Optical tweezers for atom clouds

Physicists from the University of Otago have developed a steerable ‘optical tweezers’ unit that uses intense laser beams to precisely split minute clouds of ultracold atoms and to smash them together.

Writing in the journal Optics Letters, the researchers explained, “The tweezer system is based on high-efficiency acousto-optic deflectors and offers two-dimensional control over beam position.” They said it can be used for the transport of ultracold atoms along a narrow, static confinement channel, with the possibility for tracking the transport channel when shuttling atomic clouds along it.

Credit: Dr Niels Kjaergaard.

The team used the technology to split a single ultracold cloud of rubidium atoms sequentially into 32 daughter clouds, spreading them out over nearly half a centimetre. They steered horizontal and vertical laser beams around through their interaction with precisely controlled travelling acoustic waves. The laser beams confined and moved the atoms, and the system allowed the atom clouds to be collided.

“This sort of precise control of these atoms is like being able to pull a delicate snowflake into two clean halves with your bare hands,” said lead researcher Dr Niels Kjaergaard. “It’s quite remarkable that we are able to manipulate such minute and fragile samples while moving them such a comparatively large distance.”

The system is predicted to enhance efforts to understand the mysterious ways that atoms interact at temperatures of less than a millionth of a degree above absolute zero. According to Dr Kjaergaard, its potential applications include new tools for probing microscopic structures or for sensors that can map minute variations in magnetic fields.

“We like to refer to our set-up as the ‘Littlest Hadron Collider’,” Dr Kjaergaard said. “In some ways it’s the complete opposite of what is the world’s largest and most powerful particle collider, because instead of using extreme acceleration, we smash our atom clouds together at a pedestrian pace of up to a metre per second.”

The steerable optical tweezers unit was constructed as part of Kris Roberts’ Honour’s thesis project in Dr Kjaergaard’s research group at the Jack Dodd Centre for Quantum Technology at the Department of Physics, while the control system for the acoustic waves was built by Master’s student Thomas McKellar.

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