Researchers at MIT say they have discovered a way to double the precision of optical atomic clocks by quieting the quantum noise that clouds their ticking.
Atomic clocks keep time by monitoring the natural oscillations of atoms as they move between energy states.
Each atom oscillates unimaginably fast. Cesium, for instance, vibrates more than 10 billion times every second. By locking lasers (in optical atomic clocks) or microwaves (in “traditional” atomic clocks) to those frequencies, scientists can measure time down to billionths of a second.
The problem is that atoms are, unsurprisingly, incredibly difficult to measure. As well as being very, very tiny, quantum mechanics builds in a sort of microscopic static that makes their ticking impossible to measure with complete certainty.
The MIT team discovered a way to tune out that static using a technique they call global phase spectroscopy, which they described in a new study published in Nature.
It involves shining laser light through a cloud of entangled atoms and measuring tiny changes in their collective behavior. When the light passes through the atoms, it briefly nudges them to a higher energy state before they fall back again. As they do, the atoms retain a faint “memory” of the interaction, called a global phase.
Scientists had long assumed this effect was irrelevant, but the team at MIT discovered that it actually carries useful information about the laser’s frequency. Using this information, they were able to more precisely stabilize the laser used to measure the atomic clock’s ticking, effectively doubling its accuracy.
“The laser ultimately inherits the ticking of the atoms,” said first study author Leon Zaporski. “But in order for this inheritance to hold for a long time, the laser has to be quite stable.”
That stability is difficult to achieve because optical atomic clocks operate at vastly higher frequencies than their microwave-based counterparts. “When you have atoms that tick 100 trillion times per second, that’s 10,000 times faster than the frequency of microwaves,” explained study author Vladan Vuletić, a professor of physics at MIT.
It’s hoped the discovery could finally make optical atomic clocks small and stable enough to move out of labs and into the field. “With these clocks, people are trying to detect dark matter and dark energy, and test whether there really are just four fundamental forces, and even to see if these clocks can predict earthquakes,” said Vuletic.
“We think our method can help make these clocks transportable and deployable to where they’re needed.”
