Remember that scene in "The Force Awakens" where the dark side warrior Kylo Ren stops a laser blast in mid-air? In a Canberra laboratory, physicists have managed a feat almost as magical: they froze the movement of light in a cloud of ultracold atoms. This discovery could help bring optical quantum computers from the realms of sci-fi to reality.
The experiment, published in a paper this week, was inspired by a computer stimulation run by lead researcher Jesse Everett from the Australian National University. The researchers used a vaporized cloud of ultracold rubidium atoms to create a light trap, into which they shone infrared lasers. The light trap constantly emitted and re-captured the light.
"It's clear that the light is trapped – there are photons circulating around the atoms," Everett says. "The atoms absorbed some of the trapped light, but a substantial proportion of the photons were frozen inside the atomic cloud."
This is not the first time physicists have stopped light, but it is the first experiment that was designed to prove beyond doubt that the trapped light was rendered stationary. The atomic cloud was imaged from the side as one method of confirming the theory.
Knowing that scientists can now stop the movement of light is an exciting development because it could allow the interactions of light and atoms to be manipulated with the extreme precision needed to develop quantum logic gates – the building blocks of the quantum computer model.
Conventional electronic computers work with units of data called bits. Bits are dependent on whether power is moving through a wire or not. They're either on or off, which we assign as a state of 1 or 0.
In conventional computing, logic gates are simple electronic circuits that can compare the on/off states of one or two incoming currents and then send on a new outgoing current according to the combined state of these incoming currents. The gates use combinational logic to serve as the building blocks of the most complex digital circuits.
Because of the complexity of the way light works, quantum bits, called qubits, can assume more complex states than electronic bits. If we can get quantum computing right, we should be able to assign each qubit a state of 0, 1, or both states at once. This ability to assume multiple states is the reason quantum computing is such an inspiring idea – it should be able to perform many different operations at once, at incredible speeds.
At this stage, we're still looking for a reliable, scalable quantum logic gate that can communicate with two qubits at once. That's why the race is on to find new ways to get photons (the particles that make up light) to interact with each other.
Co-researcher Geoff Campbell from ANU explained that while photons generally pass by each other at the speed of light without any interactions, atoms interact with each other more readily.
"Corralling a crowd of photons in a cloud of ultra-cold atoms creates more opportunities for them to interact," Campbell says.
Optical quantum computers could connect easily with fibre optics and reolutionize the way we manage big data in fields such as medicine, defence, telecommunications and financial services.
"Optical quantum computing is still a long way off, but our successful experiment to stop light gets us further along the road," says Everett.
The study appears this week in Nature Physics. The researchers talk more about their work and its possibilities in the video below.
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