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Semiconductor Quantum Dot Spin Based Quantum Computing Using Optically Excited Microcavity Exciton-Polaritons.

January 27, 2014 - 3:00pm
Speaker: 
Shruti Puri
Institution: 
Stanford

Quantum dots with optically controlled spins known as QuDOS are promising candidates for large scale quantum computation. The complete ultrafast optical control of an electron spin in a charged quantum dot (QD) has been demonstrated [1]. However, a two-qubit operation, which requires interaction between two neighboring spins is yet to be implemented. Recently, a two-qubit gate based on dispersive interaction in cavity QED system has been proposed [2]. The drawback of this scheme is the high cooperativity factor required to reach error rates below the threshold for fault-tolerant operation. Another challenge is the fast, high fidelity, single-shot measurement of the qubit state. The current readout schemes are either slow (such as the one based on QD molecules [3]) or low fidelity (such as the one based on fluorescence from a pseudo-cycling transition in a single QD [4]).

In this talk, I will discuss our recent proposal for implementing single-qubit, two-qubit gate [5] and quantum non-demolition (QND) measurement [6] of the electron spins in site controlled quantum dots, using their Coulomb exchange interaction with optically excited exciton-polaritons in a nearby quantum well (QW) (see Fig. 1). The QDs are grown a few monolayers above the QW, so that the QD electron wavefunction has a non-negligible overlap with the QW polariton wavefuction. The resulting spin-dependent Coulomb exchange interaction causes a shift in the resonance energies of QD electron and QW polariton. I will explain how these spin-dependent energy shifts can be exploited for fast and high fidelity qubit operations.

References:

[1] De Greve K, et al. 2013 Reports on Progress in Physics 76 (9), 092501.

[2] Ladd TD and Yamamoto Y. 2011 Phys. Rev. B 84, 235307.

[3] Vamivakas A N, et al. 2010 Nature 467 297.

[4] Delteil A, et al. 2013 arXiv:1310.8529.

[5] Puri S and Yamamoto Y. 2012 Phys. Rev. B 85, 241403(R).

[6] Puri S, McMahon PL, and Yamamoto Y. 2013 arXiv:1310.4873.

 

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