Collaborative Research: Spin-electronic Dynamics in Three Terminal Couples Quantum Structures

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Eric I. Altman, Yale University"Spin-electronic Dynamics in Three Terminal Coupled Quantum Structures"This project focuses on exploring enabling technologies to allow the spin degree of freedom to be used as the controlling mechanism for quantum communication and computing. The principal investigators will fabricate and study coupled quantum-dot (QD) systems consisting of closely spaced III-V semiconductor, gallium arsenide (GaAs) quantum dots controlled by separated electrodes. The systems will be designed to transmit spin charges into QDs and to couple them in the neighboring dots by exchange interaction. Such a system is the first step toward building quantum logic gates, because the spin of one dot affects the electronic charge transport in the other dots by the exchange coulomb blockage effect. The spin states and the degree of coupling between the quantum dots can also be controlled by applied magnetic and/or electric fields. Magnetic contacts will serve as spin sources to provide carriers with particular spin orientation. The tunneling of these carriers through a particular dot will depend on the available spin state in the dot. This provides a convenient and practical way of determining the spin orientation of a particular dot and thus the variation of the spin in this dot after a certain time interval. Studying the spin dynamics in the context of manipulating and controlling individual spin states in each dot, and collectively in coupled quantum dots provides basic technology for fabricating quantum transistors and logic gates for quantum computing and communication devices. Successful fabrication of coupled dot systems requires employing state of the art synthetic methods at SUNY Binghamton. The fabrication of electrode structures at nanometer scales will use lithography on metallic thin films. The preparation of semiconductor quantum dots, such as GaAs, in the nanometer scales will utilize various synthetic, processing and assembling strategies. Methods will also be developed to produce GaAs:Mn nanoparticles; the manganese (Mn) doping can enhance spin state operating temperature in quantum dots. These semiconductor nanoparticles will be characterized using spectroscopic and microscopic techniques at both Yale and Binghamton. The spin charge exchange interaction between neighboring QDs will be studied by producing highly monodispersed III-V semiconductor nanoparticles self-assembled in a narrow gap about hundreds of nanometers wide between two metallic electrodes made by lithography. The study of detailed tunneling characteristics as a function of temperature and bias will be carried out in a magnetic cryostat at Binghamton. At Yale, scanning tunneling microscopy will be used to characterize the size, morphology, and electronic properties of the nanoparticles and their positioning between the electrodes. Magneto-infrared spectroscopy will be carried out on self-assembled semiconductor nano-particle arrays to examine spin exchange coupling between QDs. Broader Impact: This research will strongly impact future technologies in new functional devices based on spin degree of freedom, particularly providing assistance to the development of three-terminal spin field-effect-transistors using the developed techniques. These activities will allow the graduate students involved to learn and prepare themselves to become future technologists for developing next generation communication and computing devices. The integration of the nanostructure and novel computing technology into the curricula will provide interdisciplinary experiences for better career training for the students involved.