Experimental Study of the RKKY Interaction in Multi-Quantum-Dot Systems

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*****NON-TECHNICAL ABSTRACT*****Spin, as the name suggests, is a fundamental property of electrons describing their angular momentum (as if they were spinning) and associated magnetic properties. While modern electronics predominantly use the charge of the electron to encode information, electron spin is also working for us, notably in hard drives, credit card strips, and any other magnetic storage medium. However, spin offers a much more powerful application-one that has yet to appear in any technology, but which theory has shown could lead to revolutionary improvements in computation and communication by tapping the laws of quantum mechanics. This project aims to study experimentally how information about spin orientation is conveyed between electrons in an intrinsically quantum mechanical way. Rather than investigating electrons in their natural environment, e.g., in a metal (which is difficult to probe and control), this project will fabricate artificial electronic systems from nanoscale semiconductors devices known as quantum dots, allowing far greater control over individual electrons. In quantum dots, spins can be coupled and uncoupled with the turn of a knob, as in a transistor. By constructing artificial electronic systems and investigating how spin information is communicated, the project aims to learn the limits of how long-range coupling can be used for future technologies in which programmed information is encoded in electron spin. The students working on these projects will learn skills that will enable them to become productive members of the academic or industrial communities.*****TECHNICAL ABSTRACT*****This project will explore non-local spin-spin interactions, analogs of the well-studied Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between localized spins in metals, in an artificially fabricated spin system based on gate-defined GaAs quantum dots. Particular experiments will (1) investigate the competition between RKKY and Kondo effects, aiming to shed light on less controllable counterparts of this competition in strongly correlated electronic materials, (2) explore RKKY interactions mediated by ballistic electrons or a small confined fermi sea, and (3) to observe the dephasing effects of spin coupling on the electron sea itself through weak localization measurements. A second main goal of the project is to explore the use of spin as a holder of quantum information. Because the RKKY interaction conveys spin information nonlocally it is an interesting candidate to mediate the long-range transfer of spin information for spin-based quantum information processing. However, the coupling of spins to an electron sea presumably leads to losses of quantum coherence analogous to Korringa relaxation. Experimental techniques developed in this project will determine if long-range communication of spin information using RKKY interactions are possible for future technologies. The students involved with this research will obtain the knowledge and skills necessary for future careers in academe or in industrial or national laboratories.