Real-Time Electron Dynamics in Nanoscale Structures

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Nanoscale electrical structures exhibit numerous interesting phenomena such as the Coulomb blockade or quantum coherence. Such phenomena have traditionally been studied using dc or quasi-dc measurement techniques, even though the underlying electron dynamics take place on much shorter time scales. While such measurements provide a tremendous amount of information, much more could be accessed by studying the dynamics of individual electrons. For instance, temporal correlations in electron tunneling are expected in transport through Coulomb blockade nanostructures, but have never been observed directly. This Individual Investigator Award supports a project that addresses such issues by using a radio-frequency single-electron transistor to study the motion of individual electrons in a quantum dot. Doing so will ultimately allow investigation of electronic correlations and quantum coherence on time scales of tens to hundreds of nanoseconds. A series of experiments on both single and double quantum dots will be undertaken, with the goal of studying electron correlations by means of their counting statistics and probing quantum coherent phenomena on their intrinsic time scales. The techniques used in these experiments are also relevant to the qubit readout problem in quantum computation, and are expected to shed light on the quantum measurement problem in general. This effort involves use of cutting-edge techniques in nanofabrication and radio-frequency characterization, as well as cryogenic and low noise techniques, providing the students involved with skills valuable in either academia or industry.For many nanoscale structures (whose physical dimensions are measured in billionths of a meter), the motion of individual electrons plays an important role in their electrical characteristics. While the roles of individual electrons and the interactions between them have long been recognized, electrical transport in nanostructures is usually probed by measuring the average conductance. Although such measurements have provided a tremendous amount of information, much more could be accessed by studying the dynamics of individual electrons. This Individual Investigator Award supports a project that addresses such issues by using a fast and very sensitive electrometer known as a radio-frequency single electron transistor to study the motion of individual electrons on a semiconductor quantum dot. By observing the motion of individual electrons in a current driven through the dot, for instance, it will be possible to extract additional information about how electrons interact in nanostructures. Because electrons are quantum-mechanical objects, the research will also focus on how the process of observing the electron motion affects the motion itself. This problem, which is also important for measurement of a qubit in quantum computation, is related to the question of how quantum mechanical objects lose their wave-like properties (their quantum coherence) when affected by a macroscopic object. The ability to measure individual electrons on short time scales (millionths of a second or less) should shed new light on such issues. This effort involves use of cutting-edge techniques in nanofabrication and radio-frequency characterization, as well as cryogenic and low noise techniques, providing the students involved with skills valuable in either academia or industry.