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Accueil du site > Vie du laboratoire > Congrès / Colloques / Conférences > Optical Properties of Individual Nanowires and Quantum Dots in High Magnetic Field, Septembre 2014 > Programme du workshop > Abstract : Optically detected nuclear magnetic resonance in self-assembled quantum dots

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Abstract : Optically detected nuclear magnetic resonance in self-assembled quantum dots

 

Evgeny A. Chekhovich

Department of Physics and Astronomy, University of Sheffield, Sheffield, S3 7RH

 

Quantum dots in III-V semiconductors have various favourable properties for applications in quantum information technologies, including strong coupling with light offering excellent optical interfacing, ultrafast coherent manipulation and advanced manufacturing technologies. However, all group III and V atoms have nonzero nuclear spins. Thus instead of a two-level qubit system, the spin of a single electron in a quantum dot is described by the so called ’’central spin’’ problem [1, 2], where the electron (central) spin is strongly coupled to an ensemble of few thousand nuclear spins. This electron-nuclear (hyperfine) interaction causes electron spin decoherence and presents a serious challenge on the way towards practical applications of quantum dots in quantum computing.

In this talk, I will show how nuclear magnetic resonance (NMR) techniques can be used to study and manipulate the nuclear spin system of individual quantum dots [3, 4]. In particular, I will focus on self-assembled quantum dots, where strain-induced quadrupolar effects have a dramatic impact on nuclear spin physics. Two aspects of NMR techniques will be discussed : Firstly, NMR can be used for non-invasive structural analysis, allowing chemical composition and strain distribution to be probed within a volume of an individual quantum dot [3]. Secondly, pulsed NMR can be employed to study coherent dynamics of the nuclear spin bath. I will present our most recent results on pulsed NMR measurements of individual self-assembled dots [5], and demonstrate that strain-induced quadrupolar effects lead to enhanced nuclear spin coherence and strong suppression of nuclear spin bath fluctuations. This implies enhanced electron spin coherence, making strained III-V semiconductor nanostructures particularly attractive for applications in quantum information processing.

As it is common in magnetic resonance, the higher the available magnetic field – the better. Throughout this talk I will show that the same logic applies to NMR on quantum dots. I will demonstrate how high magnetic fields can be used to suppress second-order quadrupolar interactions thus increasing spectral resolution. Furthermore, high magnetic fields can be used to control the nuclear-nuclear interactions and achieve better understanding of nuclear spin bath dynamics.

[1] B. Urbaszek, et al., "Nuclear spin physics in quantum dots : An optical investigation" (Review), Rev. Mod. Phys. 85, 79 (2013)
[2] E. A. Chekhovich, et al., "Nuclear spin effects in semiconductor quantum dots" (Review), Nature Materials 12, 494 (2013)
[3] E. A. Chekhovich, et al., ”Structural analysis of strained quantum dots using nuclear magnetic resonance”. Nature Nanotechnology 7, 646 (2012).
[4] E. A. Chekhovich, et al., ”Element-sensitive measurement of the hole–nuclear spin interaction in quantum dots”. Nature Physics 9, 74 (2013).
[5] E. A. Chekhovich et al., ”Quadrupolar induced suppression of nuclear spin bath fluctuations in self-assembled quantum dots”. Preprint arXiv:1403.1510 (2014).