'Quantum Radio' -- Reaching the Unreachable

In the 21^st century, it often seems as if there’s no place that telecommunications can’t get to. But in fact, there are many locations where GPS, cell phones, and radios don’t work reliably or even at all, such as indoors, in urban canyons, under water, or underground.

Now PML scientists are pioneering an entirely new quantum technology designed to help mariners, soldiers and surveyors, among others, exchange messages and create maps in forbidding environments.

GPS signals don’t penetrate very deeply or at all in water, soil or building walls, and therefore, can’t be used by submarines or in underground activities such as surveying mines. GPS also may not work well indoors or even outdoors among city skyscrapers. For soldiers, radio signals may be blocked in environments cluttered by rubble or interfering electromagnetic devices during military or disaster recovery missions.

To address those problems, researchers in PML’s Time and Frequency Division are developing systems to detect low-frequency “magnetic radio”—very low frequency digital magnetic signals—which can travel farther through building materials, water, and soil than conventional electromagnetic communications signals at higher frequencies.

The PML team uses glass cells the size of a thimble filled with specially prepared collections of trapped atoms that respond strongly to faint magnetic fields by changing their “spin” state, thus functioning as highly sensitive quantum sensors. In tests so far, the devices measured magnetic field signals as small as one millionth of the Earth’s magnetic field strength and at frequencies well below those typically employed in some government and military services.