Synthetic diamond could be quantum computer's best friend

LONDON — Researchers at the universities of Paris and Stuttgart (Germany) with colleagues from diamond supermaterials specialist Element Six (Ascot, England) have claimed significant progress in the development of synthetic diamond suitable for the realization of quantum computers capable of operating at room temperature.

In a letter to the latest edition of Nature Materials the teams outline the results of progress of the research under the under the three-year project called "Engineered Quantum Information in Nanostructured Diamond", or EQUIND, which started in early 2007.

The project is part of the European Union's "FET Open Funding Programme" and its main aim is to establish whether specific optical features identified in diamond can be used as the basic elements for quantum computers and single-photon sources.

Aspart of the work, Element Six has been developing synthesis processes based on chemical vapour deposition (CVD) that can produce ultrapure isotopically controlled single crystal diamond that has very low concentration of paramagnetic impurities.

"For quantum applications, Element Six has been faced with the challenge of simultaneously reducing the concentration of the isotope 13C to less than 0.3 percent and reducing the concentration of other paramagnetic defects to less than 1014 cm-3" said Daniel Twitchen, senior researcher at Element Six and one of the paper's authors.

"This isotopically engineered diamond is essentially the first quantum grade purity diamond ever produced and marks a milestone for synthetic diamond produced by a CVD process," suggests Twitchen.

One of the requirements of practical quantum devices is that the individual quantum bits, or qubits, need to store information for long enough to make many computational operations, typically greater than 10 to the power of five.

A significant drawback has been that 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.

The researchers are thus focusing on 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.

The researchers say they have created single electron spins having a room temperature spin dephasing time of 1.8 ms, which they suggest is the longest ever observed in a solid state system at room temperature.

Element Six maintains 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.

The researchers say the ability of ultrapure isotopically controlled CVD diamond to detect weak magnetic fields with high local resolution might have implications in areas such as life science, metrology and quantum applications. Possible examples are diamond magnetometers used to detect magnetic fields associated with the ion flow through membrane channels in cells.

EQUIND is co-ordinated by the Ecole Normale Superieure de Cachan, near Paris and includes eight groups of researchers from academia and industry. The other partners are the Universities of Bristol and Warwick in the U.K., Stuttgart and Kiel Universities in Germany, the Academy of Science in Belarus, and the University of Melbourne in Australia. The consortium combines expertise diamond material synthesis and processing, and quantum information processing.

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