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ATOM OPTICS, CORE ELECTRONS, AND THE VAN DER WAALS POTENTIAL

Vincent Lonij

Published Jan 1, 2011• 1 citation
OpenAlex

Abstract

This dissertation describes new measurements of the van der Waals (vdW) potential energy for atoms near a surface. The measurements presented here were accomplished by studying diffraction a beam of atoms transmitted through a nanograting. I will describe how we improved precision by a factor of 10 over previous diffraction measurements by studying how different types of atoms interact with the same surface. As a result of this new precision, we were able to show for the first time the contribution of atomic core electrons to the atom-surface potential, and experimentally test different atomic structure calculation methods.In addition, this dissertation will describe how changing the width of the grating bars to achieve a particular "magic" grating bar width or rotating a grating to a particular "magic" angle allows us to determine both the atom-surface potential strength and the geometry of the grating. This represents an improvement over several recent studies where uncertainties in the nanograting geometry limited precision in the measurements of the vdW potential.For a complementary measurement, also discussed in this dissertation, we collaborated with the Vigue group in Toulouse, France. In this collaboration we used an atom interferometer to measure the phase shift due to transmission through a nanograting. By combining diffraction data from Tucson with interferometry data from Toulouse we improved the precision of interferometry measurements of the atom-surface potential of a single atomic species by almost a factor of 10 over previous interferometric measurements of the vdW potential. These interferometry measurements also serve to measure the shape of the vdW potential and set a limit on non-Newtonian gravitational interactions at 1-2 nm length scales.Finally, this dissertation will discuss how nanogratings with optimized geometry can improve atom interferometers, for example, with blazed gratings. We discuss next generation atom-surface potential measurements and examine new ways of analyzing diffraction data.

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Dispersive atom interferometry phase shifts due to atom-surface interactions

S. Lepoutre, Haikel Jelassi, Vincent Lonij +4 more

We used the Toulouse atom interferometer to study how Van der Waals (VdW) interactions between atoms and surfaces cause velocity-dependent phase shifts for atomic de Broglie waves. By introducing a thin nano-grating in one branch of this interferometer, we observed a phase shift that depends on velocity to the power −0.49. This dispersion serves to measure both the strength and the position dependence of the atom-surface potential in the range from 5 to 10 nm from the surface, and it can also set new limits on non-Newtonian gravity in the 2 nm range.

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Atom Diffraction Reveals the Impact of Atomic Core Electrons on Atom-Surface Potentials

Vincent Lonij, Catherine E. Klauss, William F. Holmgren +1 more

We measured ratios of van der Waals potential coefficients (C3) for different atoms (Li, Na, K, and Rb) interacting with the same surface by studying atom diffraction from a nanograting. These measurements are a sensitive test of atomic structure calculations because C3 ratios are strongly influenced by core electrons and only weakly influenced by the permittivity and geometry of the surface. Our measurement uncertainty of 2% in the ratio C(3)(K)/C(3)(Na) is close to the uncertainty of the best theoretical predictions, and some of these predictions are inconsistent with our measurement.

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Using atomic diffraction of Na from material gratings to measure atom-surface interactions

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In atom optics a material structure is commonly regarded as an amplitude mask for atom waves. However, atomic diffraction patterns formed using material gratings indicate that material structures also operate as phase masks. In this study a well collimated beam of sodium atoms is used to illuminate a silicon nitride grating with a period of 100 nm. During passage through the grating slots atoms acquire a phase shift due to the van der Waals (vdW) interaction with the grating walls. As a result the relative intensities of the matter-wave diffraction peaks deviate from those expected for a purely absorbing grating. Thus a complex transmission function is required to explain the observed diffraction envelopes. An optics perspective to the theory of atomic diffraction from material gratings is put forth in the hopes of providing a more intuitive picture concerning the influence of the vdW potential. The van der Waals coefficient ${C}_{3}=2.7\ifmmode\pm\else\textpm\fi{}0.8\phantom{\rule{0.3em}{0ex}}\mathrm{meV}\phantom{\rule{0.3em}{0ex}}{\mathrm{nm}}^{3}$ is determined by fitting a modified Fresnel optical theory to the experimental data. This value of ${C}_{3}$ is consistent with a van der Waals interaction between atomic sodium and a silicon nitride surface.

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Using Atomic Diffraction of Na from Material Gratings to Measure Atom-Surface Interactions

John D. Perreault, Alexander D. Cronin, Tim A. Savas

In atom optics a material structure is commonly regarded as an amplitude mask for atom waves. However, atomic diffraction patterns formed using material gratings indicate that material structures also operate as phase masks. In this study a well collimated beam of sodium atoms is used to illuminate a silicon nitride grating with a period of 100 nm. During passage through the grating slots atoms acquire a phase shift due to the van der Waals interaction with the grating walls. As a result the relative intensities of the matter-wave diffraction peaks deviate from those expected for a purely absorbing grating. Thus a complex transmission function is required to explain the observed diffraction envelopes. An optics perspective to the theory of atomic diffraction from material gratings is put forth in the hopes of providing a more intuitive picture concerning the influence of the vdW potential. The van der Waals coefficient $C_{3} = 2.7\pm 0.8{meV nm}^{3}$ is determined by fitting a modified Fresnel optical theory to the experimental data. This value of $C_{3}$ is consistent with a van der Waals interaction between atomic sodium and a silicon nitride surface.

arXiv:physics/0312123•Dec 19, 2003•0 citations

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

Vincent Lonij, William F. Holmgren, Alexander D. Cronin

We report improved precision measurements of the van der Waals potential strength $({C}_{3})$ for Na atoms and a silicon-nitride $({\text{SiN}}_{x})$ surface. We studied diffraction from nanofabricated 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 ${C}_{3}=3.42\ifmmode\pm\else\textpm\fi{}0.19\text{ }\text{eV}\text{ }{\text{\AA{}}}^{3}$ for Na and a ${\text{SiN}}_{x}$ 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.

arXiv:0904.3289•Physical Review A•Dec 18, 2009•24 citations

Using atom optics to measure van der Waals atom-surface interactions

John D. Perreault

Atom-surface interactions are becoming an integral part of the field of atom optics. Here the role of van der Waals atom-surface interactions in atom wave diffraction and interferometry are investigated. In particular, it is shown that van der Waals interactions influence the intensity and phase of atomic diffraction patterns obtained from material gratings. As a result the atomic diffraction patterns are utilized to make an accurate determination of the interaction strength and verify the spatial variation of the atom-surface potential. A theory for describing the modified atom wave diffraction patterns is developed through an analogy with optical waves. An atom interferometer is used to directly measure the de Broglie wave phase shift induced by atom-surface interactions. More specifically, the phases of the zeroth, first, and second diffraction orders are measured. A proposal for using electromagnetic fields to modify the van der Waals interaction is put forth. Several of the important experimental components for observing such an effect are also demonstrated.

•Jan 1, 2005•0 citations
This dissertation describes new measurements of the van der Waals (vdW) potential energy for atoms near a surface. The measurements presented here were accomplished by studying diffraction a beam of atoms transmitted through a nanograting. I will describe how we improved precision by a factor of 10 over previous diffraction measurements by studying how different types of atoms interact with the same surface. As a result of this new precision, we were able to show for the first time the contribution of atomic core electrons to the atom-surface potential, and experimentally test different atomic structure calculation methods.In addition, this dissertation will describe how changing the width of the grating bars to achieve a particular "magic" grating bar width or rotating a grating to a particular "magic" angle allows us to determine both the atom-surface potential strength and the geometry of the grating. This represents an improvement over several recent studies where uncertainties in the nanograting geometry limited precision in the measurements of the vdW potential.For a complementary measurement, also discussed in this dissertation, we collaborated with the Vigue group in Toulouse, France. In this collaboration we used an atom interferometer to measure the phase shift due to transmission through a nanograting. By combining diffraction data from Tucson with interferometry data from Toulouse we improved the precision of interferometry measurements of the atom-surface potential of a single atomic species by almost a factor of 10 over previous interferometric measurements of the vdW potential. These interferometry measurements also serve to measure the shape of the vdW potential and set a limit on non-Newtonian gravitational interactions at 1-2 nm length scales.Finally, this dissertation will discuss how nanogratings with optimized geometry can improve atom interferometers, for example, with blazed gratings. We discuss next generation atom-surface potential measurements and examine new ways of analyzing diffraction data.
We used the Toulouse atom interferometer to study how Van der Waals (VdW) interactions between atoms and surfaces cause velocity-dependent phase shifts for atomic de Broglie waves. By introducing a thin nano-grating in one branch of this interferometer, we observed a phase shift that depends on velocity to the power −0.49. This dispersion serves to measure both the strength and the position dependence of the atom-surface potential in the range from 5 to 10 nm from the surface, and it can also set new limits on non-Newtonian gravity in the 2 nm range.
We measured ratios of van der Waals potential coefficients (C3) for different atoms (Li, Na, K, and Rb) interacting with the same surface by studying atom diffraction from a nanograting. These measurements are a sensitive test of atomic structure calculations because C3 ratios are strongly influenced by core electrons and only weakly influenced by the permittivity and geometry of the surface. Our measurement uncertainty of 2% in the ratio C(3)(K)/C(3)(Na) is close to the uncertainty of the best theoretical predictions, and some of these predictions are inconsistent with our measurement.
In atom optics a material structure is commonly regarded as an amplitude mask for atom waves. However, atomic diffraction patterns formed using material gratings indicate that material structures also operate as phase masks. In this study a well collimated beam of sodium atoms is used to illuminate a silicon nitride grating with a period of 100 nm. During passage through the grating slots atoms acquire a phase shift due to the van der Waals (vdW) interaction with the grating walls. As a result the relative intensities of the matter-wave diffraction peaks deviate from those expected for a purely absorbing grating. Thus a complex transmission function is required to explain the observed diffraction envelopes. An optics perspective to the theory of atomic diffraction from material gratings is put forth in the hopes of providing a more intuitive picture concerning the influence of the vdW potential. The van der Waals coefficient ${C}_{3}=2.7\ifmmode\pm\else\textpm\fi{}0.8\phantom{\rule{0.3em}{0ex}}\mathrm{meV}\phantom{\rule{0.3em}{0ex}}{\mathrm{nm}}^{3}$ is determined by fitting a modified Fresnel optical theory to the experimental data. This value of C3{C}_{3}C3​ is consistent with a van der Waals interaction between atomic sodium and a silicon nitride surface.
In atom optics a material structure is commonly regarded as an amplitude mask for atom waves. However, atomic diffraction patterns formed using material gratings indicate that material structures also operate as phase masks. In this study a well collimated beam of sodium atoms is used to illuminate a silicon nitride grating with a period of 100 nm. During passage through the grating slots atoms acquire a phase shift due to the van der Waals interaction with the grating walls. As a result the relative intensities of the matter-wave diffraction peaks deviate from those expected for a purely absorbing grating. Thus a complex transmission function is required to explain the observed diffraction envelopes. An optics perspective to the theory of atomic diffraction from material gratings is put forth in the hopes of providing a more intuitive picture concerning the influence of the vdW potential. The van der Waals coefficient C3=2.7±0.8meVnm3C_{3} = 2.7\pm 0.8{meV nm}^{3}C3​=2.7±0.8meVnm3 is determined by fitting a modified Fresnel optical theory to the experimental data. This value of C3C_{3}C3​ is consistent with a van der Waals interaction between atomic sodium and a silicon nitride surface.
We report improved precision measurements of the van der Waals potential strength (C3)({C}_{3})(C3​) for Na atoms and a silicon-nitride (SiNx)({\text{SiN}}_{x})(SiNx​) surface. We studied diffraction from nanofabricated gratings with a particular ``magic'' open fraction that allows us to determine C3{C}_{3}C3​ without the need for separate measurements of the width of the grating openings. Therefore, finding the magic open fraction improves the precision of C3{C}_{3}C3​ measurements. The same effect is demonstrated for a grating with an arbitrary open fraction by rotating it to a particular ``magic'' angle, yielding ${C}_{3}=3.42\ifmmode\pm\else\textpm\fi{}0.19\text{ }\text{eV}\text{ }{\text{\AA{}}}^{3}$ for Na and a SiNx{\text{SiN}}_{x}SiNx​ surface. This precision is sufficient to detect a change in C3{C}_{3}C3​ due to a thin metal coating on the grating surface. We discuss the contribution to C3{C}_{3}C3​ of core electrons and edge effects.
Atom-surface interactions are becoming an integral part of the field of atom optics. Here the role of van der Waals atom-surface interactions in atom wave diffraction and interferometry are investigated. In particular, it is shown that van der Waals interactions influence the intensity and phase of atomic diffraction patterns obtained from material gratings. As a result the atomic diffraction patterns are utilized to make an accurate determination of the interaction strength and verify the spatial variation of the atom-surface potential. A theory for describing the modified atom wave diffraction patterns is developed through an analogy with optical waves. An atom interferometer is used to directly measure the de Broglie wave phase shift induced by atom-surface interactions. More specifically, the phases of the zeroth, first, and second diffraction orders are measured. A proposal for using electromagnetic fields to modify the van der Waals interaction is put forth. Several of the important experimental components for observing such an effect are also demonstrated.