The interplay between light and matter is the basis of many fundamental processes and various applications1. Harnessing light–matter interactions in principle allows operation of solid state devices under new physical principles: for example, the a.c. optical Stark effect (OSE) has enabled coherent quantum control schemes of spins in semiconductors, with the potential for realizing quantum devices based on spin qubits2, 3, 4, 5. However, as the dimension of semiconductors is reduced, light–matter coupling is typically weakened, thus limiting applications at the nanoscale. Recent experiments have demonstrated significant enhancement of nanoscale light–matter interactions, albeit with the need for a high-finesse cavity6, 7, ultimately preventing device down-scaling and integration. Here we report that a sizable OSE can be achieved at substantial energy detuning in a cavity-free colloidal metal–semiconductor core–shell hetero-nanostructure, in which the metal surface plasmon is tuned to resonate spectrally with a semiconductor exciton transition. We further demonstrate that this resonantly enhanced OSE exhibits polarization dependence and provides a viable mechanism for coherent ultrafast spin manipulation within colloidal nanostructures. The plasmon–exciton resonant nature further enables tailoring of both OSE and spin manipulation by tuning plasmon resonance intensity and frequency. These results open a pathway for tailoring light–matter–spin interactions through plasmon–exciton resonant coupling in a judiciously engineered nanostructure, and offer a basis for future applications in quantum information processing at the nanoscale. More generally, integrated nanostructures with resonantly enhanced light–matter interactions should serve as a test bed for other emerging fields, including nano-biophotonics and nano-energy8, 9.
Department of Physics and Center for Nanophysics and Advanced Materials, University of Maryland, College Park, Maryland 20742, USA
Kwan Lee &
J.Z. performed all materials synthesis, and some of characterizations and measurements. Y.T. and K.L. contributed to sample characterizations. M.O. formulated the idea, performed some of measurements, wrote the manuscript, and supervised and coordinated the research. All co-authors participated in discussion and manuscript writing.