30 research outputs found
Precise study of asymptotic physics with subradiant ultracold molecules
Weakly bound molecules have physical properties without atomic analogues,
even as the bond length approaches dissociation. In particular, the internal
symmetries of homonuclear diatomic molecules result in formation of two-body
superradiant and subradiant excited states. While superradiance has been
demonstrated in a variety of systems, subradiance is more elusive due to the
inherently weak interaction with the environment. Here we characterize the
properties of deeply subradiant molecular states with intrinsic quality factors
exceeding via precise optical spectroscopy with the longest
molecule-light coherent interaction times to date. We find that two competing
effects limit the lifetimes of the subradiant molecules, with different
asymptotic behaviors. The first is radiative decay via weak magnetic-dipole and
electric-quadrupole interactions. We prove that its rate increases
quadratically with the bond length, confirming quantum mechanical predictions.
The second is nonradiative decay through weak gyroscopic predissociation, with
a rate proportional to the vibrational mode spacing and sensitive to
short-range physics. This work bridges the gap between atomic and molecular
metrology based on lattice-clock techniques, yielding new understanding of
long-range interatomic interactions and placing ultracold molecules at the
forefront of precision measurements.Comment: 12 pages, 6 figure
Accurate determination of blackbody radiation shifts in a strontium molecular lattice clock
Molecular lattice clocks enable the search for new physics, such as fifth forces or temporal variations of fundamental constants, in a manner complementary to atomic clocks. Blackbody radiation (BBR) is a major contributor to the systematic error budget of conventional atomic clocks and is notoriously difficult to characterize and control. Here, we combine infrared Stark-shift spectroscopy in a molecular lattice clock and modern quantum chemistry methods to characterize the polarizabilities of the Sr2 molecule from dc to infrared. Using this description, we determine the static and dynamic blackbody radiation shifts for all possible vibrational clock transitions to the 10â16 level. This constitutes an important step toward millihertz-level molecular spectroscopy in Sr2 and provides a framework for evaluating BBR shifts in other homonuclear molecules
Precise Determination of Blackbody Radiation Shifts in a Strontium Molecular Lattice Clock
Molecular lattice clocks enable the search for new physics, such as fifth
forces or temporal variations of fundamental constants, in a manner
complementary to atomic clocks. Blackbody radiation (BBR) is a major
contributor to the systematic error budget of conventional atomic clocks and is
notoriously difficult to characterize and control. Here, we combine infrared
Stark-shift spectroscopy in a molecular lattice clock and modern quantum
chemistry methods to characterize the polarizabilities of the Sr molecule
from dc to infrared. Using this description, we determine the static and
dynamic blackbody radiation shifts for all possible vibrational clock
transitions to the level. This constitutes an important step towards
mHz-level molecular spectroscopy in Sr, and provides a framework for
evaluating BBR shifts in other homonuclear molecules.Comment: 6 pages, 4 figures, updated reference
Interaction between LiH molecule and Li atom from state-of-the-art electronic structure calculations
State-of-the-art ab initio techniques have been applied to compute the potential energy surface for the lithium atom interacting with the lithium hydride molecule in the BornâOppenheimer approximation. The interaction potential was obtained using a combination of the explicitly correlated unrestricted coupled-cluster method with single, double, and noniterative triple excitations [UCCSD(T)-F12] for the coreâcore and coreâvalence correlation and full configuration interaction for the valenceâvalence correlation. The potential energy surface has a global minimum 8743 cmâ1 deep if the LiâH bond length is held fixed at the monomer equilibrium distance or 8825 cmâ1 deep if it is allowed to vary. In order to evaluate the performance of the conventional CCSD(T) approach, calculations were carried out using correlation-consistent polarized valence X-tuple-zeta basis sets, with X ranging from 2 to 5, and a very large set of bond functions. Using simple two-point extrapolations based on the single-power laws Xâ2 and Xâ3 for the orbital basis sets, we were able to reproduce the CCSD(T)âF12 results for the characteristic points of the potential with an error of 0.49% at worst. The contribution beyond the CCSD(T)âF12 model, obtained from full configuration interaction calculations for the valenceâvalence correlation, was shown to be very small, and the error bars on the potential were estimated. At linear LiHâLi geometries, the ground-state potential shows an avoided crossing with an ion-pair potential. The energy difference between the ground-state and excited-state potentials at the avoided crossing is only 94 cmâ1. Using both adiabatic and diabatic pictures, we analyze the interaction between the two potential energy surfaces and its possible impact on the collisional dynamics. When the LiâH bond is allowed to vary, a seam of conical intersections appears at C2v geometries. At the linear LiHâLi geometry, the conical intersection is at a LiâH distance which is only slightly larger than the monomer equilibrium distance, but for nonlinear geometries it quickly shifts to LiâH distances that are well outside the classical turning points of the ground-state potential of LiH. This suggests that the conical intersection will have little impact on the dynamics of LiâLiH collisions at ultralow temperatures. Finally, the reaction channels for the exchange and insertion reactions are also analyzed and found to be unimportant for the dynamics
Phase protection of Fano-Feshbach resonances
Decay of bound states due to coupling with free particle states is a general phenomenon occurring at energy scales from MeV in nuclear physics to peV in ultracold atomic gases. Such a coupling gives rise to Fano-Feshbach resonances (FFR) that have become key to understanding and controlling interactionsâin ultracold atomic gases, but also between quasiparticles, such as microcavity polaritons. Their energy positions were shown to follow quantum chaotic statistics. In contrast, their lifetimes have so far escaped a similarly comprehensive understanding. Here, we show that bound states, despite being resonantly coupled to a scattering state, become protected from decay whenever the relative phase is a multiple of Ï. We observe this phenomenon by measuring lifetimes spanning four orders of magnitude for FFR of spinâorbit excited molecular ions with merged beam and electrostatic trap experiments. Our results provide a blueprint for identifying naturally long-lived states in a decaying quantum system
Femtosecond two-photon photoassociation of hot magnesium atoms: A quantum dynamical study using thermal random phase wavefunctions
Two-photon photoassociation of hot magnesium atoms by femtosecond laser
pulses, creating electronically excited magnesium dimer molecules, is studied
from first principles, combining \textit{ab initio} quantum chemistry and
molecular quantum dynamics. This theoretical framework allows for rationalizing
the generation of molecular rovibrational coherence from thermally hot atoms
[L. Rybak \textit{et al.}, Phys. Rev. Lett. {\bf 107}, 273001 (2011)]. Random
phase thermal wave functions are employed to model the thermal ensemble of hot
colliding atoms. Comparing two different choices of basis functions, random
phase wavefunctions built from eigenstates are found to have the fastest
convergence for the photoassociation yield. The interaction of the colliding
atoms with a femtosecond laser pulse is modeled non-perturbatively to account
for strong-field effects
Multi-sectoral impact assessment of an extreme African dust episode in the Eastern Mediterranean in March 2018
In late March 2018, a large part of the Eastern Mediterranean experienced an extraordinary episode of African dust, one of the most intense in recent years, here referred to as the âMinoan Redâ event. The episode mainly affected the Greek island of Crete, where the highest aerosol concentrations over the past 15 yeas were recorded, although impacts were also felt well beyond this core area. Our study fills a gap in dust research by assessing the multi-sectoral impacts of sand and dust storms and their socioeconomic implications. Specifically, we provide a multi-sectoral impact assessment of Crete during the occurrence of this exceptional African dust event. During the day of the occurrence of the maximum dust concentration in Crete, i.e. March 22nd, 2018, we identified impacts on meteorological conditions, agriculture, transport, energy, society (including closing of schools and cancellation of social events), and emergency response systems. As a result, the event led to a 3-fold increase in daily emergency responses compare to previous days associated with urban emergencies and wildfires, a 3.5-fold increase in hospital visits and admissions for Chronic Obstructive Pulmonary Disease (COPD) exacerbations and dyspnoea, a reduction of visibility causing aircraft traffic disruptions (eleven cancellations and seven delays), and a reduction of solar energy production. We estimate the cost of direct and indirect effects of the dust episode, considering the most affected socio-economic sectors (e.g. civil protection, aviation, health and solar energy production), to be between 3.4 and 3.8 million EUR for Crete. Since such desert dust transport episodes are natural, meteorology-driven and thus to a large extent unavoidable, we argue that the efficiency of actions to mitigate dust impacts depends on the accuracy of operational dust forecasting and the implementation of relevant early warning systems for social awareness.Thanks are due to FCT/MCTES for the financial support to CESAM (UIDP/50017/2020+UIDB/50017/2020) through national funds, and also to the Icelandic Research Fund for the grant no. 207057-051. Authors S.
Kazadzis and P. Kosmopoulos would like to acknowledge the European
Commission project EuroGEO e-shape (grant agreement No 820852). Also,
International Cooperative for Aerosol Prediction (ICAP) and NASA mission
researchers are gratefully for providing aerosol data for this study. Aurelio
Tobias was supported by MCIN/AEI/10.13039/501100011033 (grant
CEX2018-000794-S). S. Kutuzov acknowledges the Megagrant project
(agreement No. 075-15-2021-599, 8.06.2021)
Software for the frontiers of quantum chemistry:An overview of developments in the Q-Chem 5 package
This article summarizes technical advances contained in the fifth major release of the Q-Chem quantum chemistry program package, covering developments since 2015. A comprehensive library of exchangeâcorrelation functionals, along with a suite of correlated many-body methods, continues to be a hallmark of the Q-Chem software. The many-body methods include novel variants of both coupled-cluster and configuration-interaction approaches along with methods based on the algebraic diagrammatic construction and variational reduced density-matrix methods. Methods highlighted in Q-Chem 5 include a suite of tools for modeling core-level spectroscopy, methods for describing metastable resonances, methods for computing vibronic spectra, the nuclearâelectronic orbital method, and several different energy decomposition analysis techniques. High-performance capabilities including multithreaded parallelism and support for calculations on graphics processing units are described. Q-Chem boasts a community of well over 100 active academic developers, and the continuing evolution of the software is supported by an âopen teamwareâ model and an increasingly modular design