Bulletin of the American Physical Society
2023 APS March Meeting
Volume 68, Number 3
Las Vegas, Nevada (March 510)
Virtual (March 2022); Time Zone: Pacific Time
Session Y65: Cold Molecules and Applications 
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Sponsoring Units: DAMOP Chair: JuanJose LietorSantos, American Physical Society Room: Room 414 
Friday, March 10, 2023 8:00AM  8:12AM 
Y65.00001: Multiband topological phases of periodically kicked molecules Volker Karle, Mikhail Lemeshko, Areg Ghazaryan We show that the simplest of existing molecules  closedshell diatomics not interacting with one another  host topologically nontrivial phases when driven by periodic faroffresonant laser pulses. A periodically kicked molecular rotor can be mapped onto a "crystalline" lattice in angular momentum space. This allows to define quasimomenta and the band structure in the Floquet representation, by analogy with the Bloch waves of solidstate physics. Applying laser pulses spaced by 1/3 of the molecular rotational period creates a lattice with three atoms per unit cell with staggered hopping, whose band structure features Dirac cones. These Dirac cones, topologically protected by reflection and timereversal symmetry, are reminiscent of (although not equivalent to) the ones seen in graphene. They  and the corresponding edge states  are broadly tunable by adjusting the laser intensities and can be observed in presentday experiments by measuring molecular alignment and populations of rotational levels. This paves the way to study controllable topological physics in gasphase experiments with small molecules as well as to classify dynamical molecular states by their topological invariants. 
Friday, March 10, 2023 8:12AM  8:24AM 
Y65.00002: Rovibrational spectroscopy of diatomic molecules using LaguerreGaussian beams Mikhail Maslov, Georgios Koutentakis, Mikhail Lemeshko We consider a diatomic molecule, like HCl or CS, interacting with the electric field of a LaguerreGaussian beam. We derive the Hamiltonian of the system within the harmonic approximation for the vibrational modes of the molecule. We study the angular momentum exchange between the vortex beam, rotation of the molecule and its centerofmass motion. We demonstrate analytically that the selection rules for the magnetic quantum number of the rotational state are determined by the orbital angular momentum of light. In particular, for LaguerreGaussian beams we predict novel transitions that are enabled by the nonzero vorticity of the electric field. These transitions can be resolved in stateoftheart spectroscopy experiments by comparing the absorption spectra produced by a plane wave and a vortex beam in the presence of a Stark field. Our findings are relevant for a broad range of molecular spectroscopy measurements and emphasize the prospective benefits of using vortex beams.

Friday, March 10, 2023 8:24AM  8:36AM 
Y65.00003: Resolution of Gauge Ambiguities in Molecular Cavity Quantum Electrodynamics Pengfei Huo We'll present our recent work on molecular cavity quantum electrodynamics by resolving the gauge ambiguities between the Coulomb gauge and the dipole gauge Hamiltonians under the electronic state truncation [1]. We conjecture that such ambiguity arises because not all operators are consistently constrained in the same truncated electronic subspace for both gauges. We resolve this ambiguity by constructing a unitary transformation operator that properly constrains all lightmatter interaction terms in the same subspace. We further derive an equivalent and yet convenient expression for the Coulomb gauge Hamiltonian under the truncated subspace. We finally provide the analytical and numerical results of a model molecular system coupled to the cavity to demonstrate the validity of our theory. 
Friday, March 10, 2023 8:36AM  8:48AM 
Y65.00004: Dispersion Interactions in a Molecular Crystal Jason Kattan, John E Sipe We implement a microsopic theory of polarization and magnetization, formulated within nonrelativistic quantum electrodynamics, to study radiative corrections to the electronic energy levels of a molecular crystal, arising from interactions between the chargecurrent distribution and quantum vacuum fluctuations of the electromagnetic field. To leading order in the fine structure constant, our renormalized level shift is valid for both electronic ground and excited states, and for an arbitrary number of lattice sites, including Nbody interactions for all positive integers N. In particular, our expression is a sum of onebody (onsite) terms, which are a direct generalization of Bethe's result for the Lamb shift in atomic Hydrogen, and additional terms corresponding to manybody intermolecular dispersion interactions between the lattice sites. Being formulated in terms of microscopic polarization and magnetization fields, we can expand our level shift in a sum of contributions coming from an arbitrary number of electric and magnetic multipole moments, so that individual multipole transitions can be isolated and studied. 
Friday, March 10, 2023 8:48AM  9:00AM 
Y65.00005: Cold collisions of aligned D_{2} molecules James Croft It has recently become experimentally possible to study inelastic collisions between two aligned D_{2} molecules at around 1 K. Such collisions between aligned molecules in the cold regime allow for the detailed interrogation and control of bimolecular collisions. Here, I discuss the theoretical formalism for collisions of aligned molecules, and apply the approach to stateprepared D_{2}. Based on fulldimensional quantum scattering calculations, on an accurate H_{2}H_{2} interaction potential, the experimental angular distributions are reproduced for different initial alignments. An analysis of the angular distribution reveals that the key features could primarily be attributed to a partial wave resonance with orbital angular momentum l=4. 
Friday, March 10, 2023 9:00AM  9:12AM 
Y65.00006: Nonadiabatic quantum effects in ultracold K + KRb → K_{2} + Rb chemical reaction Humberto da Silva, Hui Li, Brian K Kendrick, Svetlana Kotochigova, Balakrishnan Naduvalath More than a decade since the first measurement of the K + KRb(X^{1}Σ^{+},ν=0,N=0) ultracold chemical reaction at JILA [1], characterized by a rate constant of 1.7×10^{10} cm^{3}/s at about 250 nK, a theoretical study of this reaction remains a challenging endeavor. The only fulldimensional quantum reactive scattering simulation corresponds to that of Croft et al. [2]. The theoretical rate constant of Croft et al. underestimates the measurement value by about 35% but agrees with the value predicted by a universal model based purely on longrange forces. A possible source of the discrepancy is the neglect of the nonadiabatic coupling between the two lowest electronic states of the triatomic complex, coupled through a conical intersection at short ranges. In this work we account for the nonadiabatic effect in a diabatic representation of the coupled electronic states. We will discuss the methodology implemented in hyperspherical coordinates [3] and the possible role of quantum interference effects mediated by the conical intersection in bridging the gap between theory and experiment. 
Friday, March 10, 2023 9:12AM  9:24AM 
Y65.00007: Automated detection of laser cooling schemes for ultracold molecules Anna Dawid, Niccolò Bigagli, Daniel W Savin, Sebastian Will Ultracold molecules offer exciting prospects for quantum sciences, including quantum chemistry, sensing, and simulations. Their applications are, however, limited by the challenges in their cooling. So far, there were two main approaches to producing ultracold molecules: either by combining already ultracold atoms (resulting in, e.g., KRb and NaCs) or by laser cooling species with quasidiagonal FranckCondon factors (like SrF, CaF, and YO). Those ultracold species are far from being chemically typical, and thus their applications are limited outside fundamental physics. 
Friday, March 10, 2023 9:24AM  9:36AM 
Y65.00008: Vibrational Spectroscopy of a Single Polyatomic Molecule Scott Eierman Polyatomic molecular ions are of fundamental importance to fields ranging from biochemistry to atmospheric chemistry. Action spectroscopy methods which couple spectroscopy with mass spectrometry have enabled high resolution structural studies of otherwise inaccessible species, but all reported action techniques destroy the molecules being studied. We have developed a novel action technique in which cold molecular ions are cotrapped with lasercooled atomic ions and complexed with weakly bound, neutral "messenger" atoms/molecules. We remove these messengers by driving infrared vibrational transitions in the molecule, and we use cotrapped atomic ions as a nondestructive probe to monitor this process. By observing the frequency dependence of this messenger ejection rate we are able to directly determine the vibrational spectrum of the molecule while preserving it in our ion trap. Here we provide an overview of the instrument we have built for this new method, and present our first spectrum of a single tropylium cation. To our knowledge this is the first reported spectrum of a single gasphase polyatomic molecule. Our method is general to a broad class of molecules, and will open up new pathways for nondestructive, highresolution spectroscopy and structural analysis of molecular ions. 
Friday, March 10, 2023 9:36AM  9:48AM 
Y65.00009: Quantum Membrane Phases in Synthetic Lattices of Cold Molecules or Rydberg Atoms Chunhan Feng, Hannah Manetsch, Valery G Rousseau, Kaden Hazzard, Richard T Scalettar We calculate properties of dipolar interacting ultracold molecules or Rydberg atoms in a semisynthetic threedimensional configuration—one synthetic dimension plus a twodimensional realspace optical lattice or periodic microtrap array—using the stochastic Green's function quantum Monte Carlo method. Through a calculation of thermodynamic quantities and appropriate correlation functions, along with their finitesize scalings, we show that there is a secondorder transition to a lowtemperature phase in which twodimensional “sheets” form in the synthetic dimension of internal rotational or electronic states of the molecules or Rydberg atoms, respectively. Simulations for different values of the interaction V, which acts between atoms or molecules that are adjacent both in real and synthetic space, allow us to compute a phase diagram. We find a finitetemperature transition at sufficiently large V as well as a quantum phase transition—a critical value V_{c} below which the transition temperature vanishes. 
Friday, March 10, 2023 9:48AM  10:00AM 
Y65.00010: Error correction on molecular platforms Shubham Jain, Eric R Hudson, Wesley C Campbell, Victor V Albert Molecular rotational state spaces, modeled by infinite dimensional Hilbert spaces of quantum rigid rotors, present new grounds for robust quantum information processing. They are, however, prone to noise induced by the environment that surrounds them. As a step towards making qubits realizable through these rotorspace configurations, we study the effects of noise that are likely to be relevant while working with molecules immersed in a physical environment. One such noise model is a generalization of the brownian center of mass motion for quantum rigid bodies in a thermal environment^{[1]}. This kind of noise is found to be local in the angular position and angular momentum phase space of the rotor and hence, can be tamed with already existing molecular codes^{[2]}. Another relevant noise model is blackbody radiation affecting the molecules^{[}^{3,4]}. We highlight situations where this kind of noise can be highly nonlocal in the molecule’s phase space and characterize instances where conventional (i.e., exact) errorcorrection would fail. We comment on the different strategies that can circumvent this nogo result. 
Friday, March 10, 2023 10:00AM  10:12AM 
Y65.00011: Quantum sensing base on the conformational transitions of single molecules Wenlu Shi, Yunpeng Xia, Wilson Ho Advances in quantum sensors, including spin , charge , and flux qubits have demonstrated advantages in sensitivity and precision. Here, we realized a quantum sensing microscope based on transitions between different conformational states of a single adsorbed pyrrolidine in the STM junction. The conformational transitions can be induced by tunneling electrons or by light. The transition rate, population, and lifetime of the conformational states of a single pyrrolidine molecule attached to the apex of a STM tip showed subatomic scale variations over different lateral positions of a single layer of copper nitride (Cu_{2}N) surface. For a bare tip, these conformational transition statistics for an adsorbed pyrrolidine molecule showed a nearly isotropic spatial distribution on the Cu(001) surface, a twofold symmetric pattern on the Cu_{2}N surface, and sensitive coupling to an adjacent coadsorbed pyrrolidine molecule on Cu(001). Our results demonstrated the sensitivity of a twolevel system based on molecular conformation states for quantum sensing of soft and solid surfaces. The fact that the transitions were differently induced by electrons and light provided a pathway for controlling the states of the molecular qubits. 
Friday, March 10, 2023 10:12AM  10:24AM 
Y65.00012: Quantum Simulation of StronglyCorrelated Molecules with Rydberg Atom Arrays Nishad Maskara, James Shee, Stefan Ostermann, Abigail M Gomez, Rodrigo A Bravo, Derek Wang, Martin P HeadGordon, Susanne F Yelin, Mikhail D Lukin One of the promising applications for nearterm programmable quantum simulators is studying quantum chemistry and materials problems. In this project, we consider a hybrid quantumclassical research pipeline for studying lowenergy properties of certain molecules with strong spin correlations. The procedure starts with an effective model Hamiltonian, such as a Heisenberg model, governing the lowenergy spin behavior, computed with traditional quantum chemistry techniques. Then, a programmable quantum simulator can be used to probe the spectrum and eigenstates of the model. To efficiently simulate the dynamics, we develop a hardwareefficient encoding of higherspin Heisenberg models for Rydberg atom arrays, utilizing multiqubit gates, atom reconfiguration, and Floquet engineering. Then, we demonstrate how to extract both the spectrum and eigenstate properties of the model via snapshot measurements and ancillaassisted control, which accesses exponentially many twotime correlation functions. This information can be used to compute important chemical information, such as relative energy splittings between lowenergy spin states, and magnetic susceptibilities. Finally, we propose proofofconcept experiments studying organometallic catalysts and singlemolecular magnets for demonstrating these techniques. Our results provide a framework and roadmap for how quantum simulation can be used in collaboration with computational chemistry to study frontier problems in quantum chemistry and materials science. 
Friday, March 10, 2023 10:24AM  10:36AM 
Y65.00013: Examining molecular cluster dynamics of supercritical CO_{2} using ultrafast XPCS Arijit Majumdar Due to their wide range of applications, supercritical fluids (SCFs) have been a topic of active research. A unique property of SCFs is the formation of molecular clusters near the critical point, leading to a complex microstructure. These clusters have a significant influence on the thermophysical properties. The challenge in studying the dynamics of such cluster is their short length scale and lifetime. Split pulse xray photon correlation spectroscopy (XPCS), with its capability to capture molecular motion at picosecond time resolution, is an attractive choice to study the dynamics of these supercritical clusters. This work presents the first measurements of the cluster dynamics in SCFs using ultrafast XPCS. The experiments are performed on supercritical carbon dioxide. The measured intermediate scattering function, near the critical point, captures the density fluctuations due to cluster dynamics. A theoretical framework, coupled with molecular simulations, is developed to explain the experimental observations. 
Friday, March 10, 2023 10:36AM  10:48AM 
Y65.00014: Sumofproducts form of the molecular electronic Hamiltonian and its application within the MCTDH method Sudip Sasmal, Oriol Vendrell Romagosa A first principles quantum formalism to describe the nonadiabatic dynamics of electrons and nuclei based on a second quantization representation (SQR) of the electronic motion combined with the usual representation of the nuclear coordinates is introduced. This procedure circumvents the introduction of potential energy surfaces and nonadiabatic couplings, providing an alternative to the Born–Oppenheimer approximation. However, the major problem of this method applied to ab initio studies of large molecular systems remains the enormous size of the electronic SQR Hamiltonian, whose number of terms increases with the fourth power of the number of spinorbitals. We introduce three different approaches to represent the secondquantized electronic Hamiltonian in a sumofproducts form. These procedures aim at mitigating the quartic scaling of the number of terms in the Hamiltonian with respect to the number of spin orbitals, and thus enable applications to larger molecular systems. Here we describe the application of these approaches within the multiconfiguration timedependent Hartree framework. 
Friday, March 10, 2023 10:48AM  11:00AM 
Y65.00015: Atomicscale sensing by single molecule conformational transitions Dan Bai, Wenlu Shi, Wilson Ho Typical molecular transitions occur between two intrinsic states in a doublewell potential. Herein we show that a single molecule can exhibit multiple states in different environment of an atomicscale cavity. Taking advantage of the subangstrom resolution of the scanning tunneling microscope (STM), we report the strong spatial sensitivity of conformational transitions of a single pyrrolidine molecule adsorbed on Cu(001) terrace, Cu_{2}N monolayer islands, and onedimensional (1D) Cu row between Cu_{2}N islands. The molecule exhibits twolevel switching on Cu(001), threelevel on Cu_{2}N, and reversible transitions between twolevel and threelevel on 1D Cu row. Furthermore, the surface anisotropy of the Cu row leads to long timescale for the molecular switching between twolevel and threelevel transitions. The transition rate and the population and lifetime of the molecular levels exhibit high sensitivity on the local environment. These results extend our knowledge of molecule–substrate interaction and demonstrate the realization of multiplelevel states in a single molecule for processing quantum information and as molecular switches. 
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