Semiconductor quantum dots are often regarded as model candidates for “qubits” –the building blocks of quantum computing - due to their discrete, atomic-like density of states and the relative ease of generating single excitations (excitons or spins) per dot. Of particular interest for quantum information processing are entanglement schemes that exploit linearly polarized exciton eigenstates that occur naturally in quantum dots due to shape anisotropy. I will show that high-resolution, polarization-resolved, resonant magneto-photoluminescence (PL) experiments1 (also known as fluorescence line narrowing) bring new insights into these exciton states in CdSe colloidal nanocrystals. Specifically, the observation of a spin-flip –like peak in the PL spectrum infers the existence of two distinct orthogonal linearly polarized excitonic states aligned along well-defined crystalline directions, which may be employed in building the coherent states needed for the practical realization of quantum computation schemes. Furthermore, similar high magnetic field photoluminescence1,2 as well as Kerr rotation spectroscopy3 experiments may be employed in studying GaN-based materials and heterostructures for more spintronics and quantum computation applications. 1 “Bright Exciton Fine Structure and Anisotropy Exchange in CdSe Colloidal Nanocrystal Quantum Dots”, M. Furis, H. Htoon, M. A. Petruska, T. Barrick, V. I. Klimov, and S. A. Crooker, submitted to PRL, arXiv:cond-mat/0511567 2 “Time and Polarization-Resolved Optical Spectroscopy of Colloidal CdSe Nanocrystal Quantum Dots in High Magnetic Fields”, M. Furis, J. A. Hollingsworth, V. I. Klimov, and S. A. Crooker, J. Phys. Chem. B 109, 15332 (2005). 3 “ Imaging Spin Transport in Lateral Ferromagnet/Semiconductor Structures”, S. A. Crooker, M. Furis, X. Lou, C. Adelmann, D. L. Smith, C. J. Palmstrøm and P. A. Crowell, Science, sept. 2005.
Moreover, high-resolution, polarization-resolved, low-temperature, single dot photoluminescence experiments independently confirm the existence of the orthogonal excitonic states in colloidal CdSe nanocrystals. Its magnitude ranges from 1 to 2meV, as a function of size, in very good agreement with the results of high field ensemble measurements.