Alexander D. Cronin

Optics and interferometry with atoms and molecules

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.

From Single- to Multiple-Photon Decoherence in an Atom Interferometer

We measure the decoherence of a spatially separated atomic superposition due to spontaneous photon scattering. We observe a qualitative change in decoherence versus separation as the number of scattered photons increases, and verify quantitatively the decoherence rate constant in the many-photon limit. Our results illustrate an evolution of decoherence consistent with general models developed for a broad class of decoherence phenomena.

An electron Talbot interferometer

We report the first demonstration of a Talbot interferometer for electrons. The interferometer was used to image the Talbot carpet behind a nano-fabricated material grating. The Talbot interferometer design uses two identical gratings, and is particularly sensitive to distortions of the incident wavefronts. To illustrate this we used our interferometer to measure the curvature of concave wavefronts in a weakly focused electron beam. We describe how this wavefront curvature demagnified the Talbot revivals, and we discuss further applications for electron Talbot interferometers.

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}{sub Na}=24.11(2){sub stat}(18){sub sys}x10{sup -24}cm{sup 3}, {alpha}{sub K}=43.06(14)(33), and {alpha}{sub 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% uncertainty. We find {alpha}{sub Rb}/{alpha}{sub Na}=1.959(5), {alpha}{sub K}/{alpha}{sub Na}=1.786(6), and {alpha}{sub Rb}/{alpha}{sub 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}{sub K}=43.06(21) and {alpha}{sub Rb}=47.24(21).

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 wavelike (coherent) behavior 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 Lifshitz theory for a nonretarded 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.

Electron diffraction from free-standing, metal-coated transmission gratings

Electron diffraction from a free-standing nanofabricated transmission grating was demonstrated, with energies ranging from 125 eV to 25 keV. Observation of 21 diffraction orders highlights the quality of the gratings. The image charge potential due to one electron was measured by rotating the grating. These gratings may pave the way to low-energy electron interferometry.

Comparing ramp rates from large and small PV systems, and selection of batteries for ramp rate control

We compare the AC power fluctuations from a 1.6 MW and a 2 kW photovoltaic (PV) system. Both of these PV generating stations exhibit fluctuations exceeding 50% of their rated capacity in under 10 seconds. The smaller system can fluctuate more rapidly, exhibiting 50% dropouts in 3 seconds. Although the MW-scale system covers 4000 times as much ground area, the bandwidth of the fluctuations is remarkably similar. We explore explanations for this observation, and we discuss the impact of this on battery sizing.

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.

Forecasts of PV power output using power measurements of 80 residential PV installs

We describe a new method to forecast the power output from photovoltaic (PV) systems under cloudy skies. We forecast cloud-induced fluctuations in output power by using measurements from 80 residential rooftop PV systems as an input to a forecasting algorithm described here. We compare the performance of our new method to results from our numerical weather model, and also to forecasts based on our images from a ground-based sun-tracking sky camera. Our numerical weather model provides forecasts of irradiance up to several days in advance. In comparison, our network of PV systems can forecast output up to an hour in advance. Our sky-camera image analysis algorithms can be used to forecast 10 minutes in advance. We also show how hybrid methods can improve the accuracy of hour-ahead forecasts.

Analysis of 80 rooftop PV systems in the Tucson, AZ area

We present field performance measurements of 80 rooftop systems in the Tucson, AZ region. We describe a framework that enables identification the causes of system performance variations. We can distinguish between shading, module orientation, outages, and weather conditions from the performance data alone, i.e., without physical inspection of the system. The modules used in the systems that we study are predominantly from 2 manufacturers: Sunpower and Schott, with two types of modules from each manufacturer. We show that the variation in system performance due to these four module types is smaller than the variations due to other system-level effects. We discuss the distribution of de-ratings due to shading, and de-ratings due to clouds, as well as the significance and duration of outages. We also examine the effect of system age on annual final yields.