arXiv subjects

Alexander D. Cronin

Publications and source records attributed to Alexander D. Cronin.

At least 19 recordsLinked to original sources

arXiv2019

A Conditional Random Field Model for Context Aware Cloud Detection in Sky Images

A conditional random field (CRF) model for cloud detection in ground based sky images is presented. We show that very high cloud detection accuracy can be achieved by combining a discriminative classifier and a higher order clique potential in a CRF framework. The image is first divided into homogeneous regions using a mean shift clustering algorithm and then a CRF model is defined over these regions. The various parameters involved are estimated using training data and the inference is performed using Iterated Conditional Modes (ICM) algorithm. We demonstrate how taking spatial context into account can boost the accuracy. We present qualitative and quantitative results to prove the superior performance of this framework in comparison with other state of the art methods applied for cloud detection.

eess.IV↗

arXiv2016

Analysis of polarizability measurements made with atom interferometry

We present revised measurements of the static electric dipole polarizabilities of K, Rb, and Cs based on atom interferometer experiments presented in [Phys. Rev. A 2015, 92, 052513] but now re-analyzed with new calibrations for the magnitude and geometry of the applied electric field gradient. The resulting polarizability values did not change, but the uncertainties were significantly reduced. Then we interpret several measurements of alkali metal atomic polarizabilities in terms of atomic oscillator strengths $f_{ik}$, Einstein coefficients $A_{ik}$, state lifetimes $τ_{k}$, transition dipole matrix elements $D_{ik}$, line strengths $S_{ik}$, and van der Waals $C_6$ coefficients. Finally, we combine atom interferometer measurements of polarizabilities with independent measurements of lifetimes and $C_6$ values in order to quantify the residual contribution to polarizability due to all atomic transitions other than the principal $ns$-$np_J$ transitions for alkali metal atoms.

physics.atom-ph↗

arXiv2015

Measurements of the Ground-State Polarizabilities of Cs, Rb, and K using Atom Interferometry

We measured the ground-state static electric-dipole polarizabilities of Cs, Rb, and K atoms using a three-nanograting Mach-Zehnder atom beam interferometer. Our measurements provide benchmark tests for atomic structure calculations and thus test the underlying theory used to interpret atomic parity non-conservation experiments. We measured $α_{\mathrm{Cs}} = 4πε_0 \times 59.45(11) Å^3$, $α_{\mathrm{Rb}} = 4πε_0 \times 47.44(9) Å^3$, and $α_{\mathrm{K}} = 4πε_0 \times 42.97(8) Å^3$. In atomic units, these measurements are $α_{\mathrm{Cs}} = 401.2(7)$, $α_{\mathrm{Rb}} = 320.1(6)$, and $α_{\mathrm{K}} = 290.0(5)$. We report ratios of polarizabilities $α_{\mathrm{Cs}}/α_{\mathrm{Rb}} = 1.2532(10)$, $α_{\mathrm{Cs}}/α_{\mathrm{K}} = 1.3835(9)$, and $α_{\mathrm{Rb}}/α_{\mathrm{K}} = 1.1040(9)$ with smaller fractional uncertainty because the systematic errors for individual measurements are largely correlated. Since Cs atom beams have short de Broglie wavelengths, we developed measurement methods that do not require resolved atom diffraction. Specifically, we used phase choppers to measure atomic beam velocity distributions, and we used electric field gradients to give the atom interference pattern a phase shift that depends on atomic polarizability.

physics.atom-ph↗

arXiv2015

Atom Interferometer Gyroscope with Spin-Dependent Phase Shifts Induced by Light near a Tune-Out Wavelength

Tune-out wavelengths measured with an atom interferometer are sensitive to laboratory rotation rates because of the Sagnac effect, vector polarizability, and dispersion compensation. We observed shifts in measured tune-out wavelengths as large as 213 pm with a potassium atom beam interferometer, and we explore how these shifts can be used for an atom interferometer gyroscope.

physics.atom-ph↗

arXiv2013

Atom optical shop testing of electrostatic lenses using an atom interferometer

We used an atom interferometer for atom optical shop testing of lenses for atomic de Broglie waves. We measured focal lengths and spherical aberrations of electrostatic lenses in three independent ways based on contrast data, phase data, or calculations of de Broglie wavefront curvature. We report focal lengths of -2.5 km and -21.7 km with 5% uncertainty for different lenses. All three methods give consistent results. Understanding how lenses magnify and distort atom interference fringes helps improve atom beam velocity measurements made with phase choppers [New J. Phys. 13, 115007 (2011)], which in turn will improve the accuracy of atomic polarizability measurements.

physics.atom-ph↗

arXiv2012

Measurement of a magic-zero wavelength

Light at a magic-zero wavelength causes zero energy shift for an atom. We measured the longest magic-zero wavelength for ground state potassium atoms to be $λ_\textrm{zero}=768.971(1)$ nm, and we show how this provides an improved experimental benchmark for atomic structure calculations. This $λ_\textrm{zero}$ measurement determines the ratio of the potassium atom D1 and D2 line strengths with record precision. It also demonstrates a new application for atom interferometry, and we discuss how decoherence will fundamentally limit future measurements of magic-zero wavelengths.

physics.atom-ph↗

arXiv2010

Magic ratio of window width to grating period for Van der Waals potential measurements using material gratings

We report improved precision measurements of the Van der Waals potential strength ($C_3$) for Na atoms and a silicon-nitride (SiN$_x$) surface. We studied diffraction from nano-fabricated gratings with a particular "magic" open-fraction that allows us to determine $C_3$ without the need for separate measurements of the width of the grating openings. Therefore, finding the magic open-fraction improves the precision of $C_3$ measurements. The same effect is demonstrated for a grating with an arbitrary open-fraction by rotating it to a particular "magic" angle, yielding $C_3=3.42\pm 0.19 \textrm{eV} \mathring{\textrm{A}}^3$ for Na and a SiN$_x$ surface. This precision is sufficient to detect a change in $C_3$ due to a thin metal coating on the grating surface. We discuss the contribution to $C_3$ of core electrons and edge effects.

physics.atom-ph↗

arXiv2010

Absolute and ratio measurements of the polarizability of Na, K, and Rb with an atom interferometer

We measured the ground state electric dipole polarizability of sodium, potassium, and rubidium using a Mach-Zehnder atom interferometer with an electric field gradient. We find alpha_Na=24.11(2)_stat(18)_sys x 10^-24 cm^3, alpha_K=43.06(14)(33), and alpha_Rb=47.24(12)(42). Since these measurements were all performed in the same apparatus and subject to the same systematic errors we can present polarizability ratios with 0.3% precision. We find alpha_Rb/alpha_Na=1.959(5), alpha_K/alpha_Na=1.786(6), and alpha_Rb/alpha_K=1.097(5). We combine our ratio measurements with the higher precision measurement of sodium polarizability by Ekstrom et al. [Phys. Rev. A 51, 3883 (1995)] to find alpha_K=43.06(21) and alpha_Rb=47.24(21).

physics.atom-ph↗

arXiv2008

An electron Talbot interferometer

The Talbot effect, in which a wave imprinted with transverse periodicity reconstructs itself at regular intervals, is a diffraction phenomenon that occurs in many physical systems. Here we present the first observation of the Talbot effect for electron de Broglie waves behind a nanofabricated transmission grating. This was thought to be difficult because of Coulomb interactions between electrons and nanostructure gratings, yet we were able to map out the entire near-field interference pattern, the "Talbot carpet", behind a grating. We did this using a Talbot interferometer, in which Talbot interference fringes from one grating are moire'-filtered by a 2nd grating. This arrangement has served for optical, X-ray, and atom interferometry, but never before for electrons. Talbot interferometers are particularly sensitive to distortions of the incident wavefronts, and to illustrate this we used our Talbot interferometer to measure the wavefront curvature of a weakly focused electron beam. Here we report how this wavefront curvature demagnified the Talbot revivals, and we discuss applications for electron Talbot interferometers.

quant-ph↗

arXiv2007

Atom Interferometers

Interference with atomic and molecular matter waves is a rich branch of atomic physics and quantum optics. It started with atom diffraction from crystal surfaces and the separated oscillatory fields technique used in atomic clocks. Atom interferometry is now reaching maturity as a powerful art with many applications in modern science. In this review we first describe the basic tools for coherent atom optics including diffraction by nanostructures and laser light, three-grating interferometers, and double wells on AtomChips. Then we review scientific advances in a broad range of fields that have resulted from the application of atom interferometers. These are grouped in three categories: (1) fundamental quantum science, (2) precision metrology and (3) atomic and molecular physics. Although some experiments with Bose Einstein condensates are included, the focus of the review is on linear matter wave optics, i.e. phenomena where each single atom interferes with itself.

quant-ph↗

arXiv2007

Cover slip external cavity diode laser

The design of a 671 nm diode laser with a mode-hop-free tuning range of 40 GHz is described. This long tuning range is achieved by simultaneously ramping the external cavity length with the laser injection current. The external cavity consists of a microscope cover slip mounted on piezoelectric actuators. In such a configuration the laser output pointing remains fixed, independent of its frequency. Using a diode with an output power of 5-7 mW, the laser linewidth was found to be smaller than 30 MHz. This cover slip cavity and feedforward laser current control system is simple, economical, robust, and easy to use for spectroscopy, as we demonstrate with lithium vapor and lithium atom beam experiments.

physics.optics↗

arXiv2006

Electron interferometry with nano-gratings

We present an electron interferometer based on near-field diffraction from two nanostructure gratings. Lau fringes are observed with an imaging detector, and revivals in the fringe visibility occur as the separation between gratings is increased from 0 to 3 mm. This verifies that electron beams diffracted by nanostructures remain coherent after propagating farther than the Talbot length $z_T = 2d^2/λ$ = 1.2 mm, and hence is a proof of principle for the function of a Talbot-Lau interferometer for electrons. Distorted fringes due to a phase object demonstrates an application for this new type of electron interferometer.

physics.optics↗

arXiv2005

Matter-Wave Decoherence due to a Gas Environment in an Atom Interferometer

Decoherence due to scattering from background gas particles is observed for the first time in a Mach-Zehnder atom interferometer, and compared with decoherence due to scattering photons. A single theory is shown to describe decoherence due to scattering either atoms or photons. Predictions from this theory are tested by experiments with different species of background gas, and also by experiments with different collimation restrictions on an atom beam interferometer.

physics.atom-ph↗

arXiv2005

Measurement of atomic diffraction phases induced by material gratings

Atom-surface interactions can significantly modify the intensity and phase of atom de Broglie waves diffracted by a silicon nitride grating. This affects the operation of a material grating as a coherent beam splitter. The phase shift induced by diffraction is measured by comparing the relative phases of serveral interfering paths in a Mach-Zehnder Na atom interferometer formed by three material gratings. The values of the diffraction phases are consistent with a simple model which includes a van der Waals atom-surface interaction between the Na atoms and the silicon nitride grating bars.

physics.atom-ph↗

arXiv2005

Limitations of Nanotechnology for Atom Interferometry

Do van der Waals interactions determine the smallest nanostructures that can be used for atom optics? This question is studied with regard to the problem of designing an atom interferometer with optimum sensitivity to de Broglie wave phase shifts. The optimum sensitivity to acceleration and rotation rates is also considered. For these applications we predict that nanostructures with a period smaller than 40 nm will cause atom interferometers to perform poorly because van der Waals interactions adversely affect how nanostructure gratings work as beam-splitters.

physics.atom-ph↗

arXiv2005

de Broglie Wave Phase Shifts Induced by Surfaces Closer than 25 nm

Four atom optics experiments that each serve to measure atom-surface interactions near nanofabricated gratings are presented here. In these experiments atoms in a beam travel within 25 nm of a material grating bar, and the analysis incorporates phase shifts for the atomic de Broglie waves due to interactions betwen Na atoms and silicon nitride surfaces. One atom diffraction experiment determines the van der Waals coefficient $C_3=2.7\pm$0.8 meVnm$^3$, and one atom interferometer experiment determines $C_3=4\pm$1 meVnm$^3$. The results of all four experiments are consistent with the Lifshitz prediction that is explicitly calculated here for Na-silicon nitride to be $C_3=3.25$ meVnm$^3$. The four atom optics experiments and review of van der Waals theory are complemented by similar experiments using electron beams and analysis of image-charge effects.

physics.atom-ph↗

arXiv2005

Analysis of a Material Phase Shifting Element in an Atom Interferometer

The interaction of Na atoms with a surface was probed by inserting a nanofabricated material grating into one arm of an atom interferometer (IFM). This technique permits a direct measurement of the change in phase and coherence of matter waves as they pass within 25 nm of the grating bar surface. The practical concerns and challenges of making such a measurement are discussed here. Interference of spurious diffraction orders, IFM path overlap, and the partial obscuration of IFM beams are all important aspects of this experiment. The systematic effects that contribute to the measured phase shift and contrast are discussed.

physics.atom-ph↗

arXiv2005

Observation of atom wave phase shifts induced by van der Waals atom-surface interactions

The development of nanotechnology and atom optics relies on understanding how atoms behave and interact with their environment. Isolated atoms can exhibit wave-like (coherent) behaviour with a corresponding de Broglie wavelength and phase which can be affected by nearby surfaces. Here an atom interferometer is used to measure the phase shift of Na atom waves induced by the walls of a 50 nm wide cavity. To our knowledge this is the first direct measurement of the de Broglie wave phase shift caused by atom-surface interactions. The magnitude of the phase shift is in agreement with that predicted by quantum electrodynamics for a non-retarded van der Waals interaction. This experiment also demonstrates that atom-waves can retain their coherence even when atom-surface distances are as small as 10 nm.

physics.atom-ph↗