Placed in a magnetic field, an atom wobbles like a top, but a compass needle simply points in a fixed direction. A research team has now shown theoretically that a compass needle actually does wobble in a sufficiently weak field and that this effect could be exploited to make a super-sensitive magnetic field sensor (magnetometer). Their calculations show that such a device could be 1000 times more sensitive than today’s best magnetometers. Researchers say that this connection between macroscopic and quantum-scale magnets could lead to new magnetometry techniques.
An extremely sensitive magnetometer, shielded from known magnetic fields, could be used to look for previously undetected fields predicted by as-yet unverified theories of quantum gravity or dark matter. With better precision, “you never know what you could find,” says Derek Jackson Kimball of California State University, East Bay.
The idea for a magnetometer was born when Jackson Kimball and his colleagues wondered why a compass needle behaves differently than an atom in a magnetic field. When a glass cell of atomic gas is placed in a magnetic field, the atoms’ spin vectors wobble in circles like slanted spinning tops, a phenomenon known as Larmor precession. Today’s best magnetometers measure the frequency of this precession to determine the field strength, down to about a trillion times smaller than the Earth’s field. But a compass needle doesn’t precess. “When I was out in the woods as a Boy Scout, my compass needle always just lined up at north, along the magnetic field,” Jackson Kimball says. To understand the two different behaviors, he and his colleagues modeled a compass needle theoretically and then realized that they could design an extremely sensitive magnetometer based on their results.
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