Delft University of Technology tests quantum mechanics with diamond

Element Six—the world leader in synthetic diamond supermaterials and member of The De Beers Group of Companies—announced today that research partners at Delft University of Technology1, using specially engineered Element Six diamonds, have successfully completed a landmark experiment testing quantum mechanics.

The collaboration, led by professor Ronald Hanson of Delft University of Technology, used two synthetic diamonds of millimeter-size that were grown by Element Six using chemical vapor deposition (CVD).  These diamonds contained a particular defect that can be manipulated using light and microwaves. This defect consists of a single nitrogen atom adjacent to a missing carbon atom, known as a nitrogen vacancy (NV) defect. The light emitted from the NV defect allows the quantum properties to be “read-out” using an optical microscope. By forming small crystallographically aligned lenses around the NV defect and carefully tuning the optical emission through electric fields, the Delft team was able to make the two NV defects emit indistinguishable particles of light (photons). These photons contained the quantum information from the NV defects and via further manipulation, the team was able to quantum mechanically entangle the two defects over a distance of 1.3 km.

This entanglement process, what Albert Einstein called “spooky action at a distance,” is a process where the two NV defects become strongly connected such that they are always correlated irrespective of the distance between them. To date, many experiments probing this quantum principle have shown it to be true, however always with the caveat of loopholes, meaning there were other possible interpretations consistent with the data. This work, for the first time, demonstrates the principle and closes both the locality and detection loopholes.

“The field of synthetic diamond science is moving very quickly, requiring us to develop CVD techniques that produce exceptionally pure synthetic diamond material with nano-engineering control,” said Bruce Bolliger, head of sales and marketing at Element Six Technologies. “We are thrilled our diamond material was leveraged in such a groundbreaking experiment, and look forward to future developments in this field.”

The findings, published in last month’s issue of Nature2, are a major leap forward for quantum science and demonstrate Element Six’s ability to engineer a single atom-like defect in the diamond lattice at the parts per trillion level. It is the first time that qubits in two separated diamonds have been entangled over such a large distance. In the Delft experiment, two diamonds were placed in labs on opposite sides of the university campus, with each containing an electron trapped in the diamond’s nitrogen vacancy. The team then hit the diamonds with microwave pulses and laser light, causing each electron to emit a photon entangled with the electron’s magnetic spin. The photons then traveled to a third location in between the two labs where photo detection heralded generation of entanglement. In such cases, the distant electrons’ spins were independently measured in a randomly chosen direction. After 245 measurements, the labs detected more highly correlated spins than local realism would allow – closing the loopholes.

“Element Six’s synthetic diamond material has been at the heart of these important quantum mechanics developments, which promise to revolutionize information technologies,” said Hanson. “Building on five years of collaboration, our research partnership has been critical in overcoming one of the greatest challenges of our time—finding and controlling a physical system suitable for fulfilling the promises of quantum entanglement while at the same time testing the very nature of our understanding of quantum mechanics. This is an important step towards creating a quantum network to process information, and hence towards a future quantum computer.”