A team of physicists at the Yokohama National University, Japan, has successfully demonstrated quantum teleportation — the remote exchange of quantum states — in a diamond.
“Quantum teleportation is a key principle for quantum information technology. It permits the transfer of quantum information into an otherwise inaccessible space,” Professor Hideo Kosaka, senior author of the study.
“It also permits the transfer of information into a quantum memory without revealing or destroying the stored quantum information.”
The inaccessible space, in this case, consisted of carbon atoms in diamond. Made of linked, yet individually contained, carbon atoms, a diamond holds the perfect ingredients for quantum teleportation.
A carbon atom holds six protons and six neutrons in its nucleus, surrounded by six spinning electrons. As the atoms bond into a diamond, they form a notoriously strong lattice.
Diamonds have complex defects, though, when a nitrogen atom exists in one of two adjacent vacancies where carbon atoms should be. This defect is called a nitrogen-vacancy center.
Surrounded by carbon atoms, the nucleus structure of the nitrogen atom creates what the physicists call a nanomagnet.
To manipulate an electron and a carbon isotope in the vacancy, Professor Kosaka and colleagues attached a wire about a quarter the width of a human hair to the surface of a diamond.
The researchers applied a microwave and a radio wave to the wire to build an oscillating magnetic field around the diamond.
They shaped the microwave to create the optimal, controlled conditions for the transfer of quantum information within the diamond.
They then used the nitrogen nanomagnet to anchor an electron.
Using the microwave and radio waves, they forced the electron spin to entangle with a carbon nuclear spin — the angular momentum of the electron and the nucleus of a carbon atom.
The electron spin breaks down under a magnetic field created by the nanomagnet, allowing it to become susceptible to entanglement.
Once the two pieces are entangled, meaning their physical characteristics are so intertwined they cannot be described individually, a photon which holds quantum information is applied and the electron absorbs the photon.
The absorption allows the polarization state of the photon to be transferred into the carbon, which is mediated by the entangled electron, demonstrating a teleportation of information at the quantum level.
“The success of the photon storage in the other node establishes the entanglement between two adjacent nodes. Called quantum repeaters, the process can take individual chunks of information from node to node, across the quantum field,” Professor Kosaka said.
“Our ultimate goal is to realize scalable quantum repeaters for long-haul quantum communications and distributed quantum computers for large-scale quantum computation and metrology.”
The results appear in the journal Communications Physics.
Kazuya Tsurumoto et al. 2019. Quantum teleportation-based state transfer of photon polarization into a carbon spin in diamond. Communications Physics 2, article number: 74; doi: 10.1038/s42005-019-0158-0