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While resonances abound in classical physics, quantum superposition yields unique manifestations of resonant behavior, most notably in the case of Fano resonances (FRs). Originally revealed in atomic scattering, but inherent also to the solid state, FRs arise from the coupling of a continuum to a discrete quantum state, thus providing interfering pathways for some transition. While FRs have been studied for more than half a century, Fano also predicted the possibility of "multi-state" resonances, in which multiple states mutually interact through a common continuum. Such behavior is rare, however, with "q-reversal" due to intruder-states in Rydberg atoms, in which the FRs of a given Rydberg manifold are modified by other manifolds in the same energy range, being most notable. Although this phenomenon is a single-atom effect, whose states arise within the same atom, in this talk I demonstrate a very different multi-state FR, involving distinct states formed on separate nanostructures that interfere with each other through a connecting continuum. While each of these states contributes to a FR due to its own continuum coupling, tuning them near coincidence gives rise to an avoided crossing, indicating the formation of an extended molecular system that is "bonded" via the continuum. This remote interaction is shown to be significantly more robust than the direct level hybridization typical of coupled quantum dots, a feature we attribute to the very different character of the coupling in our system. While in quantum-dot molecules the coupling arises from direct wavefunction overlap at a common tunnel barrier, in our case it is mediated through a degenerate continuum. Although often viewed as a source of decoherence, our work instead shows how such a continuum may be essential to support coherent interactions, a result that could allow new approaches to engineer the collective states of nanostructures. Y. Yoon, M.-G. Kang, P. Ivanushkin, L. Mourokh, T. Morimoto, N. Aoki, J. L. Reno, Y. Ochiai, and J. P. Bird, "Non-local bias spectroscopy of the self-consistent bound state in quantum point contacts near pinch-off", Appl. Phys. Lett. 94, 213103 (2009) Y. Yoon, M.-G. Kang, T. Morimoto, L. Mourokh, N. Aoki, J. L. Reno, J. P. Bird, and Y. Ochiai, "Detector backaction on the self-consistent bound state in quantum point contacts", Phys. Rev. B 79, 121304(R) (2009) Y. Yoon, L. Mourokh, T. Morimoto, N. Aoki, Y. Ochiai, J. L. Reno, and J. P. Bird, "Probing the microscopic structure of bound states in quantum point contacts", Phys. Rev. Lett. 99, 136805 (2007) Work performed in collaboration with: Y. Yoon, M.-G. Kang, T. Morimoto, M. Kida, N. Aoki, J. L. Reno, Y. Ochiai, J. Fransson, and L. Mourokh Work supported by: Department of Energy (DE-FG03-01ER45920) |
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