Dephasing Due To Nuclear Spins in Large-Amplitude Edsr
Update: 2017-03-02 15:18:10      Author: yangjuan@csrc.ac.cn

Electric manipulation of spins in quantum dots can be achieved using Electric Dipole Spin Resonance (EDSR). The local control and the fast timescales allowed by EDSR might prove decisive advantages with respect to alternative approaches for single-spin manipulation. Therefore, this technique may become a cornerstone in complex architectures of many quantum dots, which are a promising platform to implement quantum information processing [1].

To further improve the performance of EDSR, it is necessary to characterize dominant dephasing mechanisms. An especially interesting limit is the strong electric drive regime, which was recently achieved experimentally [2, 3] and allows to further reduce the spin manipulation times. However, the main sources of noise are still poorly understood in this regime. A recent investigation [4], involving Stefano Chesi and Li-Ping Yang of CSRC and Daniel Loss from Basel University, has developed a comprehensive theory of dephasing caused by nuclear spins in EDSR, revealing new surprising features which appear in the strong-drive regime.

Nuclear spins are known for about 10 years as a dominant source of dephasing in quantum dots, but the general understanding has been that nuclear noise perpendicular to the direction of the external magnetic field has a negligible effect. On the other hand, the results of Ref. [4] show that the transverse nuclear noise becomes increasingly more effective at large drive strength, and eventually dominates over the longitudinal nuclear fluctuations. The presence of strong transverse noise causes qualitative and quantitative changes in the observed behavior of dephasing, which are in agreement with experiments. In fact, the theory developed in [4] has allowed to explain the decay of Rabi oscillation observed in recent EDSR experiments performed in Delft [2] and the University of Tokyo [3], which reached for the first time the strong–drive regime.

Despite the additional noise from transverse nuclear fields, EDSR remains a promising technique. As shown in [4], increasing the drive strength is always beneficial for accurate spin manipulation because the shorter operation time more than compensates the reduced coherence time.

 

References:

[1]     D. Loss and D. P. DiVincenzo, Phys. Rev. A 57, 120 (1998).

[2]     J.W. G. van den Berg, et al., Phys. Rev. Lett. 110, 066806 (2013).

[3]     J. Yoneda, et al., Phys. Rev. Lett. 113, 267601 (2014).

[4]     S. Chesi, L.-P. Yang, and D. Loss, “Dephasing due to Nuclear Spins in Large-Amplitude Electric Dipole Spin Resonance”, Phys. Rev. Lett. 116, 066806 (2016), (pub. 12 February 2016). DOI: 10.1103/PhysRevLett.116.066806

 

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Fig. 1: Comparisons of EDSR theory [4] and experiments [2, 3]. (a): Fit of the Rabi oscillations from [2]. (b): Extracted ratio of the amplitude of the EDSR-induced motion dR and the quantum dot size dx. Bottom panels: comparison of the theoretical [4] and experimental [3] “Chevron” pattern of the Rabi oscillations, obtained at large drive strength.


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