David D. Awschalom - US grants

The effects of reduced dimensionality an quantum confinement on fundamental magnetic and electronic spin dynamics are being investigated in quantum structures fabricated from II-VI diluted magnetic semiconductors (DMS). Magneto-optical spectroscopy probes spin-dependent phenomena such as carrier spin-flip scattering, spin dependent electronic tunneling and localization, magnetic polaron formation, and spin-lattice relaxation processes. The program combines state-of-the-art techniques in femtosecond optical measurements, integrated DCSQUID technology and epitaxial materials fabrication to obtain a real-timed view of dynamical behavior in quantum magnetic systems.

A 20 Tesla superconducting magnet system and a Fourier Transform Infrared (FT-IR) spectrometer will be acquired with funds from the Academic Research Infrastructure Program. The magnet system will be utilized in conjunction with the UC-Santa Barbara free-electron laser, a femto-second optical laboratory, an existing dilution refrigerator, and the FT-IR spectrometer to explore nonlinear and linear magneto-optics and magneto-transport in scientifically and technologically important systems. The research focuses on: nonlinear magneto-transport in the terahertz frequency regime associated with quantum wells and superlattices in semiconductors; saturation and relaxation in semiconductor nanostructures in large magnetic field; linear and nonlinear spectroscopy of vortex cores in high temperature superconductors; magneto-spectroscopy of self-organized quantum dots; spectroscopy of quantum wire superlattices; magneto-luminescence and magneto-absorption experiments in spin-superlattices; quantum hall effects in mesoscopic structures; and magneto-transport and the metal-insulator transition in conducting polymers. An acquired 20 Tesla superconducting magnet system, used in conjunction with a free-electron laser, a femto-second optical laboratory, an existing dilution refrigerator, and a new acquired Fourier transform infrared spectrometer, will be used to study a range of topics in the magneto-optic and magneto-transport areas concerning semiconductor superlattices, quantum wells and quantum dots as well as high temperature superconductors, one-dimensional conducting polymers, and spin superlattices.

9527553 Awschalom This interdisciplinary, two-campus project employs cutting-edge techniques from the fields of optical science and condensed matter physics. An ultra-high-vacuum scanning tunneling microscope will be used to synthesize both individual and arrays of magnetic structures directly on III-V semiconductor substrates and devices. The intrinsic magnetic behavior of the structures will be examined using microscopic Hall bar magnetometers, Aharonov-Bohm rings, ballistic transport, and high-sensitivity mechanical torque measurements. The influence of magnet particles on the spin-dependent electronic state in semiconductors will be investigated through femto-second-resolved Faraday and luminescence spectroscopes. In particular, the latter studies include spatially-resolved optical microscopy. %%% This experimental and theoretical project employs atomic-scale lithography, low-dimensional electronic transport, and ultra-fast magnetooptical spectroscopies at low temperature to investigate quantum magnetic structures. A unique aspect of the work is the in situ fabrication of "nanomagnets" only a few dozen atoms in diameter, whose optical and magnetic properties will be investigated. The work encompasses semiconductor physics, optics, and magnetism. The training gained by students in the areas of optical science and engineering will prepare them for a wide spectrum of career opportunities. The nanosize magnetic semiconductors exhibit novel magnetooptical phenomena that are currently incompletely understood, but which are felt to have great potential as possible device structures. ***

9701072 Awschalom This experimental effort is aimed at understanding fundamental aspects of coherent electronic spin dynamics and spin-related transport in artificial quantum structures. Such investigations form the basis for the exploitation of coherent spin transport in future generations of magneto-electronic devices. The experiments focus on model nanostructures fabricated from II-VI magnetic semiconductors (MS), allowing one to systematically tailor spin interactions between confined electronic states and low dimensional distributions of local moments. The project is comprised of highly interactive efforts that combine the concurrent development of sophisticated MS nanostructures (digital magnetic heterostructures, magnetic two-dimensional electron gases (2DEGs), and quantum spin dots) with state-of-the- art spin dynamical probes having high temporal (~100 fs) and spatial (~100 nm) resolution (femtosecond Faraday rotation and time-resolved near-field scanning optical microscopy) and low- temperature magnetotransport. %%% Recent decades have witnessed the development of sophisticated solid state fabrication techniques that enable the construction of artificial atomic architectures ("nanostructures") in which one or more dimensions are at the nanoscale (a billionth the diameter of a human hair). There has also been a concurrent development of optical measurement techniques that allow one to record physical phenomena at unprecedently high speeds (ultrafast spectroscopy) and with very high spatial definition (near field microscopy). In this highly interactive project, we employ a powerful combination of state-of-the-art fabrication and measurement techniques to study the dynamic motion of electrons in new classes of "magnetic nanostructures," wherein magnetic atoms are embedded within an engineered semiconductor. These fundamental investigations lay the groundwork for future generations of magneto-electronic devices that would exploit the quantum mecha nical interactions between electrons and magnetic atoms for high-speed communication devices and ultra-high density memories. ***

9871849 Metiu We plan to synthesize and assemble dilute magnetic semiconductor nanostructures and study their transport and optical properties by using near field optical microscopy. It is well known that by reducing the size of a semiconductor structure we can affect and control the properties of the electrons in it. We know practically nothing about the way in which this size reduction affects the magnetic properties of these systems, even though we expect these effects to be considerable. We will prepare nanocrystalline "dots" of II-VI semiconductor doped with divalent transition metal ions with magnetic properties (Mn(II), Cr(II), Fe(II) and Cu(II) ). We can thus study the effect of confinement on the exchange interactions and the magneto-optical properties of these materials. We plan to use a near field microscope to perform femtosecond and cw studies of the magneto-optical properties of individual dots and to determine how these properties depend on dot sizes. We also plan to create ensembles of such dots so that we can study the collective effects created by the interaction between the dots. One of our most important tools is the near field optical microscope. This is a wonderful tool with many exciting uses, but the quantitative interpretation of the measurements is hampered by the lack of a quantitative theory of the electromagnetic fields produced in the structure being studied. We propose to develop new theoretical methods for solving this problem. %%% The kind of studies proposed here are motivated by the need of making smaller electronic devices and denser computer memories. As the elements of these devices become smaller the properties of the electrons in them are being modified. We cannot design these devices if we cannot anticipate and understand how the electrons in them will behave. Our work hopes to fill this gap in our understanding. The ultimate computer will be a device in which the electrons themselves are computing elements. The main candidates right now are systems in which various spin states are being excited, since they maintain the information imparted to them (coherence) for the longest time. This is one additional reason why the study of spin behavior in small structures may impact future technologies.

This award is being supported by the Office of Multidisciplinary Activities; the Division of Materials Research, Directorate for Mathematical and Physical Sciences; and the Division of Electrical and Communications Systems, Directorate for Engineering.***

9980734
Cleland

The PI's have recently developed methods by which deep sub-micron-size mechanical structures, with integrated displacement-inducing and displacement-sensing elements, can be fabricated and used as practical sensors. The PI's wish to apply this technology to the development of high-frequency chip-based magnetic sensors, which in the ultimate limit will be sensitive to the behavior of individual magnetic moments. The sensors they will develop will be based on nanometer-scale, radiofrequency cantilevers, fabricated from single-crystal GaAs heterostructure substrates. GaAs is a piezoelectric material, allowing the use of both piezoresistive and piezoelectric strain sensing. The magnetic signals will emanate either from magnetic samples embedded in the sensor geometry, or from the interaction of an magnetic tip integrated in the cantilever design, which is scanned over a fixed, magnetically active sample. In the former geometry, they plan experiments to probe the physics of very small ferromagnetic and paramagnetic samples, and the mechanical detection of optically-induced electronic and nuclear magnetization. The latter geometry will allow a number of microscopy applications, probing both surface and subsurface interactions. Signals emanating from subsurface sources, such as electric currents on a buried heterostructure interface, would allow imaging on an otherwise topologically featureless sample.

These sensors should be able to probe time scales approximately four orders of magnitude shorter, and magnetic volume scales approximately five orders of magnitude smaller, than the present state-of-the-art in scanned magnetic force probes and fixed torque magnetometry. These sensors should allow sensitivities of order one Bohr magneton at frequencies approaching 1 GHz. The high frequencies and small physical size scales they will thereby be able to probe will engender a number of interesting engineering and science applications.
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This experimental project explores collective and coherent spin behavior of electrons, local moments and nuclear spins in low dimensional systems ranging from 2D electron gases to 0D quantum dots. The experiments focus on model nanostructures fabricated from II-VI magnetic semiconductors which can be systematically tailored to modulate spin interactions between confined electronic states, magnetic ions and nuclei. The project combines development of sophisticated nanostructures and state-of-the-art spin probes having high temporal (~100 fs) and spatial (~100 nm) resolution, and high magnetic moment sensitivity (~105 Bohr magnetons). Microfabricated cantilevers will be used to search for collective spin effects in magnetic semiconductor nanostructures. Dynamical spin organization in these nanostructures will be studied using an "all-optical" magnetic resonance technique, encompassing spin precession of electrons, local moments and nuclear spins. Coherent optical spectroscopy coupled with time-resolved transport will probe dynamical spin transport in mesoscopic systems (wires) wherein the nuclear polarization is systematically varied using optical pumping. Finally, near field scanning optical resonance techniques will be developed to achieve spatially resolved magnetic resonance imaging of 2D electron spin systems. Knowledge of the collective spin response in nanostructures gained from this project may be important for coherent control of spin processes in future generations of magneto-electronic devices. Advanced technical training in solid state physics, materials science, and advanced instrumentation will prepare students for careers in academic and industrial environments.
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This experimental condensed matter physics project explores the complex quantum mechanical behavior of electrons, magnetic atoms and nuclei in low dimensional systems ranging from "electron sheets" (2D electron gases) to "electron boxes" (0D quantum dots). The experiments use model nanostructures fabricated from a family of materials (II-VI magnetic semiconductors) in which the quantum mechanical property known as "spin" can be systematically varied. A fundamental understanding of spin transport in nanostructures may enable new technologies based on quantum mechanical interactions in the solid state. The project is comprised of a collaborative effort that combines development of sophisticated nanostructures with state-of-the-art spin probes having high temporal (~100 femtoseconds) and spatial (~100 nanometer) resolution, and high spin sensitivity (~ 105 magnetic atoms). Experiments range from ultrasensitive magnetometry, to "all-optical" spin resonance microscopy, to dynamical studies of electron spin transport. While the principal focus is on fundamental physics, knowledge gained will be important for developing concepts in the coherent control of spin processes in future generations of high speed magneto-electronic devices, with potential applications ranging from ultrafast switching to quantum computation. This research involves advanced technical training in materials physics and advanced instrumentation, and prepares students to make immediate contributions both in academic and industrial environments.

This proposal is a collaborative experimental effort that explores the coherent spin dynamics of electrons, ions and nuclear spins in low dimensional systems that confine electrons and/or photons. The proposed experiments focus on model nanostructures fabricated from both conventional and magnetic II-VI and III-V semiconductors and exploit the unique opportunities offered by such systems to systematically tailor spin interactions between confined electronic states, magnetic ions, and nuclei. The project combines state-of-the-art spin dynamical probes having high temporal (~100 fs) and spatial (~100 nm) resolution with sophisticated materials engineering of a variety of semiconductor-based structures whose dimensions span the nano- to the mesoscale. The overall thrust of this research program is to develop a fundamental understanding of the control, transport and storage of coherent spin phenomena in semiconductors via optical experiments that probe spatio-temporal spin transport in heterostructures, coherent spin control in optical microcavities, coherent nuclear spin dynamics in isotopically-engineered nanostructures, and coherent spin excitations in mesoscopically patterned ferromagnets. These experiments potentially have a broad and long range impact on future technologies that explicitly use quantum phenomena for new functionality. The research provides students with advanced technical training in leading edge materials engineering and condensed matter techniques. The principal investigators will disseminate the results of their scientific activity to the general public, and continue to attract a diverse and talented student base.

A fundamental understanding of the transport, storage and manipulation of coherent spin states in semiconductors is important for the future development of quantum information science and technology. Contemporary materials fabrication techniques offer access to important model systems in this context by enabling the systematic tailoring of spin interactions between confined electronic/photonic states and magnetic ions/nuclei. This collaborative proposal is aimed at using ultrafast and high-spatial resolution optical techniques to probe coherent electronic, ionic and nuclear spin dynamics in a variety of semiconductor-based architectures with dimensions spanning from the nano- to the mesoscale. The project will address basic issues such as coherent spin transport in complex heterostructures, coherent spin control in optical microcavities, coherent nuclear spin dynamics in isotopically-engineered nanostructures, and coherent spin excitations in ferromagnetic semiconductor nanostructures. It is anticipated that this project will result in important fundamental insights into questions that are at the very forefront of condensed matter physics and simultaneously have a broad and long range impact on future technologies that explicitly use spintronics or quantum phenomena for new functionality. The research provides students with technically sophisticated training in the synthesis of semiconductor and magnetic nanostructures, ultrafast optical spectroscopy, low temperature transport, and micromagnetometry, and is hence an ideal training ground for both academic and industrial environments. The principal investigators will disseminate the results of their scientific activity to the general public, and continue to attract a diverse and talented student base.

The Fourth International School and Conference on Spintronics and Quantum Information Technology continues a tradition starting with Spintech I (Maui, 2001), and continuing with Spintech II (Brugge, 2003) and Spintech III (Osaka, 2005). Spintech IV will highlight both fundamental physical phenomena related to spin-dependent effects in semiconductors as well as advances in the development of new types of semiconductor spintronic materials and devices. This includes the current understanding of spin related
behavior in (magnetic) semiconductor and hybrid magnetic/semiconductor structures and the prospects of exploiting these phenomena in future electronic, magnetic, or optical applications. The Spintech IV school will take place during the first half of the week to orient graduate students and new researchers to this emerging and exciting field. The Spintech IV conference will take place during the second half of the week and will be aimed at stimulating rapid progress in the fabrication, measurement, and theory of semiconductor spintronic systems. Participants will tackle the new challenges for materials and nanostructure designs that have emerged from measurements and calculations in this field, including electron and nuclear spin coherence times, electronic spin transport, measurement fidelity, and exchange interaction strength.

The requested funds will be used support approximately 22 Graduate Students for their attendance and participation in the Fourth International School and Conference on Spintronics and Quantum Information Technology in Maui, Hawaii

Technical
The past decade has witnessed rapid advances in the development of "semiconductor spintronics," an area of research that broadly aims to exploit electron spin for qualitatively new semiconductor device functionality of both semi-classical and quantum character. This collaborative project is aimed at harnessing recent fundamental discoveries in semiconductor spintronics (such as the spin Hall effect and the enhancement of spin coherence in micro-resonators) for the systematic control of coherent spin phenomena in micro-patterned semiconductor devices. We will develop static and dynamical electrical measurements of the spin Hall effect as well seek pathways for enhancing the magnitude of this phenomenon. We also intend to pursue investigations that explore the entanglement and coherent manipulation of spins in coupled optical microcavities, with the ultimate goal of coherently controlling a single spin. Finally, we will conduct experiments that exploit the exchange interaction across interfaces for coherent spin control in both paramagnetic and ferromagnetic semiconductor heterostructures. Methods of investigation include spatially-resolved femtosecond optical spectroscopies, variable-temperature magnetotransport, direct magnetization, scanning probe microscopies, molecular beam epitaxial growth, and submicron fabrication techniques. The project is an integrated effort between the two principal investigators, emphasizing fundamental discovery in condensed matter physics, but with a clear eye on phenomena that could be of potential importance for future information technologies. The project combines sophisticated measurement techniques with advanced materials engineering, thus providing cutting edge training in both fundamental physics and materials science for undergraduate and graduate students.

Non-technical
Contemporary information technology relies on the charge of electrons for computation (logic) and the magnetic properties called spin of electrons for permanent storage. The past decade has witnessed rapid advances in the development of "semiconductor spintronics," an area of research that broadly aims to integrate these traditionally separate functionalities. This proposal is aimed at the fundamental frontiers of semiconductor spintronics, where we seek to control the behavior of electron spin in microscopically patterned semiconductor chips. By exploiting the consequences of special relativity in solid state crystals, we will develop electrical means of probing and harnessing the "spin Hall effect," a contemporary spin analog of the classical Hall effect discovered over a century ago. Enhancing our fundamental understanding of the spin Hall effect may allow us to envision new classes of spintronic devices that exploit the non-intuitive laws of quantum physics for new types of logic without the need for magnetic fields or magnetic materials. We also intend to develop experiments that explore the quantum control of spins in finely tuned "micro-resonators," micron sized "boxes" that trap light and thus enhance its interaction with the spin of electrons. Our ultimate goal is the quantum mechanical control of a single electron spin in such boxes, enabling both computation and optical communication in a single device. Finally, we will develop experiments that exploit the interaction between magnetic ions and itinerant electrons across exquisitely designed interfaces. The project is an integrated effort between the two principal investigators, emphasizing fundamental discovery but with a clear eye on phenomena that could be of potential importance for future information technologies. The project combines sophisticated measurement techniques with advanced materials engineering, thus providing cutting edge training in both fundamental physics and materials science for undergraduate and graduate students.

****Technical Abstract****
The emerging area of "quantum information science" has seen rapid advances in exploiting the coherent control of single spins in defect centers in diamond and SiC, opening up a new pathway toward qubits that function at room temperature. This proposal aims to extend these remarkable developments toward the coherent manipulation and full state transfer of quantum information in heterogeneous systems built from disparate materials whose individual quantum properties are already well understood. The ultimate goal is to achieve quantum-coherent communication between physically distinct quantum systems at the single spin level and at room temperature. The PIs will combine spatio-temporally resolved single spin spectroscopies with the design and fabrication of model systems that couple single spins (such as defects in SiC) with ensemble spins in low dimensional communication channels (such as 2DEGs and nanowires). The proposed research offers advanced technical training in quantum materials and measurement and provides ideal training for future careers in academics and industry. The PIs will also enhance the diversity and excellence of undergraduate research through institutional programs and by collaboratively teaching a cross-disciplinary undergraduate course on the Practice of Science.

****Non-Technical Abstract***
Modern information technology relies on devices such as lasers, flash memory and magnetic tunnel junctions that exploit the quantum mechanical aspects of the natural world. Such device technologies still do not make use of the full technological potential of quantum mechanics, restricting their functionality to control over the amplitude of quantum mechanical waves and ignoring their phase. The emerging area of "quantum information science" seeks to redress this limitation by exploring the technological possibilities of the more non-intuitive aspects of quantum mechanics, namely quantum coherence and quantum entanglement. A key challenge for quantum information processing is the development of pragmatic scenarios that will allow the exchange of coherent quantum information between disparate parts of a system. This proposal aims to demonstrate such phenomena in heterogeneous systems built from disparate materials whose individual quantum properties are well understood. The ultimate goal is to achieve quantum-coherent communication between physically distinct quantum systems at the single spin level and at room temperature. The proposed research offers advanced technical training in quantum materials and measurement and provides ideal training for future careers in academia and in industry. The PIs will also enhance the diversity and excellence of undergraduate research through institutional programs and by collaboratively teaching a cross-disciplinary undergraduate course on the Practice of Science.

Non-Technical Abstract:
Quantum Information Science and Engineering (QISE) has made remarkable progress, heralding promise for revolutionary new technologies in quantum sensing, communication, computation and cryptography. Recent advances bring the promise of QISE into marketable technologies with the potential for a sustained and profound societal impact. A successful technology leap requires investment in a trained workforce adept in the basic quantum sciences as well as proficient in the necessary engineering fields, informed about the broader issues of developing quantum science into marketable quantum devices. This is an optimal time to explore new, more effective ways of coupling academic and industrial research programs, promoting convergence of disciplines, resources and sectors in this endeavor. This project addresses these issues by developing a series of workshops constituting the QISE Network (QISE-NET): a community of tightly integrated university-industry partners, focused on leading-edge QISE projects. These associates comprise three-person teams of university faculty, industrial researchers, and a graduate student serving as the pivotal component of the group. QISE-NET serves as a model for a new approach to graduate student education as well as truly collaborative university-industry interactions, including the selection of projects, yearly workshops, and student mentoring activities. The program creates new employment opportunities for students along with company positions and start-up ventures. This Project promotes Convergence by offering a way to educate, train and nurture a cohort of industry-academia partnerships between the convergent disciplines of Materials Science Theory, Materials Science Experiment, Device Engineering, Physics, Chemistry, Computer Science, and Industrial Research.

Technical Abstract:
This activity helps to create a distinctive and critically-needed intellectual infrastructure for students studying the convergent QISE disciplines. By linking the talents, resources and approaches of both the academic and industrial environment, QISE-NET is able to create and leverage an intellectually broad community of researchers to generate the new science, engineering and marketable QISE technologies of the future. By demonstrating how students' academic work can be enabled and broadened through access to the resources, systems and team-based approaches available in industrial research laboratories, QISE-NET establishes new models of university-industry collaboration, while providing a more cogent program for graduate student education in QISE. Proposals are submitted through a program website, and announced using broad electronic distribution through academic and professional society organizations, as well as through corporate network distribution. They are evaluated by an external advisory board consisting of academic and industrial researchers spanning a broad range of science and technology. Yearly workshops form the principal means of communications among the various projects and serve to knit the network. Participants share research results, and understand the different best practices that produce effective interactions. An education specialist from a NSF center conducts independent, anonymous assessments from the participants, and provides a mechanism to improve the effectiveness of both the program and workshops. The QISE-NET will generate outstanding, leading-edge scientific results with applicability to new, marketable technologies, and serve to strengthen collaborations between academia and industry. This Project promotes Convergence by offering a way to educate, train and nurture a cohort of industry-academia partnerships between the convergent disciplines of Materials Science Theory, Materials Science Experiment, Device Engineering, Physics, Chemistry, Computer Science, and Industrial Research.

Quantum sensing has the potential to revolutionize understanding of the inner workings—the molecular underpinnings—of biology and human health. Quantum sensing will allow probing the physical properties of biological systems with nanometer resolution and single-molecule sensitivity, resolving the microscopic relationships among ions, molecules, cells, and tissues while also elucidating dynamics. The Institute for Quantum Sensing in Biophysics and Bioengineering will create new types of biocompatible quantum sensors and embed these quantum sensors within biological systems to extract new information and gain control over biological processes that, until now, have been beyond reach. The Institute brings together researchers from materials science, physics, chemistry, engineering, biology, and medicine working side-by-side at every step to define and tackle these manifestly interdisciplinary challenges.

The Institute will train the future quantum technology workforce by creating a Quantum Academy (for K-12) and Quantum Institute (post-secondary workforce training). These programs will work with underserved communities within Chicago, exposing students to quantum science and training teachers in the development of quantum science curriculum. These programs seek to show students not only the material, but also the scientific process, to help them understand quantum science and see themselves as scientists. The programs also will match trainees with potential employers in quantum technology fields.

The Quantum Leap Challenge Institute for Quantum Sensing in Biophysics and Bioengineering will develop biocompatible quantum materials, establish protocols for quantum sensing and imaging within cells, and demonstrate the utility of quantum measurements in biology and medicine. The research is focused on four thrusts. In the sensing thrust, this project will define novel biocompatible probes to enable quantum measurements that are correlated in time and/or space. In the biological targeting thrust, material compatibility and biochemical specific targeting will be ensured, and sensing protocols will be developed to overcome issues related to integrating quantum sensors into living cells. In the correlative imaging thrust, the Institute will develop controlled test cases, image processing techniques, and reconstruction tools that exploit both classical and quantum correlations for imaging biological systems. Importantly, these three thrusts are tightly connected to a fourth thrust centered on biophysical and biological grand challenges to help image dynamics in ion channels, force networks, bioelectricity, and cellular communication.

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.