This photo shows two black diamonds on a superconducting chip (12x4mm); the wiggly line is the microwave resonator, coupling the two diamonds. Photo: TU Wien.
This photo shows two black diamonds on a superconducting chip (12x4mm); the wiggly line is the microwave resonator, coupling the two diamonds. Photo: TU Wien.

Diamonds with minute flaws could play a crucial role in the future of quantum technology. For some time now, researchers at TU Wien in Austria have been studying the quantum properties of such diamonds, but only now have they succeeded in coupling together the specific defects in two separate diamonds. This is an important prerequisite for the development of new applications, such as highly sensitive sensors and switches for quantum computers. The researchers report their advance in a paper in Physical Review Letters.

"Unfortunately, quantum states are very fragile and decay very quickly," says Johannes Majer, head of the hybrid quantum research group at TU Wien’s Institute of Atomic and Subatomic Physics. For this reason, in-depth research is being carried out with the aim of finding quantum systems that can be used for technical applications. Although several promising candidate systems have been developed, each of which possess specific advantages, until now there has been no system that fulfills all the necessary requirements simultaneously.

"Diamonds with very specific defects are one potential candidate for making quantum computers a reality," says Majer. A pure diamond is made up solely of carbon atoms. In some diamonds, however, a nitrogen atom can replace a carbon atom at specific points, which causes a neighboring anomaly within the atomic structure of the diamond where there is no atom at all, referred to as a 'vacancy'. This defect, consisting of the nitrogen atom and the vacancy, forms a quantum system with a very long-lasting state, making diamonds with these particular flaws ideally suited for quantum experiments.

One important prerequisite for many quantum technological applications is the ability to couple such quantum systems together, which until recently had scarcely been possible for diamond systems. "The interaction between two such nitrogen-vacancy defects is extremely weak and only has a reach of around 10nm," says Majer.

With the help of a superconducting quantum chip that produces microwave radiation, this feat has now been achieved. For a number of years, the team at TU Wien has been investigating how diamonds can be manipulated with the help of microwaves. "Billions of nitrogen-vacancy defects in diamonds are coupled collectively with a microwave field," explains Majer. "In this way, the quantum state of the diamonds can be manipulated and read out."

Now, the team has succeeded in taking the next step: they were able to couple the defects in two different diamonds, one at each end of the chip, thus producing an interaction between the two diamonds. "This interaction is mediated by the microwave resonator in the chip in between; here, the resonator plays a similar role to that of a data bus in a regular computer," says Majer.

This coupling between two separate diamonds can be switched on and off selectively. "The two diamonds are rotated against each other at a certain angle," explains Thomas Astner, also at TU Wien and lead author of the paper. "Additionally, a magnetic field is applied, with the direction playing a decisive role: if both diamonds are aligned at the same angle within the magnetic field, then they can be coupled using quantum physics. With other magnetic field directions, it is possible to investigate the individual diamonds without coupling".

This story is adapted from material from TU Wien, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.