2 research outputs found
Toward Optimized Surface δ‑Profiles of Nitrogen-Vacancy Centers Activated by Helium Irradiation in Diamond
The negatively charged nitrogen-vacancy
(NV) center in diamond has been shown recently as an excellent sensor
for external spins. Nevertheless, their optimum engineering in the
near-surface region still requires quantitative knowledge in regard
to their activation by vacancy capture during thermal annealing. To
this aim, we report on the depth profiles of near-surface helium-induced
NV centers (and related helium defects) by step-etching with nanometer
resolution. This provides insights into the efficiency of vacancy
diffusion and recombination paths concurrent to the formation of NV
centers. It was found that the range of efficient formation of NV
centers is limited only to approximately 10 to 15 nm (radius) around
the initial ion track of irradiating helium atoms. Using this information
we demonstrate the fabrication of nanometric-thin (δ) profiles
of NV centers for sensing external spins at the diamond surface based
on a three-step approach, which comprises (i) nitrogen-doped epitaxial
CVD diamond overgrowth, (ii) activation of NV centers by low-energy
helium irradiation and thermal annealing, and (iii) controlled layer
thinning by low-damage plasma etching. Spin coherence times (Hahn
echo) ranging up to 50 μs are demonstrated at depths of less
than 5 nm in material with 1.1% of <sup>13</sup>C (depth estimated
by spin relaxation (T<sub>1</sub>) measurements). At the end, the
limits of the helium irradiation technique at high ion fluences are
also experimentally investigated
Protecting a Diamond Quantum Memory by Charge State Control
In
recent years, solid-state spin systems have emerged as promising
candidates for quantum information processing. Prominent examples
are the nitrogen-vacancy (NV) center in diamond, phosphorus dopants
in silicon (Si:P), rare-earth ions in solids, and V<sub>Si</sub>-centers
in silicon-carbide. The Si:P system has demonstrated that its nuclear
spins can yield exceedingly long spin coherence times by eliminating
the electron spin of the dopant. For NV centers, however, a proper
charge state for storage of nuclear spin qubit coherence has not been
identified yet. Here, we identify and characterize the positively
charged NV center as an electron-spin-less and optically inactive
state by utilizing the nuclear spin qubit as a probe. We control the
electronic charge and spin utilizing nanometer scale gate electrodes.
We achieve a lengthening of the nuclear spin coherence times by a
factor of 4. Surprisingly, the new charge state allows switching of
the optical response of single nodes facilitating full individual
addressability