## Abstract

A fascinating dream in quantum information science is to build quantum computers with super-performance and quantum networks with unconditional security [1]. 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 [2].

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 ~ microseconds, 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 and quantum computation.

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 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 (solid-state quantum repeaters) [5], but also for scalable quantum computing with either photons or spins as qubits. We will also discuss other applications using these gates, such as photon-number resolving detection, quantum feed-back control, loss-resistant quantum metrology, and loophole-free Bell test [6], and other devices based on optical nonlinearity at single-photon levels in these gate structures. All these schemes are feasible with current semiconductor technology [7], and we have recently seen conditional phase shifts in uncharged QD-cavity systems [8].

References

[1] H.J. Kimble, Nature (London) 453, 1023 (2008).

[2] H.-J. Briegel et al., Phys. Rev. Lett. 81, 5932 (1998).

[3] C.Y. Hu et al., Phys. Rev. B 78, 085307 (2008); ibid. 78, 125318 (2008).

[4] C.Y. Hu et al., Phys. Rev. B 80, 205326 (2009).

[5] C.Y. Hu and J.G. Rarity, Phys. Rev. B 83, 115303 (2011).

[6] N. Brunner et al., Arxiv: quant-phys 1303.6522 (2013).

[7] S. Reitzenstein et al., Appl. Phys. Lett. 90, 251109 (2007).

[8] A.B. Young et al., Phys. Rev. A 84, 011803 (2011).

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 ~ microseconds, 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 and quantum computation.

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 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 (solid-state quantum repeaters) [5], but also for scalable quantum computing with either photons or spins as qubits. We will also discuss other applications using these gates, such as photon-number resolving detection, quantum feed-back control, loss-resistant quantum metrology, and loophole-free Bell test [6], and other devices based on optical nonlinearity at single-photon levels in these gate structures. All these schemes are feasible with current semiconductor technology [7], and we have recently seen conditional phase shifts in uncharged QD-cavity systems [8].

References

[1] H.J. Kimble, Nature (London) 453, 1023 (2008).

[2] H.-J. Briegel et al., Phys. Rev. Lett. 81, 5932 (1998).

[3] C.Y. Hu et al., Phys. Rev. B 78, 085307 (2008); ibid. 78, 125318 (2008).

[4] C.Y. Hu et al., Phys. Rev. B 80, 205326 (2009).

[5] C.Y. Hu and J.G. Rarity, Phys. Rev. B 83, 115303 (2011).

[6] N. Brunner et al., Arxiv: quant-phys 1303.6522 (2013).

[7] S. Reitzenstein et al., Appl. Phys. Lett. 90, 251109 (2007).

[8] A.B. Young et al., Phys. Rev. A 84, 011803 (2011).

Original language | English |
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Title of host publication | Conference on Quantum Information and Quantum Control V, Toronto, 12-16 August, 2013 |

Publication status | Published - 16 Aug 2013 |