# Kyushu University team proposes theory for detecting superposed proper time with trapped-ion optical clocks

- Published: 2026-11-15 19:53 UTC
- Section: Science › Physics
- Tags: optical ion clocks, proper time interferometry, quantum time dilation, superposition of proper time, motion and clock entanglement, squeezed motion, second-order Doppler shift, Kyushu University, Physical Review Letters
- URL: https://realtech.media/news/rt-21ac3cabfaaa5715aa636ead_kyushu_university_team/

**A theoretical study shows that trapped-ion optical clocks could reveal entanglement between atomic motion and clock evolution, a quantum effect of time dilation, using existing experimental technology.**

![Kyushu University team proposes theory for detecting superposed proper time with trapped-ion optical clocks](https://realtech.media/media/2026/11/33b06913c993e722.jpg)
*National Institute of Standards and Technology - Physics Laboratory: Time and Frequency Di, Wikimedia Commons, Public domain*

A team led by Kyushu University, with collaborators in the United States, Canada and Sweden, has described how optical clocks based on trapped ions could detect quantum effects of proper time. The theoretical work by Gabriel Sorci, Joshua Foo, Dietrich Leibfried, Christian Sanner and Igor Pikovski was published on 20 April 2026 in Physical Review Letters. [1] It is a theoretical framework; the effect has not yet been observed in an experiment.

## Why time dilation needs a quantum description

Optical clocks resolve relativistic time dilation, caused by atomic motion or by different positions in the gravitational potential, as frequency shifts. Raising a clock by a few millimeters makes it tick slightly faster, and the best clocks can detect this difference. [1] According to the authors, all such measurements so far can be explained as dynamics with respect to a classical proper time parameter. [1]

The team shows that atomic clocks can probe effects for which this classical description is insufficient, because superpositions of proper time emerge. [1] The authors applied a Hamiltonian formalism to harmonically trapped clock atoms. From it they derived second-order Doppler shifts due to the vacuum energy, squeezing, and quantum corrections to the dynamics. [1]

If the motion of the atom is in a superposition of states, the clock can experience several rates of time at once. In that case the motion becomes entangled with the clock's internal energy. Foo, an associate professor at Kyushu University's Institute for Advanced Studies, said the signature of this entanglement is that the clock loses some of its quantum properties, which can be detected with modern techniques.

## Squeezed motion and proper time interferometry

The authors show that this entanglement between motion and clock evolution can become observable in state-of-the-art clocks when the motion of the atoms is strongly squeezed. This regime realizes proper time interferometry. [1] They conclude that experiments with trapped-ion clocks are within reach of probing relativistic evolution for which a quantum description of proper time becomes necessary. [1]

The team also developed a theoretical approach to controlling the motion of trapped ions. According to the authors, it improves sensitivity to the effect by 100 to 1000 times. The proposed approach relies on existing experimental technology.

The next step is an experiment that can reliably detect the predicted signature while accounting for disturbances and uncertainties in real laboratory conditions. Foo also said the group is interested in whether atomic clocks could eventually probe the quantum realm of gravity.

## Sources

1. [Physical Review Letters](https://doi.org/10.1103/qhj9-pc2b)
2. [SciTechDaily](https://scitechdaily.com/scientists-uncover-a-bizarre-quantum-effect-where-time-could-flow-at-different-speeds-simultaneously)

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Source: RealTech, realtech.media — https://realtech.media/news/rt-21ac3cabfaaa5715aa636ead_kyushu_university_team/