Three Times Higher Carbon 12 Purity for Synthetic Diamond Enables Better Quantum Computing

Element Six is a global leader (Europe based) and innovator in supermaterials with a history spanning more than 50 years.

Element Six has created synthetic diamond with less carbon 13 isotope and more pure carbon 12, which enables longer quantum coherence times to be maintained longer. Note: Normally 1.07% is carbon 13 isotope. They have reduced this ratio by over three times.

Element Six has been faced with the challenge of simultaneously reducing the concentration of the isotope 13C to less than 0.3% and reducing the concentration of other paramagnetic defects to less than 10^14 cm-3.

The full 5 page paper is available.

With the current limit in dephasing times (1.8 ms), two nitrogen-vacancy electron spins, at a distance of 100nm, will be coherently coupled. This distance is sufficient for the two centres to be addressed and read out separately by modern methods of nonlinear optical microscopy and also manufacturable with current implantation techniques that allow some 10nm precision.

As the distance at which coherent coupling prevails scales as cube root of NC, a further reduction of the 13C concentration by one order of magnitude would enable an increase of the mutual separation by roughly a factor of 2.

Note that the ultimate limit for the coherence time of a spin-free diamond host is given by spin-lattice relaxation, which is expected to occur in a seconds timescale. In this case, micrometre-scale-separated electron spins would show coherent coupling, an almost macroscopic scale quantum array.

Isotopic enrichment was accomplished by using purifiers to reduce non-intentional dopants and isotopically enriched methane at 99.7% in a hydrogen environment (95% by composition). These conditions led to samples in which the paramagnetic impurity concentration (including nitrogen, hydrogen and silicon defects) was minimized.

Longer Quantum Coherence Any unintentional defects with paramagnetic spin in the diamond can result in the qubits rapidly losing their quantum information, severely limiting the number of possible computations. So researchers are putting a great deal of effort into increasing “coherence time” which is one of the many challenges to building practical computers. This requires developing quantum purity diamond with a very low defect spin concentration. In this letter to Nature Materials, the EQUIND consortium report, single electron spins having a room temperature spin dephasing time of 1.8 ms, the longest ever observed in a solid state system at room temperature.

Better Magnetic Imaging Application

Diamond with these properties is also applicable to research into a new type of nanometre-scale magnetic sensors that could be used in biological imaging. In their letter, the researchers note, “The ability of ultrapure isotopically controlled CVD diamond to detect weak magnetic fields with high local resolution might have implications in a wide range of fields such as: life science, metrology and quantum applications. A possible example are diamond magnetometers used to detect magnetic fields associated with the ion flow through membrane channels in cells.”

Nature Materials : Ultralong spin coherence time in isotopically engineered diamond Published online: 6 April 2009 | doi:10.1038/nmat2420

As quantum mechanics ventures into the world of applications and engineering, materials science faces the necessity to design matter to quantum grade purity. For such materials, quantum effects define their physical behaviour and open completely new (quantum) perspectives for applications. Carbon-based materials are particularly good examples, highlighted by the fascinating quantum properties of, for example, nanotubes or graphene. Here, we demonstrate the synthesis and application of ultrapure isotopically controlled single-crystal chemical vapour deposition (CVD) diamond with a remarkably low concentration of paramagnetic impurities. The content of nuclear spins associated with the 13C isotope was depleted to 0.3% and the concentration of other paramagnetic defects was measured to be