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Quantum information exchange between photons and electrons in solids

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Spin is a fundamental property of electrons and plays an important role in information storage. For spin-based quantum information technology, write (preparation) and read-out (measurement) processes of the electron spin state should be coherent. However, both the traditional write and read-out processes were projections to up/down spin states, which do not preserve spin coherence. We have recently demonstrated that we can transfer the polarization coherence of light to the spin coherence of electrons in a semiconductor quantum nanostructure [1], and we can also read out the prepared coherence of the electron spin optically by the developed tomographic Kerr rotation (TKR) method [2]. In these demonstrations, it was important to set the g-factor of an electron to be nearly zero. We have also demonstrated that the spin coherence of a single electron trapped in a gate-defined quantum dot, where the g-factor of electrons is tuned to nearly zero, can be electrically manipulated with a microwave applied to the gate utilizing electric-dipole spin resonance (EDSR) [3]. The fabricated quantum dot with a point contact as a charge sensor evidenced that a single electron is actually created by the absorbed photon in the dot [4]. We have also theoretically shown that two-electron coherence can be manipulated and measured via spin-flip tunneling with the help of the spin-orbit interaction [5]. Furthermore, we have shown that the full Bell-state measurement needed for the quantum repeater can even be achieved with help of g-factor engineering and g-factor switching [6].

[1] H. Kosaka et al. Phys. Rev. Lett. 100, 096602 (2008). [2] H. Kosaka et al. Nature 457, 702 (2009). [3] T. Kutsuwa et al., Physica E, 42, 821 (2010). [4] M. Kuwahara et al., App. Phys. Lett., to be published. [5] N. Yokoshi et al., Phys. Rev. Lett. 103, 046806 (2009). [6] N. Yokoshi et al., Phys. Rev. B Rapid Communications, to be published.

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