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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

ERC

Preferential orientation of NVs in diamond

Perfect alignment and preferential orientation of nitrogen vacancy centers during CVD growth of diamond on (111) surfaces

Synthetic diamond production is key to the development of quantum metrology and quantum information applications of diamond.
The major quantum sensor and qubit candidate in diamond is the nitrogen vacancy (NV) color center. This lattice defect comes in four different crystallographic orientations leading to an intrinsic inhomogeneity among NV centers that is undesirable in some applications. In this work, we report a microwave plasma-assisted chemical vapor decomposition (MPCVD) diamond growth technique on (111)-oriented substrates that yields perfect alignment (94 %) of as-grown NV centers along a single crystallographic direction. In addition, clear evidence is found that the majority (74 %) of the aligned NV centers were formed by the nitrogen being first included in the (111) growth surface and then followed by the formation of a neighboring vacancy on top.

The achieved homogeneity of the grown NV centers will tremendously benefit quantum information and metrology applications using identical qubits. In a NV spin ensemble up to 75 % of all spins might be unusable and, worse still, the unusable spins may deteriorate the device performance.

Optically detected magnetic resonance (ODMR) techniques are applied to the NV centers to verify their alignment. Due to refined insight into the NV centers properties the orientation of the N-V pair can now also be determined using the combined application of electric and magnetic fields.
More specifically, ODMR was combined with an axially aligned magnetic field to verify the alignment of the NV centers and ODMR was combined with both transverse magnetic and electric fields to determine the orientations of the NV centers. Such a measurement images the C3v symmetry of the NV center. As the diamond structure was independently determined via x-ray crystallography, the orientation of the NV center could be via the geometry of the diamond lattice.


Fig. 1: The diamond was grown in several steps, as the diamond had to be etched during the growth process (b.) to enable a growth in the <111> direction. During the normal growth process, (a.) and (c.), an C12 isotopic enriched methane flow was used. (d.) shows a Normarski-mode optical microscope image of the fully grown diamond.


Fig. 2: For NVs aligned with the <111> crystal axis, two different orientations are possible, with the nitrogen atom up (red) and down (blue). These two different orientations lead to two 'three-leaves' that are shifted relatively to each other in the spin level shift while rotating a vertical magnetic and electric field.