Diamond Materials

Diamond Materials for Quantum Application

23. September 2014: The DFG research group FOR 1493 “Diamond Materials and Quantum Applications” goes into its second funding period. FOR1493 is a national research consortium funded by the Deutsche Forsch-ungsgemeinschaft.

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ERC Advanced Grant


Protecting a diamond quantum memory by charge state control

Switching on and off the coupling of proximal nuclear spins to the outside world

In recent years, solid-state spin systems have emerged as promising candidates for quantum information processing and sensing applications. Prominent examples are the nitrogen-vacancy (NV) center in diamond, phosphorous dopants in silicon (Si:P), rare-earth ions in solids and V Si -centers in silicon-carbide. Typically, nuclear spins serve as memories whereas the electron spins of these candidate systems grant access to the memories in the first place. For example, the NV center electron spin state determines the photoluminescence response. In all these systems, however, the electron spin is not only a gift but also a burden. Its fast relaxation decreases the quantum memory’s lifetime. The Si:P system has demonstrated that its nuclear spins can yield exceedingly long quantum memory lifetimes by eliminating the electron spin of the dopant. For NV centers, however, a proper charge state for storage of quantum information has not been identified yet. In our recent publication, we have identified and characterized the positively-charged NV center as an electron-spin-less and optically inactive state by utilizing the nuclear spin qubit as a probe. We have controlled the electronic charge and spin utilizing nanometer scale gate electrodes. As a result, we have improved the quantum memory’s lifetime by a factor of four. Surprisingly, the new charge state allows switching the optical response of single NV spin systems facilitating full individual addressability even in dense arrays with mutual distances below the optical diffraction limit. Our results, open up new and promising possibilities for scaling up magnetic-dipole-coupled, NV center quantum registers in diamond. Furthermore, improved quantum storage times and optical switching improve applications in quantum communication, as for example in quantum repeaters.

Figure: Two photoluminescence (PL) microscopy images of the same NV center in different charge states (NV -, NV +). The polarity (+,-) of adjacent electrodes allows setting the charge state. While NV - exhibits an electron and a nuclear spin (blue and purple arrow), NV +only possesses a nuclear spin, which is therefore very isolated from many noise sources.

M. Pfender, N. Aslam, P. Simon, D. Antonov, G. Thiering, S. Burk, F. Fávaro de Oliveira, A. Denisenko, H. Fedder, J. Meijer, J. A. Garrido, A. Gali, T. Teraji, J. Isoya, M. W. Doherty, A. Alkauskas, A. Gallo, A. Grüneis, P. Neumann, and J. Wrachtrup, Protecting a diamond quantum memory by charge state control, Nano Lett. (2017), doi: 10.1021/acs.nanolett.7b01796