Scientists at the University of Innsbruck say they've created the first efficient and tunable interface for quantum networks.
An interface is needed to transfer information from quantum processors onto the photons that carry the information. Optical fibers will then transmit them between remote data registers, probably composed of quantum dots or ions.
The team traps a single calcium ion in a so-called Paul trap and places it between two highly reflective mirrors. They excite the ion with a laser, thereby generating a photon which is entangled with the ion and reflected back and forth between the mirrors.
Photons bounce back and forth up to 25,000 times between these mirrors, interacting with the ion, before escaping through one mirror into an optical fiber.
The entanglement between ion and photon can be custom-tuned by adjusting the frequency and amplitude of the laser.
The technique has two big advantages over previous approaches that have entangled atoms with light, says Tracy Northup of the university's Institute for Experimental Physics.
"The efficiency with which we produce entangled photons is quite high and in principle could be increased to over 99 percent," she says.
"But above all, what this setup lets us do is generate any possible entangled state."
Indeed, says the team, they've demonstrated an entangled quantum state between an atom and a photon with the highest precision ever measured.