We’ve come a long way since the first sundials and hourglasses, a timekeeping journey that first began in ancient Egypt and Babylon more than 5,000 years ago. But although we now have fancy digital watches synchronized through satellites and cesium atomic clocks that lose only one second every 100 million years, their fundamental operating principle is the same as a sundial. But this may soon change.

Recently, scientists introduced a novel time-measuring device that is actually different than any watch that came before it because it lacks “time zero”. Prepare for some quantum weirdness.

A watch in a quantum fog

All conventional time-keeping clocks work by measuring how long it takes to complete a predefined cycle or the period between two intervals. This includes the complete swaying motion of a pendulum or the elapsed time between the starting and finishing position of a person running on a track.

For pretty much all intents and purposes, this works great. Researchers at the University of Uppsala in Sweden and the University of Tartu in Estonia wanted to try out something different, though. What if they could somehow make a watch that requires no initial point of reference, or “T zero”?

Setting out on this ambitious task, the researchers reckoned their best bet was to experiment with atoms in a so-called Rydberg state — a state in which the electrons from atoms become highly excited and are pushed very far away from their nucleus. This high-energy state can be achieved with the help of lasers.

Previous research showed that multiple Rydberg-energized atoms in the same space create interferences that generate unique ripple patterns in the ‘quantum pond’. With enough of these atoms dancing in the same space, you end up with uniquely evolving patterns that each represent the distinct amount of time it took to evolve compared with all the others in the vicinity. I know this is a bit dizzying, but all of this just means they can be used as precise time stamps.

During experiments, the physicists excited helium atoms using a laser, while another laser firing short pulses of ultraviolet light measured the spectrum of the Rydberg state atoms.

The watch could make measurements of up to 81 picoseconds (one trillionth of a second) and had errors no larger than 8 femtoseconds (one quadrillionth of a second). Watch is the keyword here and not a clock, since it doesn’t count time units but only displays the time, which can be deduced by the interference structure. It’s quite a clever way to measure time without having to actually count units of time.

“We show that the oscillations resulting from an ensemble of highly excited Rydberg states” can “give rise to a unique interference pattern that does not repeat during the lifetime of the wave packet,” the team explained in their study. “These fingerprints determine how much time has passed since the wave packet was formed and provide an assurance that the measured time is correct.” 

“Unlike any other clock, this quantum watch does not utilize a counter and is fully quantum mechanical in its nature,” the researchers added.

This novel technique could prove useful in a range of applications in physics, such as those that require high temporal accuracy of the processes observed in quantum mechanical systems.

The findings appeared in the journal Physical Review Research.