The ultimate goal of quantum information science is to build quantum networks for distributed quantum computing or for the secure sharing of information between spatially remote parties . Quantum networks utilize static (matter) quantum bits (qubits) to store and process quantum information at local nodes, and photons as flying qubits for long-distance quantum state transmission between different nodes. To realize a quantum network, it is crucial to achieve light-matter entanglement and reversible quantum-state transfer between light and matter, i.e., the light-matter quantum interface, and the quantum repeater for large-scale quantum communications . Recent experiments have shown that both electrons and holes confined in semiconductor quantum dots (QDs) have long spin relaxation time (T1e, T1h ~ ms) and long spin coherence time (T2e ~ s, T2h > 100 ns). Moreover, fast spin cooling and ultra-fast spin manipulation as well as spin echoes to preserve the spin coherence have also been demonstrated. Undoubtedly these rapid progresses imply that the QD spin is a good candidate for matter qubit in quantum information processing. Furthermore, QD-based single photon sources have been also developed. Therefore, semiconductor QDs offer a good platform for solid-state quantum networking. Here we present two types of conditional quantum gates, i.e., the photon-spin entangling gates [3-4] using a single QD spin in a single-sided or double-sided optical microcavity. Both gates are universal and deterministic (if they are optimized). The spin-selective coherent photon-spin interaction enhanced by the cavity QED lead to giant circular birefringence, which allows us to build these gates. We will show some of the key applications [3-5], including: (i) single-shot quantum non-demolition measurement of spin; (ii) single-photon based spin manipulations and spin echoes to preserve the spin coherence; (iii) photon-spin, spin-spin and photon-photon entanglement generation with high fidelity and high efficiency; (iv) deterministic photon-spin interface and perfect spin memory; (v) complete and loss-resistant Bell-state analyzer, which could increase the distance of state-of-the-art quantum communications by one order of magnitude (from current 100 km to over 1000 km) ; (vi) the full quantum repeater combining quantum memory, entanglement swapping and purifications for arbitrary long distance communications ; (vii) spin-controlled single photon sources. All these schemes are feasible with current semiconductor technology , and we have recently seen conditional phase shifts in uncharged QD-cavity systems . The versatile spin-cavity systems can be applied in all aspects of quantum information science and technology, not only for large-scale quantum communication networks, but also for scalable quantum computing with either photons or spins as qubits. References  H.J. Kimble, Nature (London) 453, 1023 (2008).  H.-J. Briegel et al., Phys. Rev. Lett. 81, 5932 (1998).  C.Y. Hu et al., Phys. Rev. B 78, 085307 (2008); ibid. 78, 125318 (2008).  C.Y. Hu et al., Phys. Rev. B 80, 205326 (2009).  C.Y. Hu and J.G. Rarity, ArXiv: quant-ph 1005.5545 (2010).  S. Reitzenstein et al., Appl. Phys. Lett. 90, 251109 (2007).  A.B. Young et al., ArXiv: quant-ph 1011.0384 (2010).
|Translated title of the contribution||Quantum-dot spin in an optical microcavity for quantum information technology|
|Title of host publication||11th International Conference on Physics of Light-Matter Coupling in Nanostructures (PLMCN 11), April 4-8, Berlin|
|Publication status||Published - 2011|