Solution searching devices that operate on the basis of controlling the spatiotemporal dynamics of excitation transfer via dressed photon interactions between quantum dots have been proposed. Long-range excitation transfer based on dressed photon interactions between randomly distributed quantum dots is considered to be effective in realizing such devices. Here, we successfully controlled the spatiotemporal dynamics of excitation transfer using a Y-junction structure consisting of randomly dispersed CdSe/ZnS core-shell quantum dots. This Y-junction structure has two “output ends” and one “tap end.” By exciting one output end with control light, we observed increased excitation transfer to the other output end via a state-filling effect. Conversely, we observed reduced excitation transfer to the output ends by irradiating the tap end with control light, due to excitation of defect levels in the tap end. These results show the possibility of controlling the optical excitation transfer dynamics between multiple quantum dots. 1. Introduction Light excitation in quantum dots (QDs) generates dressed photons, which are light fields localized in the vicinity of the QDs, giving rise to dressed photon interactions with other nearby matter, as well as excitation energy transfer via these interactions . In particular, various optical functional devices, such as logic gates called nanophotonic devices [2–4], light-harvesting devices , and optical signal transmitting systems [6, 7], have been realized using QDs formed of CuCl, ZnO, InAs, CdSe, and so forth, based on optical near-field excitation transfer between QDs. Nanophotonic devices have been shown to function as logic gates, such as AND, NOT, and XOR logic gates [2–4]. These devices consist of two or three closely spaced QDs having different energy levels, and by inputting a light beam serving as a power supply and another light beam serving as a control signal, excitation energy transfer between the QDs is controlled so that the light emitted from one of the QDs serves as the output. On the other hand, novel solution searching and decision making devices using a QD array provided with multiple output QDs have recently been proposed [8–10]. In these devices, by inputting control signals to the output QDs based on certain rules, the probability of the optical excitation being transferred uniformly to each QD is controlled to obtain a solution. In these operations, it is necessary to control the spatiotemporal dynamics of the optical excitation transfer between spatially distributed QDs. The features of
M. Ohtsu, T. Kawazoe, T. Yatsui, and M. Naruse, “Nanophotonics: application of dressed photons to novel photonic devices and systems,” IEEE Journal on Selected Topics in Quantum Electronics, vol. 14, no. 6, pp. 1404–1417, 2008.
T. Kawazoe, K. Kobayashi, S. Sangu, and M. Ohtsu, “Demonstration of a nanophotonic switching operation by optical near-field energy transfer,” Applied Physics Letters, vol. 82, no. 18, pp. 2957–2959, 2003.
T. Kawazoe, M. Ohtsu, S. Aso et al., “Two-dimensional array of room-temperature nanophotonic logic gates using InAs quantum dots in mesa structures,” Applied Physics B: Lasers and Optics, vol. 103, no. 3, pp. 537–546, 2011.
T. Kawazoe, K. Kobayashi, and M. Ohtsu, “Optical nanofountain: a biomimetic device that concentrates optical energy in a nanometric region,” Applied Physics Letters, vol. 86, no. 10, Article ID 103102, pp. 1–3, 2005.
W. Nomura, T. Yatsui, T. Kawazoe, M. Naruse, and M. Ohtsu, “Structural dependency of optical excitation transfer via optical near-field interactions between semiconductor quantum dots,” Applied Physics B: Lasers and Optics, vol. 100, pp. 181–187, 2010.
M. Naruse, M. Aono, S.-J. Kim et al., “Spatiotemporal dynamics in optical energy transfer on the nanoscale and its application to constraint satisfaction problems,” Physical Review B, vol. 86, Article ID 125407, 2012.
M. Aono, M. Naruse, S.-J. Kim et al., “Amoeba-inspired nanoarchitectonic computing: solving intractable computational problems using nanoscale photoexcitation transfer dynamics,” Langmuir, vol. 29, no. 254, pp. 7557–7564, 2013.
M. Naruse, H. Hori, K. Kobayashi, P. Holmstr？m, L. Thylén, and M. Ohtsu, “Lower bound of energy dissipation in optical excitation transfer via optical near-field interactions,” Optics Express, vol. 18, no. 23, pp. A544–A553, 2010.
C. Trallero-Giner, A. Debernardi, M. Cardona, E. Menéndez-Proupín, and A. I. Ekimov, “Optical vibrons in CdSe dots and dispersion relation of the bulk material,” Physical Review B—Condensed Matter and Materials Physics, vol. 57, no. 8, pp. 4664–4669, 1998.
M. Y. Valakh, Y. G. Sadfyev, N. O. Korsunska et al., “Deep-level defects in CdSe/ZnSe QDs and giant anti-stokes photoluminescence,” Semiconductor Physics, Quantum Electronics and Optoelectronics, vol. 5, no. 3, pp. 254–257, 2002.
M. Danek, K. F. Jensen, C. B. Murray, and M. G. Bawendi, “Synthesis of luminescent thin-film CdSe/ZnSe quantum dot composites using CdSe quantum dots passivated with an overlayer of ZnSe,” Chemistry of Materials, vol. 8, no. 1, pp. 173–180, 1996.