By Allison Kubo Hutchison

In late 1940, Debeers Diamond began using the slogan “Diamonds are forever” to promote diamond engagement rings. What they didn’t know is that this could be true regarding quantum mechanics. Diamonds are made of pure carbon, with the atoms arranged in a tetrahedral shape in a strong, rigid crystal structure. They are the hardest known material, which means that they have a hardness of 70-150 GPa in the Vickers hardness test. This hardness is inherited from its strong crystal structure and is exactly what diamond is forever.

Green indicates carbon atoms within a diamond crystal structure. With nitrogen, a void can form, basically an empty hole in the crystal. NIST, Nitrogen vacancy center, marked as public domain.

All materials have specific quantum states that are extremely fragile. You need to be isolated from anything to be measured, but even measurement can change it. However, due to their structure, diamonds can maintain quantum states long enough for measurements. Which is basically forever. In particular, defects on the atomic scale of the diamond, a nitrogen atom in which a carbon atom should be located, can be measured and used for quantum mechanical applications. A specific defect in the crystal structure that would be undesirable in a wedding ring, but is ideal for physical applications, is the nitrogen vacancy (NV). The spin quantum numbers of the NV defect can be measured by directing certain wavelengths of green light onto the defect. The amount of light emitted by the defect depends on the ground state spin. When green light is applied, the electrons also go through the spin state and finally reach ms = 0 and can then be manipulated in further experiments. This is a major breakthrough as the behavior is known and can be observed at room temperature, a luxury in many areas of quantum mechanics. Where most materials have volatile quantum states, diamonds hold theirs.

One of the main goals of this work is to use diamonds, especially the NV site, as the basis for the quantum computer. The defects are incredibly small, the size of two atoms, but are also incredibly sensitive to magnetic fields. If you change the magnetic field by up to a nanotesla, the luminosity of the NV site changes, indicating a change in spin. Very small sensors could be made in this way. Imagine a quantum computer with diamond circuits in which every defect in the nanometer range stores a “qubit”, a quantum computer bit. However, to take advantage of this we need to create incredibly precise defects in synthetic diamonds. Diamonds that were once valued for their beauty and clarity are now valued for their flaws.



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