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Detection and Coherent Manipulation of Valley States of Individual Electrons in Silicon

November 17, 2016 -
2:00pm to 3:30pm
HongWen Jiang

Valley states of electrons in silicon represents another degree of freedom in addition to spin and charge degree of freedoms. The characterization and control of the valley degree of freedom in nanostructure silicon presents a major challenge, as the characteristics of valleys depend on the microscopic details of interface and electrical confinement etc. In this talk, I discuss methods to detect and to coherent manipulate valley states of individual electrons in gate defined Si quantum dots, as they are becoming leading candidates for semiconductor qubits. Our electron spin resonance spectroscopy experiment has revealed a unique aspect of the spin-valley interaction. An unexpected anti-crossing of the driven dot energy levels is observed when the Zeeman and valley splitting coincide. The detected anti-crossing provides a direct measure of spin and valley mixing, facilitated by spin–orbit interaction in the presence of non-ideal interfaces. In another experiment, coherent evolutions between two valley states is excited by a fast electrical pulse and the results are projected as the occupations of two different charge states for read-out. The dependence of coherent oscillations on pulse excitation level and duration allow us to map out the energy dispersion of the valleys. Ramsey-fringe experiment shows an unprecedentedly long phase coherence time. Evidently, the additional valley states alter the dispersion of the nanostructure which give rise to a desirable property to against charge noise of the environment. 

Hosted by Jacob Taylor.

1201 John S. Toll Physics Bldg.