Sequential phonon measurements of atomic motion

The motion of trapped atoms plays an essential role in quantum mechanical sensing, simulations and computing. Small disturbances of atomic vibrations are still challenging to be sensitively detected. It requires a reliable coupling between individual phonons and internal electronic levels that light can readout. As available information in a few electronic levels about the phonons is limited, the coupling needs to be sequentially repeated to further harvest the remaining information. We analyze such phonon measurements on the simplest example of the force and heating sensing using motional Fock states. We prove that two sequential measurements are sufficient to reach sensitivity to force and heating for realistic Fock states and saturate the quantum Fisher information for a small amount of force or heating. It is achieved by the conventionally available Jaynes-Cummings coupling. The achieved sensitivities are found to be better than those obtained from classical states. Further enhancements are expectable when the higher Fock state generation is improved. The result opens additional applications of sequential phonon measurements of atomic motion. This measurement scheme can also be directly applied to other bosonic systems including cavity QED and circuit QED.

On the transfer of theoretical multipole parameters for restoring static electron density and revealing and treating atomic anharmonic motion. Features of chemical bonding in crystals of an isocyanuric acid derivative

The crystal and electronic structure of an isocyanuric acid derivative was studied by high-resolution single-crystal X-ray diffraction within the Hansen–Coppens multipole formalism. The observed deformation electron density shows signs of thermal smearing. The experimental picture meaningfully assigned to the consequences of unmodelled anharmonic atomic motion. Straightforward simultaneous refinement of all parameters, including Gram–Charlier coefficients, resulted in more significant distortion of apparent static electron density, even though the residual density became significantly flatter and more featureless. Further, the method of transferring multipole parameters from the model refined against theoretical structure factors as an initial guess was employed, followed by the subsequent block refinement of Gram–Charlier coefficients and the other parameters. This procedure allowed us to appropriately distinguish static electron density from the contaminant smearing effects of insufficiently accounted atomic motion. In particular, some covalent bonds and the weak π...π interaction between isocyanurate moieties were studied via the mutual penetration of atomic-like kinetic and electrostatic potential φ-basins with complementary atomic ρ-basins. Further, local electronic temperature was applied as an advanced descriptor for both covalent bonds and noncovalent interactions. Total probability density function (PDF) of nuclear displacement showed virtually no negative regions close to and around the atomic nuclei. The distribution of anharmonic PDF to a certain extent matched the residual electron density from the multipole model before anharmonic refinement. No signs of disordering of the sulfonyl group hidden in the modelled anharmonic motion were found in the PDF.

Ultrafast dynamics and scattering of protic ionic liquids induced by XFEL pulses

X-rays are routinely used for structural studies through scattering, and femtosecond X-ray lasers can probe ultrafast dynamics. We aim to capture the femtosecond dynamics of liquid samples using simulations and deconstruct the interplay of ionization and atomic motion within the X-ray laser pulse. This deconstruction is resolution dependent, as ionization influences the low momentum transfers through changes in scattering form factors, while atomic motion has a greater effect at high momentum transfers through loss of coherence. Our methodology uses a combination of classical molecular dynamics and plasma simulation on a protic ionic liquid to quantify the contributions to the scattering signal and how these evolve with time during the X-ray laser pulse. Our method is relevant for studies of organic liquids, biomolecules in solution or any low-Z materials at liquid densities that quickly turn into a plasma while probed with X-rays.

Restless motion

Atoms in solids are in constant random motion. Their kinetic energy is heat. Heat associated with local regions may fluctuate. The size of the fluctuations increases with decreasing size of the region. Such fluctuations enable thermally activated processes to occur. At equilibrium interstitials and vacancies undergo random walks in solids, which gives rise to diffusion in crystals and reptation in polymers. The activation energy is the free energy barrier these defects have to overcome to jump between sites. Diffusion is biased by driving forces resulting from gradients of chemical potential. The mobility relates the drift velocity of defects to the driving force on them. The Einstein relation relates the mobility to the diffusivity. It is an example of the fluctuation-dissipation theorem. Atomic motion enables diffusion and limits mobility. Thermal expansion is also a consequence of atomic motion, resulting from a fundamental asymmetry in all interatomic forces.

Characterizations of Epicurean Atomism

This chapter relates the history of atomism from Democritus to Lucretius and provides a survey of major opponents of atomism from Aristotle to Cicero, the latter of whom provides valuable evidence for Hellenistic responses to atomism. Early Epicureans, including Epicurus himself, were suspicious of figurative language. In contrast, opponents of atomism, most notably Cicero, made frequent use of tendentious metaphors and analogies to associate atomic physics with the disorder of rioting crowds and failed states. It is likely that Virgil adopted his own negative attitude toward atomic imagery in the Aeneid, where atomic motion symbolizes political and cosmic disorder, from these earlier anti-atomist writers.

Quantum or Classical Perception of Atomic Motion

An assessment is given as to the extent to which pure unitary evolution, as distinct from environmental decohering interaction, can provide the transition necessary for an observer to perceive quantum dynamics as classical. This has implications for the interpretation of quantum wavefunctions as a characteristic of ensembles or of single particles and the related question of wavefunction “collapse”. A brief historical overview is presented as well as recent emphasis on the role of the semi-classical “imaging theorem” in describing quantum to classical unitary evolution.