10 May 2011

Australian scientists make quantum breakthrough

By
Cosmos Online
In one of the most explicit demonstrations of wave-particle duality, scientists have successfully guided atoms in a laser light beam, the atoms displaying the same properties as light guided in an optical fibre.
speckle pattern

An artist’s impression of the speckle pattern created by a multimode light beam (top, red), and the image measured in this experiment created by a multimode beam of atoms (top, blue). Credit: Tim Wetherell, ANU

BRISTOL: In one of the most explicit demonstrations of wave-particle duality, scientists have successfully guided atoms in a laser light beam, the atoms displaying the same properties as light guided in an optical fibre.

The results will lead to important applications in atom interferometry, which is used to measure atomic properties and geophysical phenomena such as tides and ocean loading effects, and could potentially probe for ripples in the curvature of spacetime.

“We have imaged atomic speckle for the first time showing that guided atom-laser beams exhibit the same characteristics as guided laser light beams,” said Ken Baldwin from the ARC Centre of Excellence for Quantum-Atom Optics at the Australian National University in Canberra and co-author of the paper published in Nature Communications.

Atomic speckle and supercooled atoms

Optical speckle is a well studied property of light. In an optic fibre, speckle is created through interactions between waves of the same frequency but with different phases and amplitudes. These waves combine, or interfere, to create a wave with a randomly varying intensity.

Whilst many other wave properties of atoms have been observed before, atomic speckle had remained elusive until Baldwin and his colleagues guided atoms in a laser light beam to create the tell-tale grainy pattern of speckle.

The team cooled helium atoms to ultracold temperatures – just one millionth of a degree above absolute zero – and then dropped them into a laser light beam focused on the atom cloud.

“The atoms were guided by the laser beam onto a detector which measured the single atom arrivals to provide both the spatial profile (and thus the speckle) as well as atom bunching,” explained Baldwin. This crucially showed that atom bunching is a characteristic of the speckle.

Atom interferometry

The performance of an atom interferometer fundamentally depends on a property called coherence: a measure of interference.

“We have shown that multimode guiding is associated with atom bunching, whereas single mode guiding does not show atom bunching, indicating that the single guided mode is coherent,” said Baldwin. This means that atom bunching could be used as a diagnostic tool to measure the coherence properties of the guiding process for atom interferometers.

Atom interferometry is at an early stage of development. Current atom interferometers rely on freely falling atoms but future systems are likely to be based on guided atoms.

As such, these results “add significant new knowledge and might guide the design of the parameter space for future experiments in atom interferometry”, said Kai Bongs from the Midlands Ultracold Atom Research Centre in Birmingham, who was not involved in the study. “It will help in the design of future guides matter wave system, that is, it will have impact on atom ‘fibre’ optics.”

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