Point defects in super-chilled diamonds may offer stable candidates for quantum computing bits

Diamond, nature's hardest known substance, is essential for our modern mechanical world -- drills, cutters, and grinding wheels exploit the durability of diamonds to power a variety of industries. But diamonds have properties that may also make them excellent materials to enable the next generation of solid-state quantum computers and electrical and magnetic sensors.

To further explore diamonds' quantum computing potential, researchers from the University of Science and Technology of China tested the properties of a common defect found in diamond: the nitrogen-vacancy (NV) center.

Consisting of a nitrogen atom impurity paired with a 'hole' where a carbon atom is absent from the matrix structure, the NV center has the potential to store information because of the predictable way in which electrons confined in the center interact with electromagnetic waves. The research team probed the energy level properties of the trapped electrons by cooling the diamonds to an extremely chilly 5.6 degrees Kelvin and then measuring the magnetic resonance and fluorescent emission spectra. The team also measured the same spectra at gradually warmer increments, up to 295 degrees Kelvin.

The results, as reported in the AIP's journal Applied Physics Letters, show that at temperatures below 100 Kelvin the electrons' transition energies, or the energies required to get from one energy level to the next, were stable. Shifting transition energies could make quantum mechanical manipulations tricky, so cooler temperatures may aid the study and development of diamonds for quantum computation and ultra-sensitive detectors, the authors write.

The above story is reprinted (with editorial adaptations ) from materials provided by American Institute of Physics, via EurekAlert!, a service of AAAS.

Journal Reference:

X.-D. Chen, C.-H. Dong, F.-W. Sun, C.-L. Zou, J.-M. Cui, Z.-F. Han, and G.-C Guo. Temperature dependent energy level shifts of nitrogen-vacancy centers in diamond. Applied Physics Letters, 2011

New knowledge about 'flawed' diamonds could speed the development of diamond-based quantum computers

 A University at Buffalo-led research team has established the presence of a dynamic Jahn-Teller effect in defective diamonds, a finding that will help advance the development of diamond-based systems in applications such as quantum information processing.

"We normally want things to be perfect, but defects are actually very important in terms of electronic applications," said Peihong Zhang, the UB associate professor of physics who led the study. "There are many proposals for the application of defective diamonds, ranging from quantum computing to biological imaging, and our research is one step toward a better understanding of these defect systems."

The research was published online Sept. 30 in Physical Review Letters.

The findings deal with diamonds whose crystal structure contains a particular defect: a nitrogen atom that sits alongside a vacant space in an otherwise perfect lattice made only of carbon.

At the point of the imperfection -- the so-called "nitrogen-vacancy center" -- a single electron can jump between different energy states. (The electron rises to a higher, "excited" energy state when it absorbs a photon and falls back to a lower energy state when it emits a photon).

Understanding how the diamond system behaves when the electron rises to an excited state called a "3E" state is critical to the success of such proposed applications as quantum computing.

The problem is that at the nitrogen-vacancy center, the 3E state has two orbital components with exactly the same energy -- a configuration that is inherently unstable.

In response, the lattice "stabilizes" by rearranging itself. Atoms near the nitrogen-vacancy center move slightly, resulting in a new geometry that has a lower energy and is more stable.

This morphing is known as the Jahn-Teller effect, and until recently, the effect's precise parameters in defective diamonds remained unknown.

Zhang and colleagues from the Rensselaer Polytechnic Institute in Troy, N.Y., are the first to crack that mystery. Using UB's supercomputing facility, the Center for Computational Research, the team conducted calculations that reveal how, exactly, the diamond lattice distorts.

Their findings align with experimental results from other research studies, and shed light on important topics such as how long an excited electron at the nitrogen-vacancy center will stay coherently at a higher energy state.

The UB-Rensselaer study was funded by the Department of Energy.

The above story is reprinted (with editorial adaptations ) from materials provided by University at Buffalo.

Journal Reference:

Tesfaye Abtew, Y. Sun, Bi-Ching Shih, Pratibha Dev, S. Zhang, Peihong Zhang. Dynamic Jahn-Teller Effect in the NV- Center in Diamond. Physical Review Letters, 2011; 107 (14) DOI: 10.1103/PhysRevLett.107.146403

Candle flames contain millions of tiny diamonds

 The flickering flame of a candle has generated comparisons with the twinkling sparkle of diamonds for centuries, but new research has discovered the likeness owes more to science than the dreams of poets.

Professor Wuzong Zhou, Professor of Chemistry at the University of St Andrews has discovered tiny diamond particles exist in candle flames.

His research has made a scientific leap towards solving a mystery which has befuddled people for thousands of years.

Since the first candle was invented in ancient China more than 2,000 years ago, many have longed to know what hidden secrets its flames contained.

Dr Zhou’s investigation revealed around 1.5 million diamond nanoparticles are created every second in a candle flame as it burns.

The leading academic revealed he uncovered the secret ingredient after a challenge from a fellow scientist in combustion.

Dr Zhou said: “A colleague at another university said to me: “Of course no-one knows what a candle flame is actually made of.

“I told him I believed science could explain everything eventually, so I decided to find out.”

Using a new sampling technique, assisted by his student Mr Zixue Su, he invented himself, he was able to remove particles from the centre of the flame – something never successfully achieved before – and found to his surprise that a candle flame contains all four known forms of carbon.

Dr Zhou said: "This was a surprise because each form is usually created under different conditions."

At the bottom of the flame, it was already known that hydro-carbon molecules existed which were converted into carbon dioxide by the top of the flame.

But the process in between remained a mystery.

Now both diamond nanoparticles and fullerenic particles have been discovered in the centre of the flame, along with graphitic and amorphous carbon.

The discovery could lead to future research into how diamonds, a key substance in industry, could be created more cheaply, and in a more environmentally friendly way.

Dr Zhou added: “Unfortunately the diamond particles are burned away in the process, and converted into carbon dioxide, but this will change the way we view a candle flame forever.”

The famous scientist Michael Faraday in his celebrated 19th century lectures on “The Chemical History of a Candle” said in an 1860 address to the light: “You have the glittering beauty of gold and silver, and the still higher lustre of jewels, like the ruby and diamond; but none of these rival the brilliancy and beauty of flame. What diamond can shine like flame?”

Rosey Barnet, Artistic Director of one of Scotland’s biggest candle manufacturers, Shearer Candles, described the finding as "exciting".

She said: "We were thrilled to hear about the discovery that diamond particles exist in a candle flame.

"Although currently there is no way of extracting these particles, it is still an exciting find and one that could change the way people view candles. The research at St Andrews University will be of interest to the entire candle making industry. We always knew candles added sparkle to a room but now scientific research has provided us with more insight into why.”

Provided by University of St Andrews