Few concepts in physics are as familiar, or as puzzling, as time itself. Einstein’s theory of relativity showed that time is not fixed or universal. Instead, it changes depending on speed and gravity. When scientists combine relativity with quantum mechanics, however, the picture becomes even stranger. Quantum theory suggests that time itself could exist in a superposition, meaning it may flow both faster and slower simultaneously.
A newly published study suggests researchers may soon be able to test this bizarre idea in the lab. The paper, titled “Quantum signatures of proper time in optical ion clocks,” appeared April 20, 2026 in Physical Review Letters. The research was led by Assistant Professor Igor Pikovski of Stevens Institute of Technology, working with experimental teams led by Christian Sanner at Colorado State University and Dietrich Leibfried at the National Institute of Standards and Technology (NIST).
Atomic Clocks and Quantum Time
The researchers explored how advanced atomic clocks could reveal hidden quantum effects connected to the flow of time. According to their findings, the same technologies being developed for next generation clocks and quantum computers may also allow scientists to investigate whether time itself behaves according to quantum rules.
In quantum mechanics, objects can exist in multiple states at once. This concept is famously illustrated by Schrödinger’s cat, a thought experiment in which a cat is considered both alive and dead simultaneously until it is observed. The researchers suggest something similarly strange could happen with time. A clock whose motion follows quantum rules could experience multiple flows of time at the same moment, almost like a cat that is both young and old simultaneously.
“Time plays very different roles in quantum theory and in relativity,” says Pikovski. “What we show is that bringing these two concepts together can reveal hidden quantum signatures of time-flow that can no longer be described by classical physics.”
The Quantum Twin Paradox
Relativity already predicts that time passes differently depending on motion and location. Every clock measures its own unique flow of time. For instance, a clock traveling at 10 m/s for 57 million years would fall behind a stationary clock by about one second. Scientists have confirmed effects like this using highly precise devices such as aluminum-ion clocks at NIST.
This phenomenon is often explained using the “twin paradox,” where one twin travels at high speed and returns younger than the twin who stayed behind. The new study pushes this idea further into the quantum realm.
Researchers asked whether a single clock could experience two different rates of time simultaneously while existing in a quantum superposition. According to quantum theory, that should be possible. Pikovski and his collaborators first proposed the idea more than a decade ago, but the effect was too subtle to observe experimentally at the time. Advances in atomic clock technology may now change that.
Ultracold Ion Clocks and Quantum Fluctuations
The team focused on ion clocks like those being developed at NIST and Colorado State University. These devices trap single ions such as aluminum or ytterbium, cool them to temperatures near absolute zero, and control their quantum states using lasers.
Their analysis showed that combining highly accurate clocks with techniques from trapped-ion quantum computing could make it possible to observe previously hidden quantum properties of time.
“Atomic clocks are now so sensitive, they can detect tiny differences in time caused by just the thermal vibrations at minuscule temperatures,” says Gabriel Sorci, a PhD candidate at Stevens Institute of Technology and co-author of the paper. “But even at the absolute zero temperature, the ground state, the ticking rate will still be affected by just the quantum fluctuations alone.”
The researchers then explored an even more unusual possibility. Instead of simply cooling the atoms, they proposed manipulating the vacuum itself by creating “squeezed states,” quantum states in which position and velocity behave in unusual ways.
Clocks That Tick Faster and Slower at Once
Under these conditions, the team found that entirely new quantum effects involving time could emerge. A single clock could effectively tick both faster and slower at the same time while also becoming entangled with its own quantum motion.
The researchers now hope to demonstrate these effects experimentally.
“We have the technology to generate the required squeezing and a path to reach the clock precision needed in ion clocks to observe such effects for the first time,” says Sanner of Colorado State.
For Pikovski, the broader implications are just as exciting. His previous work includes showing that quantum technology could potentially detect single gravitons, the hypothetical particles thought to carry gravity.
“Physics is still full of mysteries at the most fundamental level. Quantum technologies are now giving us new tools to shed light on them.”
