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Physicists have devised a way to combine an atomic magnetometer with a gyroscope, using a pulsed laser system and a simple mixture of gases.
The new technique will not only be a radical improvement for precision measurements of rotation, but has the potential to be a powerful tool in the search for exotic physics, such as dark matter.
The significance of the new device stems from its ability to measure rotation and magnetic fields concurrently, which enables orders of magnitude improvement in the sensitivity, said Dr Morgan Hedges, from the Department of Quantum Sciences and Technology (QST).
“Magnetic fields are pervasive, and prevent you making good measurements of rotation.”
“This co-magnetometer is a fresh way of looking at this magnetic noise problem and has the potential to overcome the limitations that have haunted us for decades,” said Dr Hedges, who is the lead author on a paper reporting the design in New Journal of Physics.
The device detects rotations and magnetic fields via the quantum spin – a similar mechanism to Magnetic Resonance Imaging (MRI) - which is exquisitely sensitive to magnetic driving and rotations.
The technique uses a mixture of two gases in a glass cell; an alkali gas, which interacts with the laser beam, and a noble gas, which is invisible to the laser – like a ghost. This enables the rotation and the magnetic field, which both affect the behaviour of the atoms, to be individually deduced.
Professor Ben Buchler, also from QST, said the rotation and magnetic field can be individually deduced because of the interactions between the atomic species, and their different response to magnetic fields.
“Although the spins of both gases rotate around each other, the laser system only sees the alkali spin. The noble gas is invisible but reacts to magnetic field of the alkali – it’s like a ghost, whose presence is only revealed by the way the spin of the alkali dances around it,” Professor Buchler said.
The key to separating the magnetic effects from the rotation is exposing the gas mixture to synchronised pulses of both laser light and magnetic field. The laser pulses drive only the alkali via electron spin, whereas the magnetic pulses drive only the noble gas’s nuclear spin. After the pulses are applied, the motion of the alkali spin is measured and can be used to reveal the spin of both species of gas.
The team alternated the polarity of magnetic field pulses and measured the alkali’s precession signal between pulses, which gave enough information to separate out four quantities – rotation and magnetic field in both x and y directions.
Better yet, the precession signal is very sensitive to the alignment of the magnetic field to the laser, which helps optimise the set up, and could be used as sensitive feedback for automated correction of alignment.
The team successfully tested a prototype device, using xenon-129 and rubidium-87, giving them confidence that the device should be able to achieve sensitivity that is as good as or better than current technology of both magnetometers and gyroscopes. It is also compact and low-power – for example, it does not need cryogenic temperatures.
Professor Buchler said the co-magnetometer could be useful in the search for light dark matter particles, known as axions.
“In some models of dark matter, axions could cause some spin precession, and our technique would allow us to examine that,” he said.
“The relative strengths of the rotation and the magnetic field would give you information about the dark matter particles.”
“It’s a table top experiment that would allow you to search for new physics at the lab scale, without the need for a billion-dollar collider.”
The QST group is part of an international collaboration of similar experiments looking for dark matter, Global Network of Optical Magnetometers for Exotic Physics Searches or GNOME.
Professor Buchler said that, as well as the hunt for dark matter, the new device will likely open many other avenues of exploration.
“No one has thought of a measurement system quite like this before, so every application we think of is new!”
This article was first published by the ANU Research School of Physics.
