Quantum storage crystal
Credit: Australian National University
BOSTON: Using laser beams and a super cold crystal, Australian researchers stored and retrieved a quantum state of light with 69% efficiency – much higher than that of atomic vapours, used in most quantum computing research.
These findings take researchers one step closer to secure communications: in theory, a quantum computer could send a message that can only be read by one other computer, making it far more secure than today's methods.
It's the unique setup of lasers and crystals that makes the retrieval possible, the researchers said.
One-second memory
"In principle, we could store a whole image - even a holographic image. You could take photo with the lasers, and store it using this crystal," said Matt Sellars of the Australian National University in Canberra.
Sellars and his colleagues used a single pulse of photons in the form of a laser light, shining it into a crystal cooled to -270°C. The crystal is no ordinary crystal: it is coated in rare earth metal ions and surrounded by a magnetic field.
In 2005, the researchers reported that, with this set up, they could force the crystal to absorb and store photons for up to one second, which increased memory storage by more than 1,000 times.
From 17% efficiency to 69%
In this new study, the researchers report that they are able to retrieve the stored signal with 69% efficiency, by stimulating the crystal to re-emit a nearly identical pulse of photons by reversing the polarities of the magnetic field.
"So far, successful demonstrations of non-classical storage and on-demand recall have used atomic vapours and have been limited to low efficiencies, of less than 17%," the researchers wrote in their paper, published in the journal Nature.
The difference, according to Sellars, is that atomic vapors - used by most researchers in this field - have particles that are randomised and moving, whereas his team's crystal has a rigid lattice structure. That makes the crystal better at storing the photons.
