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 X08: Collisions, Reactions, and Field Control of Cold and Ultracold MoleculesLive
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Chair: Timur Tscherbul, University of Nevada, Reno |
Friday, June 4, 2021 8:00AM - 8:12AM Live |
X08.00001: A simple model of the electric field dependence of complex-dominated ultracold molecular collisions Goulven Quéméner, James Croft, John L Bohn Recent experiments on bosonic NaRb [1, 2], RbCs [3] and fermionic NaK [4] molecules have observed high losses of non-reactive ultracold ground state molecules undergoing two-body collisions. A lot of theoretical effort has been devoted to understand this kind of loss mechanism, believed to originate from the formation of a tetramer complex at short-range. Using a recent unified formalism [5] that compiles average cross sections, random matrix and quantum defect theories, these losses of molecules can be characterized by a specific coefficient x, which can be linked to a short-range apparent loss probability p. When p ≈ 1, the loss is said to be universal and when p < 1, the loss is said to be non-universal. Experimentally, it is found that, while at zero electric field the collisions are non-universal [1, 3, 4, 6], they quickly become universal upon applying a small electric field [2,4]. We present a simple model of this phenomenon [7], showing that p can go from a value different than 1 to a value near 1 as an electric field is turned on. |
Friday, June 4, 2021 8:12AM - 8:24AM Live |
X08.00002: Metrological prospects for ultracold $^{88}{Sr}_2$ molecules in the absolute rovibrational ground state Emily Tiberi, Kon H Leung, Brandon Iritani, Tanya Zelevinsky We report on the successful creation of an ultracold sample of ground-state $^{88}{Sr}_2$ molecules. This demonstrates important progress toward an ultracold strontium molecular clock for metrology and precision measurements. Molecules are transferred from the most-weakly bound vibrational level of the ground potential to the absolute ground state via low-lying vibrational states in the $(1)0_{u}^{+}$ excited state using a counterintuitive STIRAP pulse scheme. In addition, we have identified prospective far-off-resonant “magic” lattice wavelengths in the mid-IR, - wavelengths for which the differential polarizability between two clock states vanishes. These potential magic values occur for deeply bound ground rovibrational states and offer attractive prospects for long-lived coherent superpositions of clock states for the study of variations of fundamental constants and fifth-force measurements. |
Friday, June 4, 2021 8:24AM - 8:36AM Live |
X08.00003: Robust storage qubits in ultracold RbCs molecules Philip Gregory, Jacob Blackmore, Sarah L Bromley, Jeremy Hutson, Simon L Cornish Quantum states with long-lived coherence are essential for quantum computation, simulation and metrology. The nuclear spin states of ultracold molecules prepared in the singlet rovibrational ground state are an excellent candidate for encoding and storing quantum information. However, it is important to understand all sources of decoherence for these qubits, and then eliminate them, in order to reach the longest possible coherence times. Here, we fully characterise the dominant mechanisms for decoherence of a storage qubit in an optically-trapped ultracold gas of RbCs molecules using high-resolution Ramsey spectroscopy. Guided by a detailed understanding of the hyperfine structure of the molecule, we tune the magnetic field to where a pair of hyperfine states have the same magnetic moment. These states form a qubit, which is insensitive to variations in magnetic field. Our experiments reveal an unexpected differential tensor light shift between the states, caused by weak mixing of rotational states. We demonstrate how this light shift can be eliminated by setting the angle between the linearly polarised trap light and the applied magnetic field to a magic angle of arccos(1/√3) ≈ 54.7°. This leads to a coherence time exceeding 6.9 s (90% confidence level). Our results unlock the potential of ultracold molecules as a platform for quantum computation. |
Friday, June 4, 2021 8:36AM - 8:48AM Live |
X08.00004: Controlling ultracold molecular reactions through nuclear spins Lingbang Zhu, Matthew A Nichols, Yu Liu, Ming-Guang Hu, Yi-Xiang Liu, Kang-Kuen Ni Controlling the quantum states of reactive systems has enabled the study of underlying interaction potentials and the alteration of reaction rates. However, control over the quantum states of reaction outcomes has remained challenging. In this talk, I discuss our recent work which utilizes the nuclear spin states of ultracold KRb reactant molecules prepared in their rovibronic ground state to control the quantum states of products formed through the reaction 2KRb → K2 + Rb2. This newly demonstrated form of control relies on the conservation of nuclear spin throughout the reaction. [Nat. Chem. https://doi.org/10.1038/s41557-020-00610-0 (2020)] Specifically, by performing resonance-enhanced multiphoton ionization spectroscopy, we find that the products retain the reactants’ nuclear spins almost perfectly, which is manifested as a strong parity preference for the rotational quantum states of the products. By applying an external magnetic field to change the initial nuclear spin state of the reactants, we then observe that the relative population in different product quantum states can be altered. These techniques could enable the study of quantum entanglement between reaction products. |
Friday, June 4, 2021 8:48AM - 9:00AM Live |
X08.00005: Precision test of statistical dynamics with state-to-state ultracold chemistry Matthew A Nichols, Yu Liu, Ming-Guang Hu, Lingbang Zhu, Yi-Xiang Liu, Kang-Kuen Ni Chemical reactions between quantum-state-controlled molecules at ultralow temperatures provide an ideal platform for testing state-of-the-art quantum chemistry and scattering calculations. In this talk, I will discuss our recent measurements of the complete product quantum state distribution for the exchange reaction 2KRb → K2 + Rb2, where the ultracold KRb reactants are prepared in their rovibronic ground state. By combining state-selective photoionization with ion velocity-map imaging, we perform state-resolved coincident detection of the reaction products. In this way, we measure the scattering probabilities for all 57 rotational state-pairs that are allowed by the reaction exoergicity. Our results exhibit reasonable agreement with a state-counting model based on statistical theory, but also reveal several state-pairs which show significant deviations. Specifically, we observe a highly suppressed scattering probability for the state-pair closest to the exoergicity limit, a result of the long-range potential inhibiting the escape of products. |
Friday, June 4, 2021 9:00AM - 9:12AM Live |
X08.00006: Scattering length from accurate ab initio interaction potential of the NaLi molecule in the a3Σ+ electronic state Marcin Gronowski, Adam M Koza, Michal Tomza Ultracold polar and magnetic 23Na6Li molecules in the rovibrational ground state of the lowest triplet a3Σ+ electronic state have been recently produced [1,2]. Here, we present the calculation of the electronic and rovibrational structure of these 14-electron molecules with spectroscopic accuracy (<0.5 cm-1) using state-of-the-art ab initio methods of quantum chemistry [3]. We employ the hierarchy of the coupled-cluster wave functions and Gaussian basis sets extrapolated to the complete basis set limit. We show that the inclusion of higher-level excitations, core-electron correlation, relativistic, QED, and adiabatic corrections is necessary to reproduce accurately the scattering and spectroscopic properties of alkali-metal systems. We obtain the well depth, De=229.9(5) cm-1, the dissociation energy, D0=208.2(5) cm-1, and the scattering length, as=-84(+25)(-41) bohr, in good agreement with recent experimental measurements. The scattering length is predicted without any adjustment to experimental data for the first time for alkali-metal-atom collisions. We predict the permanent electric dipole moment in the rovibrational ground state, d0=0.167(1) debye. These values are obtained without any adjustment to experimental data, showing that quantum chemistry methods are capable of predicting scattering properties of many-electron systems, provided relatively weak interaction and small reduced mass of the system. |
Friday, June 4, 2021 9:12AM - 9:24AM Live |
X08.00007: Elastic and inelastic collisions of C60 in buffer gases probed by nonlinear spectroscopy Lee Liu, P. Bryan Changala, Jutta Toscano, Qizhong Liang, Marissa Weichman, Jun Ye C60, comprising 60 indistinguishable carbon atoms arranged on a spherical lattice, straddles the border between a molecule and extended material. Nonetheless, its rigid symmetrical structure makes it by far the largest molecule for which rotational quantum state resolution has been achieved [1]. |
Friday, June 4, 2021 9:24AM - 9:36AM Live |
X08.00008: Dynamical generation of spin squeezing in ultra-cold dipolar molecules Thomas Bilitewski, Luigi de Marco, Jun-Ru Li, Kyle Y Matsuda, William G Tobias, Giacomo Valtolina, Jun Ye, Ana Maria Rey We study the generation of spin-squeezing via long-range dipolar interactions in a quasi two-dimensional quantum degenerate dipolar molecular gas. To describe the many-body spin dynamics of the molecules we derive a long-range interacting XXZ model in the space of harmonic oscillator states and internal rotational levels valid in the regime where motional degrees of freedom are frozen. We predict the system to behave close to the collective limit resulting in robust spin dynamics and generation of entanglement in the form of spin squeezing even at finite temperature and in presence of dephasing and chemical reactions. We discuss how the internal state structure allows to realise time-reversal and robust metrological sensing protocols, enabling squeezing enhanced sensing of electric fields with dipolar molecular gases. |
Friday, June 4, 2021 9:36AM - 9:48AM Live |
X08.00009: AC stark shift of NH3 Induced by Strong Microwave Fields Manish Vashishta Manish Vashishta1, Katsunari Enomoto2, Pavle Djuricanin1, Takamasa Momose1 |
Friday, June 4, 2021 9:48AM - 10:00AM Live |
X08.00010: Quantum dynamics of a polar rotor acted upon by time-dependent electromagnetic pulses Mallikarjun Karra, Burkhard Schmidt, Bretislav Friedrich As a part of a larger objective to understand the quantum dynamics of a molecular rotor subject to few or single-cycle pulses with a bias, we present results for the simple case when the rotor is acted upon by a unipolar rectangular pulse. In our previous work [J. Chem. Phys. 149, 174109 (2018)], we demonstrated that a rotor interacting with finite-duration Gaussian pulses exhibits "resonances" in the coefficients of a rotational wavepacket initially prepared in its ground state and further leads to the diminishing of the kinetic energy ("rotational arrest") and orientation at particular values of the pulse duration. Herein, we reproduce the above results, both numerically and analytically, with the rectangular pulse and show, in addition, that the orientation becomes vanishingly small at pulse durations corresponding to the quasi-periodic "resonances" independent of the initial free-rotor state. Finally, we discuss experimental realizations and applications of the above control scheme to cold molecular rotors. |
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