David Weiss - US grants

Long and Medium-Term Research: Quantum Nondemolition Measurements in Microwave Cavities This award is under the Long and Medium-Term Research at Foreign Centers of Excellence Program, which enables U.S. scientists and engineers to conduct three to twelve months of research abroad at research centers of proven excellence. The program's awards provide opportunities for joint research, and the use of unique or complementary facilities, expertise and experimental conditions abroad. This award will support a twelve-month postdoctoral research visit by Dr. David Weiss of Stanford University to work with Professor Serge Haroche at L'Ecole Normale Superieure. This project is in the field of Quantum Optics, specifically in Cavity Quantum Electrodynamics. An apparatus is currently under construction at L'Ecole Normale Superieure which will enable the field in a high finesse microwave cavity to be measured using beams of atoms in a long-lived Rydberg states. The cavity is detuned from an atomic resonance so that while the atoms experience a measurable energy shift due to light in the cavity, they do not absorb any of the cavity's photons. This so-called quantum non-demolition scheme is the first that promises to allow measurements of extremely weak fields, down to the single photon level. The likely first experiments using this system will be the preparation of non-classical states of the field, including pure number states, where the exact number of photons is determined at the expense of all knowledge of the field's phase, and "Schrodinger cat" states, which are coherent superpositions of different classical fields. The award recommendation provides funds to cover international travel and a stipend for twelve months.

9351541 Weiss This project involves fundamental changes in the ways statistics is taught in required and advanced undergraduate statistics courses in psychology. Students, many of whom have poor academic preparation and/or language difficulties, benefit from a highly visual and interactive learning environment by using an electronic classroom facility that contains student workstations with computers linked an instructor's station, as well as to the department and university computer networks. Mathematical and statistical illustrations are presented in a manner which enhances concepts. Students also perform appropriate exercises while the instructor monitors their progress and interacts with them. It is expected that the facility will also benefit instruction in experimental psychology, testing, and courses in computer applications in psychology. ***

It is proposed to construct a far-detuned 3-dimensional optical lattice that can act as an atomic trap. Cooling of the atoms in the trap will be achieved by successive vibrational excitation and de-excitation in the vibrational wells set up by the optical waves. Once the atoms have been appropriately cooled, they will be used for precision measurements of atomic properties. In addition, vibrational cooling of two atoms at a single lattice site will be used as the starting point for the creation of cold, trapped molecules.

This experimental research program is aimed at a series of experiments with interacting cold atoms in far-off-resonant optical lattices. The group will create and study one-dimensional and two-dimensional systems of bosons with widely varying coupling strengths and an unprecedented level of control. The first system to be studied is one-dimensional Bose gases, particularly in the strong coupling limit. The strongly interacting bosons "fermionize", i.e., their probability distribution is identical to that of non-interacting fermions in one dimension. The next proposed measurement is of g(2), the second order correlation function of the one-dimensional Bose gas, using a photoassociation technique. In the strong coupling limit, g(2) is expected to approach zero because of fermion-like repulsion. The group will also measure one-dimensional boson momentum distributions. These are sensitive to wavefunction amplitudes, not probabilities, so the momentum distributions differ in a characteristic way for fermionized one-dimensional bosons and real fermions. The broader impact of the program involves student education as well as applications to quantum mechanical devices.

Goals of the project: (1) To recruit and select bright students, including women, individuals with diverse backgrounds with respect to geographical origin and ethnicity, and students from non-Ph.D.-granting institutions where research possibilities are limited. (2) To involve students in basic, experimental research in microbiology. (3) To expose students to a broad range of bioscience research. (4) To develop each student's critical-thinking skills. (5) To develop each student's ability to record, analyze, and present scientific information. Overall, the goal is to promote the students' interests in scientific careers and to enhance their likelihood for success.
Means of achieving the goals: The student participants will be integrated into faculty research programs and will be expected to perform like beginning graduate students. Informal faculty-student discussions plus weekly seminars will supplement the laboratory research. Weekly informal lunches, two picnics and a banquet will facilitate social and scientific interactions. At the end of each summer's program, the students will prepare oral presentations to be given at a Summer Program Symposium. Each student will also prepare a written research report, under the guidance of the student's mentor.
Overall significance: Summer research programs are very valuable settings for bright students to experience basic scientific research. A significant fraction of the summer students do not have research opportunities at their institutions and might choose non-science careers due to lack of exposure to basic research. Of course not all students who participate in summer research programs in basic science choose careers in basic science, but experience shows that nearly all of the students to go on to post-graduate training in a graduate or professional school. The graduates of summer programs who do choose to go on to graduate school in science have a much better idea of what to expect, and they have a much greater chance of success.

Passamaquoddy has been spoken continuously in Eastern Maine for 9,000 years. It is the last surviving language of first contact in New England, yet it could be extinct within twenty-five years. A National Science Foundation grant will support an innovative project that will add a new dimension to language documentation and preservation by using filmmaking to reconnect the fractured bond between language, place, and community.

Documentary filmmaker Ben Levine will film groups in sacred places to stimulate deep memory and extended group discourse, and bring the language back into the public forum. The goal is to reverse the loss of public discourse symptomatic of language extinction. Linguist Robert Leavitt will use the filming to analyze historical, ecological, and linguistic information important to Passamaquoddy worldview and identity for a dictionary that has become an important resource for a new generation. Northeast Historic Film will use digital technology to help avoid obsolescence of the archival material.

The project offers historians, linguists, ecologists, sustainability designers and others access to cultural materials from a people whose survival skills shaped the American experience. The film may also show a new way to language survival for others.

This experimental research program is a new project to search for a non-zero electron electric dipole moment (eEDM) using ultracold cesium and rubidium atoms in one-dimensional optical (1D) lattice traps. Atoms will be loaded into a pair of parallel 1D far-off-resonant optical lattice traps in a magnetically shielded region of space. Their EDMs will be measured by observing their coherent evolution in electric fields that are directed oppositely in the two traps. The projected sensitivity is three parts in ten to the 30th, a 500-fold improvement over the current limit. Systematic errors can be kept at or below this statistical sensitivity. A particle with a permanent edm implies that both time-reversal (T) invariance and parity (P) invariance are violated. Both of these symmetries are violated in the standard model of physics, but at very small levels. Observation of a non-zero eEDM at the sensitivity of this experiment would provide definitive evidence for phenomena beyond the Standard Model of particle physics. Currently favored theories involving supersymmetry typically predict an electron EDM within a few orders of magnitude of the current limit. Continued non-observation of eEDMs would place stringent limits on extensions to the Standard Model. The broader impact of the program is student training of undergraduates, graduate students, and postdoctoral fellows.

Abstract
This project, "The Language Keepers" (NSF grant BCS-05533791, 2006-2008), addresses a central dilemma in documenting endangered languages: the decline and loss of public group discourse. The documenting of public group discourse provides linguists and Native-language teachers and students with a necessary research and learning resource. The work continues a successful Native-language documentation methodology in the Passamaquoddy communities of Maine, demonstrating the feasibility of stimulating renewed group conversation and filming natural, spontaneously spoken Passamaquoddy, especially in time-critical and culturally significant areas.

There are two components: First, the project uses the video documentation itself as feedback to participants to stimulate reflection and further discourse, creating a revived community dialogue in Passamaquoddy. Next, the existing conversational video corpus of transcribed, translated and subtitled "whole conversations," plus new conversations to be filmed, will be re-conceptualized as a non-linear, web-accessed, video database archive. This video database will be linked to the existing on-line dictionary data base. Viewers will then be able to create clusters of video and dictionary entries that contextualize the meaning of an item, conveying deeper cultural and linguistic understanding. This resource, which can be found online at www.languagekeepers.org, makes the linguistic complexity of Passamaquoddy more accessible and enables the development of innovative materials for teacher training, language learning, and research.

This REU Site award to The University of Iowa, located in Iowa City, IA, will support the training of 8 students for 10 weeks during the summers of 2016-2018. The scientific focus of the research program is microbiology. Each student will conduct an independent laboratory research project under the guidance of a faculty and a graduate student co-mentor from the Department of Microbiology. Lectures, workshops and cohort-building activities will promote professional development, familiarize students with graduate school and career options, and provide training in responsible conduct of research. Students will present their findings at a University-wide symposium and at regional and national meetings. The program is open to undergraduates who are interested in scientific research and are U.S. citizens or permanent residents. Recruitment will use both traditional mailings and various forms of electronic outreach. Special emphasis will be given to recruitment of students from demographic groups that are underrepresented in the sciences and/or students from small colleges (including community colleges) where opportunities for research are lacking. Students will be selected based on academic record, letters of recommendation and potential for outstanding research in the biological sciences. Post-program mentoring will promote retention of students in the sciences, while tracking will assess the lasting influences of the research experience.

It is anticipated that a total of 24 students, primarily from schools with limited research opportunities, will be trained in the program. Students will learn how research is conducted, and many will present the results of their work at scientific conferences.

A common web-based assessment tool used by all REU programs funded by the Division of Biological Infrastructure (Directorate for Biological Sciences) will be used to determine the effectiveness of the training program. Students will be tracked after the program in order to determine student career paths. Students will be asked to respond to an automatic email sent via the NSF reporting system. More information about the program is available by visiting http://www.medicine.uiowa.edu/microbiology/summer/, or by contacting the PI (Dr. David Weiss at david-weiss@uiowa.edu) or the co-PI (Dr. Linda McCarter at linda-mccarter@uiowa.edu).

This project involves a series of experiments with interacting cold atoms in far-off-resonance optical lattices. Arrays of coupled and independent one-dimensional (1D) gases of bosons will be prepared and studied to help resolve some outstanding mysteries of quantum statistical mechanics and quantum phase transitions. Prior experiments by the group have explored the physics of Bose-gases in one dimension, demonstrating that these gases never thermalize. In order to explore the crossover between one-dimensional and three-dimensional behavior, new experiments will relax the conditions that make 1D atomic gases not thermalize, and will apply new tools to measuring the onset of thermalization. In particular, a low energy 1D atom collider will be developed. These experiments will address a long open theoretical question of the existence of a threshold for chaos in a many-body quantum system, as there is in classical mechanics. This project may clarify how irreversibility of macroscopic behavior arises from the reversible behavior of individual atoms. In addition, 1D gas momentum distributions will be measured for the first time, and two-dimensional (2D) gases with variable interactions will be studied.

The broader impact of this work lies in the ability of cold-atom experiments to provide answers to long-open questions in nonlinear dynamics and mathematical physics. These experiments will train undergraduate, graduate, and postdoctoral researchers in this technologically-important area of physics.

The existence of an elementary particle with a permanent electric dipole moment (EDM) would imply that the basic equations of physics are different when time is reversed or all spatial coordinates (parity) are inverted. Although these symmetries are an integral part of classical physics, both are known to be violated in the current "Standard Model" of particle physics. In fact, there have been many direct observations of parity violation, and several indirect measurements of time reversal symmetry breaking. EDMs, however, have yet to be observed. The major motivation for trying to observe EDMs is that most proposed extensions to the Standard Model (such as supersymmetry) predict EDMs that are in the vicinity of the current experimental upper limit, whereas the Standard Model predicts that they should be much smaller. Increasing the precision of experiments could rule out possible extensions to the Standard Model, or provide the first experimental result that cannot be incorporated into the Standard Model. As such it would be a harbinger of a theoretical revolution. To measure the electron EDM, cesium atoms will be cooled with laser beams and trapped with light, and then their internal energy states will be measured in a very large electric field in a very low magnetic field environment. Undergraduates and graduate students will be trained in the use of these tools, which have many applications beyond this measurement.

The electron EDM will be searched for in this experiment using laser-cooled cesium atoms. The apparatus construction part of the experiment will be completed and data collection will commence. In the experiment, atoms are loaded into a pair of parallel one-dimensional far-off-resonant optical lattice traps in a magnetically shielded region of space, laser-cooled and optically pumped. Similar to the way permanent magnetic dipole measurements are routinely measured by looking for linear Zeeman energy shifts in magnetic fields, the EDM will be searched for by looking for linear Stark shifts in an electric field. The experiment is designed to be insensitive to magnetic fields and magnetic field gradients by simultaneously measuring two sets of atoms that experience opposite electric fields. It is projected that the experiment will be sensitive to an EDM as small as 3x10-30 e-cm, which is a 30-fold improvement over the current limit. In parallel to making the EDM experiment fully operational, the group will perform a related technological study to try to maximize the electric fields that can be sustained with the conducting oxide coated glass plates that are used. Along the way, there are two atomic polarizability measurements that the apparatus is uniquely configured to measure with improved sensitivity. Before incorporating improved field plates, the group will likely perform these measurements, which can provide tests of atomic calculations and possible improvements to the understanding of cesium clock shifts.

Quantum computing is being explored using several implementations for quantum bits (qubits) including: ions, superconducting Josephson junctions, quantum dots, photons, nitrogen vacancy centers in diamonds, and neutral atoms. Each candidate qubit has its strengths and weakness. This project will pursue several important steps towards scalable quantum computation with atoms. Neutral atoms trapped in optical lattices can be well-isolated from their environment, so they have relatively long coherence times, which is an essential feature for qubits. Trapping atoms with light presents a straightforward path for putting many qubits in the same system. This team has recently demonstrated high fidelity quantum gates involving single atoms, and has trapped exactly one atom at each of 50 lattice sites. This team will work to measure qubit states without particle loss. This team will also investigate ways to make the trapped atoms colder, which might enable new ways to entangle these atoms using collisions. Using improved methods to control and cool atoms, this team aims to dramatically improve the state of the art for entangling neutral atoms. Entanglement is an essential feature of quantum mechanics. For instance, if two identical particles can each be in either state A or B, they can be in the entangled state AA+BB, which means that the particles are in a superposition of both being in A or both being in B, while there is never one in A and the other in B. These highly non-classical states are central to the working of quantum computers. This is important because a quantum computer with >50 qubits could solve certain kinds of problems that are otherwise unsolvable.

This team will develop experimental techniques needed for a neutral atom quantum computer using cold atoms in a 3D optical lattice with 5 micron spacing between the lattice sites. They recently demonstrated perfect filling of 4x4x3 and 5x5x2 arrays, and the ability to perform single qubit gates at any site with 0.997 gate fidelity and little cross talk. For part of this grant period they will develop a new technique for measuring qubit states by coherently splitting atoms based on their internal states, and then locking them in place with a shorter length scale optical lattice. In this way their location encodes their initial internal state, which will allow them to distinguish atom loss from other errors. By dynamically switching to a deeper lattice, they will also attempt to improve atom cooling beyond the current situation with 90% of the population in the 3D vibrational ground state. If they can achieve better than 99%, it will open up the possibility of creating massive entanglement with a few collisions, which might allow for the realization of one-way quantum computing. While pursuing the above goals this team will work on demonstrating a novel form of two-qubit Rydberg gates, using a combination of ultraviolet and microwave photons. Adapting principles from their 3D addressing for one-qubit gates, they will explore ways to achieve site addressed fidelities comparable to the one-qubit gates. This would make a better quantum computer platform, and set the stage for more fully realizing the scalability potential of cold atom arrays.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

There is a long, fruitful history of precision measurements in low energy physics being used to answer questions that are usually considered the realm of high energy particle physics. For instance, precision atomic parity non-conservation experiments constrain the electroweak theory in a way that is inaccessible to particle accelerators. Another example is the search for a permanent electric dipole moment (EDM) in atoms and molecules. If an EDM were to be discovered, it would imply that the standard model of physics is incomplete, and it would point the way to a more overarching theory. The atomic measurement proposed here relates to both of these examples. The best atomic parity violation measurement uses atomic cesium in electric and magnetic fields. To extract the fundamental physics, it is necessary to disentangle the atomic physics from the atomic measurement. For about 20 years, full advantage could not be taken of the best parity violation measurement, because the atomic theory tools were not good enough. Recent theoretical advances are starting to change that, but the tools need independent validation. This project will measure a different property of cesium in an electric field, its ground state tensor polarizability (GSTP), improving the experimental knowledge of that value by a factor of at least 25. The calculations needed for the cesium parity violation result are similar to those needed to predict the GSTP, so these measurements will help validate the atomic theory with the required precision. The GSTP measurements are also similar enough to those needed for a cesium EDM search that they will be a step along the way toward completing such a measurement. The experiment will also train graduate students in a very wide range of experimental and theoretical methods.

The cesium GSTP (and ultimately the cesium EDM) will be measured using laser-cooled Cs atoms trapped in a pair of parallel 1D far-off-resonant optical lattice traps in a magnetically shielded region of space. The experiment is designed around being able to separately measure the populations of each ground state magnetic sublevel. Within the same set of atoms, direct transitions between adjacent positive magnetic sublevels can be measured at the same time as transitions between adjacent negative magnetic sublevels. In a 750 microGauss magnetic field and a 33 kV/cm electric field, these two transitions will differ by an amount that is proportional to the GSTP, ~20 Hz. The pulse-time-limited linewidth will be 1 Hz, so the line splitting that can be readily achieved with the available 108 atoms will yield ~10-4 sensitivity in a single scan. The ultimate precision will be limited by systematic affects related to the light traps. These can clearly be controlled well enough to improve on the existing 8% relative precision by a factor of 25. The fact that the new GSTP measurement directly measures transitions between ground state sublevels accounts for the large expected improvement over previous measurements, which looked for small shifts in much broader optical transitions.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

Quantum computers are built around quantum bits, or qubits. Unlike classical bits, which can be either 0 or 1, qubits can be in quantum superpositions of these two states. Furthermore, two qubits can be quantum entangled. An example of an entangled two qubit state is 00+11, where the system is in a superposition of both qubits in state 0 and both qubits in state 1. With N qubits, a system can simultaneously be in 2^N unique states at once. Such entanglement gives a quantum computer its power, allowing some properly framed problems that are intractable on classical supercomputers to be solved with as few as 60 qubits. For this project, the troup will be working on a new method to entangle neutral atom qubits, a platform that has seen the most dramatic advances in the last few years. These qubits are identical, they can be well isolated from their environment, and their internal states can be precisely controlled and measured, all critical qubit features. The experimental system is unique, in that it is possible to densely trap 3D arrays of atoms, which allows for superlative connectivity among qubits and a high density of quantum information. The entangling procedure could also be applied in more common 1D and 2D neutral atom arrays.

The group will implement a variant of a two-qubit Rydberg gate for entangling neutral atoms. One ground qubit state will be excited to a high lying Rydberg state by a two-photon transition using an ultraviolet (UV) photon and a microwave photon. This approach has most of the advantages of using a Rydberg S state, which are reduced sensitivity to photoionization and electric fields, isotropic dipole-dipole coupling, and a simple fine structure. It avoids the use of high visible light powers that can cause photoionization, spontaneous emission, and large, unwanted ac Stark shifts. The large dipole matrix element for the microwave part of the transition allows for fast gates. Although the UV plus microwave Rydberg excitation technique could be used for any neutral atom array, it will be developed here for atoms trapped in a 3D optical lattice. Toward this end, the group will implement an “anti-addressing” technique that is able to select which atoms to entangle while minimally affecting the two-qubit gate fidelity or the surrounding quantum information. The goal is for each atom to be selectively entanglable with any of 24 surrounding atoms, a very high connectivity. The gate will be implemented on significantly colder and better localized atoms than previous Rydberg gates, which should help to reach the two-qubit gate fidelity goal of 0.999. Other experimental modifications, including implementing gray molasses for the initial loading and increasing the volume of atoms that can be accessed using one and two qubit addressing techniques, will raise the number of addressable qubits in the 3D array to >250.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

Automotive and aerospace industries require lightweight, high strength materials to reduce the weight of the machines that move people and goods while maintaining their integrity. Aluminum alloys meet this need because of their high strength-to-weight ratio. The incorporation of nanosized particles in aluminum makes it stronger and more stable at elevated temperatures. These improvements can only be achieved if the nanoparticles do not agglomerate and are uniformly distributed in the aluminum matrix. This Grant Opportunities for Academic Liaison with Industry (GOALI) award aims to provide the fundamental knowledge needed to control the redistribution of particles without agglomeration. By watching the solidification process as it unfolds in real-time, quantifying the motion of the nanoparticles, and developing predictive models, the researchers plan to achieve new understanding on the processing conditions that favor a uniform particle distribution. The research results enable industry to scale-up metal matrix nanocomposite processing to commercial size castings. In addition, stronger and lighter materials enable greater fuel economy. These factors benefit U.S. economy and society. Students gain from collaboration with industry partners on the team. Outreach activities engage female and under-represented minority students in materials research, processing and manufacturing. Industry collaborator North American Die Casting Association disseminates the results to industry.

Metal matrix nanocomposites (MMNCs) offer light-weighting, improved strength, wear resistance, and high temperature stability compared to microcomposites and monolithic alloys. However, only with a homogeneous distribution of nanoparticles can the enhanced mechanical properties of MMNCs be fully realized. During solidification of MMNCs, the particles near the freezing front may be pushed or engulfed, thus impacting the final distribution of nanoparticles in the as-solidified microstructure. This project develops a comprehensive understanding of the redistribution of particles during solidification, specifically the interrelationships between particle size, fluid flow, and solidification front velocity and morphology. For this purpose, the team bridges emergent research in melt processing, real-time metrology, and phase field simulation to study in situ nanoparticle synthesis from polymer precursors and their redistribution during solidification of metal matrix nanocomposites. The team studies MMNC samples with a range of particle sizes and shapes provided by industry collaborator Eck Industries; visualizes the interactions between the nanoparticles and the solidification front in these samples via real-time X-ray imaging experiments; and conducts phase field simulations using the experimental data as input to yield detailed insights on the particle pushing-engulfment transition. This integrated effort helps to establish a morphological phase diagram, ultimately enabling precise control of the as solidified microstructure of MMNCs.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.