Atomic clocks multiply precision by breaking the limit of energy consumption

Nanotechnology

Technological Innovation Website Editorial Team - 06/16/2025

Artist's impression of the Ring Clock, constructed from a ring of atoms, enabling ultra-precise timekeeping. A single quantum particle circles the ring coherently - each revolution is a tick - allowing the clock to overcome the thermodynamic limitations of classical clocks. [Image: Alexander Rommel/TU Wien]

More accurate quantum clocks

A team of physicists and engineers from Austria, Malta and Sweden has discovered that atomic clocks , already by far the most accurate devices in existence, can take a leap in accuracy without having to expend a huge amount of energy.

Florian Meier and his colleagues have demonstrated that it is possible to far exceed the accuracy limits assumed so far, increasing temporal precision exponentially. This will not only pave the way for the next generation of high-precision measurements and monitoring of ultrafast events, but also sheds light on one of the greatest mysteries in physics: the connection between quantum physics and thermodynamics .

Atomic clocks operate based on the fundamental laws of quantum physics, but these laws always involve a degree of uncertainty. As a result, it is necessary to live with some randomness, a certain level of statistical noise, which results, in the case of clocks, in fundamental limits to the precision that can be achieved for a given energy expenditure.

So until now it seemed to be an immutable law that building a clock twice as accurate as the previous one would require at least twice as much energy.

What the team has now demonstrated is that this rule can be circumvented to increase the accuracy of an atomic clock exponentially, simply by building an atomic clock using two different time scales - similar to what happens in a regular clock, which has a second hand and a minute hand.

• Quantum theory and thermodynamics can live in harmony, even if they disagree

The clock consists of a ring of n quantum systems (the "cups") that host a single excitation that travels around the ring. When completing a cycle, the clock ticks by jumping from the last to the first site. [Image: Florian Meier et al. - 10.1038/s41567-025-02929-2]

Why does measuring time increase entropy?

To understand the relationship between precision in time measurement and energy consumption, it is necessary to remember that measuring time increases the entropy of the Universe .

Any clock consists of two components, a time base generator, which can be a pendulum or the oscillations of an atom, and a counter, any mechanism that counts how many times that base unit of time has elapsed.

The time base generator can always return to exactly the same state: After one complete oscillation, the pendulum of a pendulum clock is exactly where it was before; after a certain number of oscillations, the cesium atom in an atomic clock returns to exactly the same state it was in before. The counter, on the other hand, must change, otherwise the clock is useless.

"This means that every clock must be connected to an irreversible process," explains Professor Florian Meier from the Technical University of Vienna. "In the language of thermodynamics, this means that every clock increases the entropy, or dispersion of energy, in the Universe; otherwise, it is not a clock."

The pendulum of a classical clock generates a little heat and disorder among the air molecules around it, and each laser beam that reads the state of an atomic clock generates heat, radiation and therefore entropy.

"We can now consider how much entropy a hypothetical clock with very high precision would have to generate - and therefore how much energy such a clock would need," explains Professor Marcus Huber. "Until now, there seemed to be a linear relationship: If you want a thousand times more precision, you need to generate at least a thousand times more entropy and use a thousand times more energy."

• Quantum Thermodynamics: Entropy may indeed exist in the quantum world

The stars of current precision, which will also benefit from this discovery, are optical quantum clocks . [Image: Physikalisch-Technische Bundesanstalt]

How to increase accuracy without increasing entropy

Now, however, everything has changed. While the same idea from the previous section still holds true, the team has discovered that it is possible to get around it with a simple trick: Using two different time scales, just as an analog clock has minute and second hands.

In fact, it is possible to add a whole series of secondary time-measuring devices, and then count how many of them have passed - similar to how a minute hand counts how many revolutions the second hand has made, or the hour hand counts how many revolutions the minute hand has completed.

In a classical clock, this increase in scale also increases the entropy, which is generated when one hand moves to a new location as the other has made a revolution. In other words, increasing precision requires spending more energy. However, quantum physics also allows for another type of particle transport: The particles can travel throughout the entire structure, that is, across the entire clock face, without being measured anywhere. In a sense, the particle is everywhere at once during this process; it does not have a clearly defined location until it finally arrives - and only then is it actually measured, that is, only this part of the whole process is irreversible, increasing entropy.

"In this way, we have a fast process that does not cause entropy - quantum transport - and a slow one, namely the arrival of the particle at the very end," explains Yuri Minoguchi, a member of the team. "The crucial point of our method is that one side behaves purely in terms of quantum physics, and only the other, slower side, has an entropy-generating effect."

The result is that this strategy allows an exponential increase in the accuracy of the atomic clock with each increase in entropy. This means that much greater accuracy can be achieved than previously thought using previous theories.

"This is an important result for research into high-precision quantum measurements and suppression of unwanted fluctuations, and at the same time it helps us to better understand one of the great unsolved mysteries of physics: The connection between quantum physics and thermodynamics," concluded Huber.

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