New technologies based on the exploitation of so-called “second order” quantum phenomena – such as quantum entanglement – deserve a public-friendly, rational, and sexy name. Spookytechnology is that unifying term. From historical and motivational perspectives, this name has greater value than the many variations of quantum this and quantum that presently used. As many already believe, the pursuit of spookytechnology has profound implications for the development of the physical and information sciences and ultimately for society at large. Spookytechnology will find its place in the increasingly dense line of major technological revolutions of our time: quantum, info, bio, nano, spooky.
Nature Physics 3, 41 (2007)
Silicon has many attractive properties for quantum computing, and the quantum dot architecture is appealing because of its controllability and scalability. However, the multiple valleys in the silicon conduction band are potentially a serious source of decoherence for spin-based quantum dot qubits. Only when these valleys are split by a large energy does one obtain well-defined and long-lived spin states appropriate for quantum computing. Here we show that the small valley splittings observed in previous experiments on Si/SiGe heterostructures result from atomic steps at the quantum well interface. Lateral confinement in a quantum point contact limits the electron wavefunctions to several steps, and enhances the valley splitting substantially, up to 1.5 meV. The combination of electronic and magnetic confinement produces a valley splitting larger than the spin splitting, which is controllable over a wide range. These results improve the outlook for realizing spin qubits with long coherence times in silicon-based devices.
Nanotechnology as a social concept and investment focal point has drawn much attention. Here we consider the place of nanotechnology in the second great technological revolution of mankind that began some 200 years ago. The so-called nanotechnology revolution represents both a continuation of prior science and technology trends and a re-awakening to the benefits of significant investment in fundamental research. We consider the role the military might play in the development of nanotechnology innovations, nanotechnology’s context in the history of technology, and the global competition to lead the next technological revolution.
Manufacturing materials and systems with components thousands of times smaller than the width of a human hair promises vast and sometimes unimaginable advances in technology. Yet the term nanotechnology has formed as much from people’s expectations as from scientific reality. Understanding the creation and context of this social construction can help us appreciate and guide what may be a burgeoning revolution. This chapter considers what different groups are referring to when they say nanotechnology, how this relates to the science involved, and how the various definitions of this broad field of endeavor might be improved. The ramifications and implications of these seemingly innocuous naming choices are also discussed. Although in many respects nanotechnology serves as cover justification for increased spending in the physical sciences, at present it is the most hopeful route to solving some of the planet’s greatest problems.
preprint; Chapter in Advances in Computers 71:Nanotechnology, edited Marvin Zelkowitz, Elsevier, 2007 Identifying Nanotechnology in Society Charles Tahan Cavendish Laboratory, University of Cambridge, JJ Thomson Ave, Cambridge, CB3 0HE, UK charlie@tahan.com (2006) Manufacturing materials and systems with components thousands of times smaller than the width of a human hair promises vast and sometimes unimaginable advances in […]
Phys. Rev. B 75, 115318 (2007)
We present an effective mass theory for SiGe/Si/SiGe quantum wells, with an emphasis on calculating the valley splitting. The theory introduces a valley coupling parameter, $v_v$, which encapsulates the physics of the quantum well interface. The new effective mass parameter is computed by means of a tight binding theory. The resulting formalism provides rather simple analytical results for several geometries of interest, including a finite square well, a quantum well in an electric field, and a modulation doped two-dimensional electron gas. Of particular importance is the problem of a quantum well in a magnetic field, grown on a miscut substrate. The latter may pose a numerical challenge for atomistic techniques like tight-binding, because of its two-dimensional nature. In the effective mass theory, however, the results are straightforward and analytical. We compare our effective mass results with those of the tight binding theory, obtaining excellent agreement.
STS 201: Nanotech+Society An undergraduate course taught in the spring semester of 2005 at the University of Wisconsin-Madison. A non-technical, discussion-based introduction to nanotechnology and science and technology studies. Nanotechnology and Society: A discussion-based undergraduate course. (preprint, published PDF, scitation access in Am. J. Phys., 74, 443, 2006) Talks 1. Teaser introduction to nanotech with some consideration of […]
Nature Physics, 2, 856, 2006
Recently, condensed matter and atomic experiments have reached a length-scale and temperature regime where new quantum collective phenomena emerge. Finding such physics in systems of photons, however, is problematic, as photons typically do not interact with each other and can be created or destroyed at will. Here, we introduce a physical system of photons that exhibits strongly correlated dynamics on a meso-scale. By adding photons to a two-dimensional array of coupled optical cavities each containing a single two-level atom in the photon-blockade regime, we form dressed states, or polaritons, that are both long-lived and strongly interacting. Our zero temperature results predict that this photonic system will undergo a characteristic Mott insulator (excitations localised on each site) to superfluid (excitations delocalised across the lattice) quantum phase transition. Each cavity’s impressive photon out-coupling potential may lead to actual devices based on these quantum many-body effects, as well as observable, tunable quantum simulators. We explicitly show that such phenomena may be observable in micro-machined diamond containing nitrogen-vacancy colour centres and superconducting microwave strip-line resonators.
Thesis, 2005, University of Wisconsin-Madison
Semiconductor architectures hold promise for quantum information processing (QIP) applications due to their large industrial base and perceived scalability potential. Electron spins in silicon in particular may be an excellent architecture for QIP and also for spin electronics (spintronics) applications. While the charge of an electron is easily manipulated by charged gates, the spin degree of freedom is well isolated from charge fluctuations. Inherently small spin-orbit coupling and the existence of a spin-zero Si isotope facilitate long single spin qubit coherence times. Here we consider the relaxation properties of localized electronic states in silicon due to donors, quantum wells, and quantum dots, including effects due to phonons and Rashba spin-orbit coupling. Our analysis is impeded by the complicated, many-valley band structure of silicon and previously unaddressed physics in silicon quantum wells. We find that electron spins in silicon and especially strained silicon have excellent decoherence properties. Where possible we compare with experiment to test our theories. We go beyond issues of coherence in a quantum computer to problems of control and measurement. Precisely what makes spin relaxation so long in semiconductor architectures makes spin measurement so difficult. To address this, we propose a new scheme for spin readout which has the added benefit of automatic spin initialization, a vital component of quantum computing and quantum error correction. Our results represent important practical milestones on the way to the design and construction of a silicon-based quantum computer.
Am. J. Phys. 74, 4 (April 2006)
Nanotechnology has emerged as a broad, exciting, yet ill-defined field of scientific research and technological innovation. There are important questions about the technology’s potential economic, social, and environmental implications. We discuss an undergraduate course on nanoscience and nanotechnology for students from a wide range of disciplines, including the natural and social sciences, the humanities, and engineering. The course explores these questions and the broader place of technology in contemporary societies. The course is built around active learning methods and seeks to develop the students’ critical thinking skills, written and verbal communication abilities, and general knowledge of nanoscience and nanoengineering concepts. Continuous assessment was used to gain information about the effectiveness of class discussions and enhancement of student understanding of the interaction between nanotechnology and society.
