5,460 research outputs found
Ultralong-Range Rydberg Molecules in a Divalent-Atomic System
We report the creation of ultralong-range Sr molecules comprising one
ground-state atom and one atom in a Rydberg state
for ranging from 29 to 36. Molecules are created in a trapped ultracold
atomic gas using two-photon excitation near resonant with the
intermediate state, and their formation is detected through ground-state atom
loss from the trap. The observed molecular binding energies are fit with the
aid of first-order perturbation theory that utilizes a Fermi pseudopotential
with effective -wave and -wave scattering lengths to describe the
interaction between an excited Rydberg electron and a ground-state Sr atom.Comment: 5 pages, 2 figure
Probing Nonlocal Spatial Correlations in Quantum Gases with Ultra-long-range Rydberg Molecules
We present photo-excitation of ultra-long-range Rydberg molecules as a probe
of spatial correlations in quantum gases. Rydberg molecules can be created with
well-defined internuclear spacing, set by the radius of the outer lobe of the
Rydberg electron wavefunction . By varying the principal quantum number
of the target Rydberg state, the molecular excitation rate can be used to
map the pair-correlation function of the trapped gas . We
demonstrate this with ultracold Sr gases and probe pair-separation length
scales ranging from , which are on the order of the
thermal de Broglie wavelength for temperatures around 1 K. We observe
bunching for a single-component Bose gas of Sr and anti-bunching due to
Pauli exclusion at short distances for a polarized Fermi gas of Sr,
revealing the effects of quantum statistics.Comment: 6 pages, 5 figure
Creation of Rydberg Polarons in a Bose Gas
We report spectroscopic observation of Rydberg polarons in an atomic Bose
gas. Polarons are created by excitation of Rydberg atoms as impurities in a
strontium Bose-Einstein condensate. They are distinguished from previously
studied polarons by macroscopic occupation of bound molecular states that arise
from scattering of the weakly bound Rydberg electron from ground-state atoms.
The absence of a -wave resonance in the low-energy electron-atom scattering
in Sr introduces a universal behavior in the Rydberg spectral lineshape and in
scaling of the spectral width (narrowing) with the Rydberg principal quantum
number, . Spectral features are described with a functional determinant
approach (FDA) that solves an extended Fr\"{o}hlich Hamiltonian for a mobile
impurity in a Bose gas. Excited states of polyatomic Rydberg molecules
(trimers, tetrameters, and pentamers) are experimentally resolved and
accurately reproduced with FDA.Comment: 5 pages, 3 figure
Theory of excitation of Rydberg polarons in an atomic quantum gas
We present a quantum many-body description of the excitation spectrum of
Rydberg polarons in a Bose gas. The many-body Hamiltonian is solved with
functional determinant theory, and we extend this technique to describe Rydberg
polarons of finite mass. Mean-field and classical descriptions of the spectrum
are derived as approximations of the many-body theory. The various approaches
are applied to experimental observations of polarons created by excitation of
Rydberg atoms in a strontium Bose-Einstein condensate.Comment: 14 pages, 9 figures. arXiv admin note: substantial text overlap with
arXiv:1706.0371
The heats of formation of the haloacetylenes XCCY [X, Y = H, F, Cl]: basis set limit ab initio results and thermochemical analysis
The heats of formation of haloacetylenes are evaluated using the recent W1
and W2 ab initio computational thermochemistry methods. These calculations
involve CCSD and CCSD(T) coupled cluster methods, basis sets of up to spdfgh
quality, extrapolations to the one-particle basis set limit, and contributions
of inner-shell correlation, scalar relativistic effects, and (where relevant)
first-order spin-orbit coupling. The heats of formation determined using W2
theory are: \hof(HCCH) = 54.48 kcal/mol, \hof(HCCF) = 25.15 kcal/mol,
\hof(FCCF) = 1.38 kcal/mol, \hof(HCCCl) = 54.83 kcal/mol, \hof(ClCCCl) = 56.21
kcal/mol, and \hof(FCCCl) = 28.47 kcal/mol. Enthalpies of hydrogenation and
destabilization energies relative to acetylene were obtained at the W1 level of
theory. So doing we find the following destabilization order for acetylenes:
FCCF ClCCF HCCF ClCCCl HCCCl HCCH. By a combination of W1
theory and isodesmic reactions, we show that the generally accepted heat of
formation of 1,2-dichloroethane should be revised to -31.80.6 kcal/mol, in
excellent agreement with a very recent critically evaluated review. The
performance of compound thermochemistry schemes such as G2, G3, G3X and CBS-QB3
theories has been analyzed.Comment: Mol. Phys., in press (E. R. Davidson issue
Electron attachment to valence-excited CO
The possibility of electron attachment to the valence state of CO
is examined using an {\it ab initio} bound-state multireference configuration
interaction approach. The resulting resonance has symmetry;
the higher vibrational levels of this resonance state coincide with, or are
nearly coincident with, levels of the parent state. Collisional
relaxation to the lowest vibrational levels in hot plasma situations might
yield the possibility of a long-lived CO state.Comment: Revtex file + postscript file for one figur
Controlling the accuracy of the density matrix renormalization group method: The Dynamical Block State Selection approach
We have applied the momentum space version of the Density Matrix
Renormalization Group method (-DMRG) in quantum chemistry in order to study
the accuracy of the algorithm in the new context. We have shown numerically
that it is possible to determine the desired accuracy of the method in advance
of the calculations by dynamically controlling the truncation error and the
number of block states using a novel protocol which we dubbed Dynamical Block
State Selection (DBSS). The relationship between the real error and truncation
error has been studied as a function of the number of orbitals and the fraction
of filled orbitals. We have calculated the ground state of the molecules
CH, HO, and F as well as the first excited state of CH. Our
largest calculations were carried out with 57 orbitals, the largest number of
block states was 1500--2000, and the largest dimensions of the Hilbert space of
the superblock configuration was 800.000--1.200.000.Comment: 12 page
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