Cutting-edge atomic clocks may soon reveal a strange possibility: time itself behaving like a quantum object, existing in multiple states at once.
Few ideas in physics feel as intuitive, yet remain as puzzling, as time. In Einstein’s theory of relativity, time is not fixed. It changes depending on motion and gravity.
When this concept is combined with quantum physics, the picture becomes even stranger. Quantum theory suggests that time itself might exist in a superposition, meaning it could pass at different rates at the same time.
A new study published in Physical Review Letters indicates that this possibility may soon be tested experimentally.
Probing Time With Quantum Clocks
The research was led by Igor Pikovski, an assistant professor of theoretical physics at 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). The team examined how quantum effects influence the flow of time and how atomic clocks can be used to study these effects.
Their findings suggest that technologies developed for advanced clocks and quantum computers could also probe deeper questions about reality. If a clock follows the rules of quantum mechanics, its motion can exist in multiple states at once. As a result, the time it measures could also exist in multiple states.
This idea resembles Schrödinger’s well-known thought experiment, where a cat can be both alive and dead. In this case, time itself would exist in overlapping states, as if a clock were both younger and older at the same moment.
“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.”
Relativity, Motion, and the Flow of Time
Relativity predicts that every clock measures time differently depending on its speed and position. For instance, a clock moving at 10 meters per second (about 22 miles per hour) for 57 million years would fall behind a stationary clock by only one second. Experiments with highly precise devices, including aluminum ion clocks at NIST, have confirmed this effect.
This phenomenon is often explained using the “twin paradox,” where one twin ages more slowly after traveling at high speed. A more extreme version, sometimes called the “quantum twin paradox,” asks whether a single clock could experience multiple timelines at once. Could it be both younger and older at the same time? Earlier theoretical work by Pikovski and his colleagues suggests this is possible, although such effects have been too subtle to measure until now.
Atomic Clocks Enter the Quantum Regime
To investigate this idea, the researchers studied atomic clocks like those at NIST and Colorado State University. These systems trap single ions, such as aluminum or ytterbium, cool them to nearly absolute zero, and control their quantum states with lasers.
The study shows that combining advances in clock precision with techniques from trapped ion quantum computing could reveal previously unseen quantum effects in time itself.
“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.”
Squeezing the Quantum Vacuum
The team also explored a more advanced approach. Instead of only cooling atoms, they propose manipulating the quantum vacuum to create “squeezed states.” In these states, the position and motion of the clock show distinct quantum behavior.
This leads to a new way of understanding time under quantum conditions. A single clock could measure itself ticking at different rates at once and become linked, or entangled, with its own motion. The researchers are now working toward testing these predictions in the lab.
“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.
Looking ahead, Pikovski points to broader implications. His recent research includes work suggesting that single gravitons could be detected using quantum technology. “Physics is still full of mysteries at the most fundamental level. Quantum technologies are now giving us new tools to shed light on them.”
Reference: “Quantum Signatures of Proper Time in Optical Ion Clocks” by Gabriel Sorci, Joshua Foo, Dietrich Leibfried, Christian Sanner and Igor Pikovski, 20 April 2026, Physical Review Letters.
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