|About this Abstract
||2010 Electronic Materials Conference
||TMS 2010 Electronic Materials Conference
||V1, Toward Conversion from Electron Pairs to Photon Pairs in Quantum Dots
||Ikuo Suemune, Yasuhiro Idutsu, Makoto Takada, Hirotaka Sasakura, Hidekazu Kumano
|On-Site Speaker (Planned)
Quantum information communication and processing are expected to form next-generation highly secure quantum-information networks (QIN). Single photons generated from semiconductor quantum dots (QDs) are expected to play as messenger qubits in QIN. Especially generation of quantum-entangled photon pairs (QEPP) is regarded to be an important key issue to further extend QIN and it has been actively studied to realize on-demand QEPP sources with QDs. Biexciton-exciton cascade photon-pair emission is the major scheme to pursue this direction. But fine-structure splitting (FSS) of exciton states is the widely recognized difficult problem at present. Also it is difficult to realize simultaneous QEPP generation based on spontaneous emissions in QDs in such a manner as the parametric down conversion of an external laser excitation source. In this paper, new possibility of generating QEPP simultaneously with spontaneous emissions in QDs is discussed. Biexciton(XX) and exciton(X) states in a QD generally have different binding energies due to the Coulomb attractive and repulsive forces among the electrons and holes. This results in different oscillator strengths of XX and X and leads to the sequential single photon spontaneous emissions. This is an intrinsic property and seems to be difficult to change. However, this situation can be changed by introducing an additional attractive force between electron pairs [1, 2]. It is well-known that electrons form Cooper pairs below critical temperature via phonon-assisted attractive force between electrons. Recently inter-band radiative recombination processes of electrons and holes in semiconductors were analyzed including the effect of the Cooper-pair formation (the proximity effect) based on second-order perturbation theory. This analysis shows that pairing of spin-singlet electrons drastically enhances the radiative recombination with a pair of holes. Such a drastic enhancement of electroluminescence (EL) has been observed from light emitting diode (LED) with niobium superconducting electrodes . This theory suggests the QEPP generation in this device. These theoretical and experimental results show the possibility of new-type of radiative recombination processes in semiconductors. However for the control of the number state of generated QEPP, inclusion of QDs in the radiative recombination process is essential . The basic requirements to achieve this scheme and the QD-related experiments demonstrating Cooper-pair-based recombination are discussed. For the confirmation of the generated QEPP with high fidelity, it is also required that the generated QEPP are efficiently extracted to the outer optical transmission systems. Some trials towards this direction is also discussed. E. Hanamura, Phys. Stat. Solid. (b) 234, 166 (2002). I. Suemune et. al., Jpn. J. Appl. Phys. 45, 9264 (2006). Y. Asano etal, Phys. Rev. Lett. 103, 187001 (2009). Y. Hayashi etal Appl. Phys. Express 1, 011701 (2008).