magneto-optical traps (MOTs). Subsequent loading of optical dipole traps (ODTs), while subject to blue-detuned sub-Doppler cooling, is inefficient (∼ 5%) due to the small volume of the ODT relative to the MOT cloud. This sub-Doppler cooling is typically done after turning the magnetic field off. Here, we demonstrate that, if the magnetic field is left on, blue-detuned light of the correct polarization can also produce a strong confining force on the SrF molecules in our experiment. Switching from the `red-MOT' to this `blue-MOT' enables further cooling and compression, potentially leading to more efficient ODT loading. We also report a scheme for improved slowing of our SrF cryogenic molecular beam, leading to a factor of $sim 10$ increase in the number of trapped molecules in the MOT. This should provide sufficient density to observe SrF-SrF collisions in a bulk gas, which is a key step towards using collisional cooling to reach quantum degeneracy. |
Wednesday, June 7, 2023 11:30AM - 11:42AM |
K07.00006: Dynamics of a buffer-gas-loaded, deep optical trap for molecules Ashwin Singh, Lothar Maisenbacher, Ziguang Lin, Jeremy Axelrod, Cristian D Panda, Holger Müller Despite a diversity of interest in studying cold molecules, access to cold, trapped molecule samples has been limited to only a few select species. To this end, we here outline the design of an experiment aimed at trapping a variety of small, closed-shell molecules, such as N2, O2, CO, and HCl [1]. The molecules will be trapped at cryogenic temperatures by buffer-gas loading a deep optical dipole trap. The ~10 K trap depth will be produced by a tightly-focused, 1064-nm cavity capable of reaching intensities of hundreds of GW/cm2. Molecules will be directly buffer-gas loaded into the trap using a helium buffer gas at 1.5 K. The very far-off-resonant, quasi-electrostatic trapping mechanism is insensitive to a molecule’s internal state, energy level structure, and its electric and magnetic dipole moment. From our theoretical investigations of the trapping and loading dynamics, as well as the heating and loss rates, we conclude that 104–106 molecules are likely to be trapped. Our trap would open new possibilities in molecular spectroscopy, studies of cold chemical reactions, and precision measurement, amongst other fields of physics. |
Wednesday, June 7, 2023 11:42AM - 11:54AM |
K07.00007: Collisional Studies of Ultracold Ground-State NaCs Molecules Ian C Stevenson, Niccolò Bigagli, Claire Warner, Weijun Yuan, Siwei Zhang, Sebastian Will High loss rates have been a persistent barrier for quantum many-body experiments with ultracold molecules. The formation of collisional tetramer complexes and their subsequent excitation via trap light has been postulated as the dominant loss mechanism for samples of ultracold molecules. For some molecules (RbCs, KRb), such complexes have been observed and their lifetimes are in accordance with RRKM theory, while for others (NaK, NaRb) attempts to detect the complexes have failed. Given the many open questions regarding complex formation and lifetimes, the investigation of new molecular species is of particular importance. We report on collisional studies of ultracold NaCs molecules. With the ability to study samples of NaCs molecules in the absence of trap light for extended periods of time, our data excludes (NaCs)2 complex lifetimes below 100 ms, significantly longer than predicted by RRKM theory. We also study the temperature-dependence of molecule loss rates. Our investigation sheds light on the scattering properties of NaCs molecules and the validity of using statistical theories to describe the (NaCs)2 complex. |
Wednesday, June 7, 2023 11:54AM - 12:06PM |
K07.00008: Decoherence-free subspaces for quantum simulation and quantum information with ultracold RbCs molecules Philip D Gregory, Luke M Fernley, Albert Li Tao, Tom R Hepworth, Sarah L Bromley, Svetlana Kotochigova, Jeremy M Hutson, Simon L Cornish Ultracold polar molecules possess a rich network of rotational and hyperfine states that can be precisely coupled in experiments with resonant microwave fields. Engineering long-lived quantum coherences between rotational states is the crucial next step towards realising the full potential of ultracold molecules in current experiments. For molecules confined to optical traps, the rotational coherence time is typically limited by to the presence of large differential light shifts between the rotational states as a result of the anisotropic molecular polarizability. Here we present the successful development of a rotationally-magic optical trap that enables long rotational coherence times in a bulk gas of ultracold RbCs molecules. The trap is based around light at 1146nm detuned 168 GHz from a nominally forbidden X1Σ→b3Π vibronic transition, which allows tuning of the anisotropic component of the polarisability to zero. The trap is compatible with long molecule lifetimes, and the achievable coherence time is currently limited by the frequency stability of the trap laser; we estimate coherence times greater than 1s should be achievable for a laser frequency stabilised to less than 1 MHz. Using precision microwave spectroscopy over multiple rotational transitions, we show that the trap is near-magic for multiple rotational states at the same time. Motivated by this, we identify closed networks of quantum states in RbCs spanning multiple rotational levels that can be used to realise proposed schemes for quantum computing or novel synthetic dimensions for quantum simulation. Our approach for state selection is generally applicable to any bialkali molecule and is based upon the Python-based open source Diatomic-Py code developed by our group. |
Wednesday, June 7, 2023 12:06PM - 12:18PM |
K07.00009: Dynamics of itinerant quantum rigid rotors in 2D Reuben R Wang, John L Bohn Bulk gases of heteronuclear polar molecules provide a rich platform for explorations of many-body dipolar physics. One such example is the JILA KRb experiment, which has realized a degenerate Fermi gas by dipolar evaporation with DC electric field shielding in 2D. Having the electric field shut off, however, now presents us with a system of fully itinerant molecules where internal rotational states are changeable via dipole-dipole interactions. In this work, we formuate a semiclassical theory to investigate the dynamics resultant from this interplay of motional and internal rotational degrees of freedom. This permits us an understanding of rotational decoherence mechanisms within molecules that are initially prepared in nonentangled states of coherent superposition. |
Wednesday, June 7, 2023 12:18PM - 12:30PM |
K07.00010: An apparatus to create ultracold gases of bosonic and fermionic ground state NaK molecules Younghoon Lim, Jaeryeong Chang, Sungjun Lee, Yoonsoo Kim, Jee Woo Park Quantum gases of molecules with long-range, anisotropic dipolar interactions offer an exceptional platform to explore exotic quantum many-body physics, precision measurements, and quantum information processing. Here, we present an apparatus designed to produce ultracold gases of bosonic 23Na41K and fermionic 23Na40K molecules within a single experimental system. To this end, we demonstrate that 23Na, which is known to be an efficient sympathetic coolant for fermionic 40K, is also an effective coolant for bosonic 41K. A degenerate Bose-Bose mixture of 23Na-41K is created, and their Feshbach resonances are investigated, which serves as the starting point for the formation of their ground state molecules. Further experimental progress and outlook will be briefly discussed. |
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