Sending quantum messages over long distances will be challenging. The signal will have to be amplified every few hundred kilometres, but conventional optical amplification would destroy the quantum message.
In a quantum information system, if you measure the light, you will destroy the information encoded on it. You need to store the light itself.
“We have to catch and store the light, but we’re not allowed to look at it to see what information it contains. If the system is working, the light will be exactly the same when we let it out again. We do this by absorbing the light into a cloud of atoms,” says Dr Ben Buchler.
He and his team at the Australian National University are tackling this challenge by creating a system called Gradient Echo Memory, which can successfully store and retrieve quantum information.
To do this, Ben’s team tuned the light to the same frequency as rubidium atoms. When the light interacted with the atoms, it created a long-lasting electron pattern in the atoms, which absorbed the light and its information. To retrieve the information, a laser converted it back into a travelling pulse of light.
“At the moment, our system is the most efficient of all the research efforts to store and retrieve quantum information, with 87 per cent of the light being recalled,” Ben says.
Banner image: Ben (front) and his colleague put the quantum memory experiment through its paces.