Synopsis: Towards nuclear spin control

Optical tuning of resonant NMR frequencies of nuclear spins in a single quantum dot achieves spatial resolution below the size of the dot.

Nuclear spins in semiconductor quantum dots have very long relaxation and coherence times, both centrally important properties for the construction of future spintronic devices and quantum computers. Direct control of nuclear spins at the nanoscale by resonant techniques such as NMR is another highly desirable milestone for the realization of these devices. Cutting-edge optically detected NMR (ODNMR) techniques are currently able to control as few as ${10}^{4}$ nuclei within a length scale of $100\phantom{\rule{0.333em}{0ex}}\text{nm}$.

Now, in an article published in Physical Review B, Maxim Makhonin and collaborators from the University of Sheffield in the UK demonstrate a new ODNMR technique achieving two orders of magnitude improvement in resolution. Their idea is to use the strong localization of an electron confined in a semiconductor quantum dot to generate an effective magnetic field (Knight field) with strong gradients, which arise from the shape of the electron wave function. The proposed method exploits the inhomogeneities in the corresponding Knight shifts to selectively access, by appropriate resonant frequencies, small groups of nuclear spins located in different regions within the quantum dot. – Athanasios Chantis

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