Scientists at Stevens Institute of Technology reveal that time can go quantum in ion clock experiments
Physicists show that atomic clocks can probe time ticking both faster and slower simultaneously, revealing how time itself unfolds in quantum superposition.
Stevens Institute of Technology
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Trapped ions are versatile platforms used for quantum computing and ultra-precise timekeeping. New results now show that combining these capabilities can reveal a deeper layer of physical reality: quantum superpositions of the passage of time.
view moreCredit: Igor Pikovski
HOBOKEN, NJ., April 20, 2026 — Few concepts in physics are as familiar, yet as enigmatic, as time. In Einstein’s theory of relativity, time is not absolute: its passage depends on motion and gravity. But when combined with quantum physics, this relativistic form of time becomes even more counterintuitive. According to quantum theory, the flow of time itself may exist in a genuine quantum superposition, ticking faster and slower at the same time. Now, a new paper titled Quantum signatures of proper time in optical ion clocks, published on April 20, 2026 in Physical Review Letters, the premier physics research journal, shows that this striking possibility may soon be tested in the laboratory.
In this work, a team led by Assistant Professor of theoretical physics Igor Pikovski at Stevens Institute of Technology, in collaboration with experimental groups of Christian Sanner at Colorado State University and Dietrich Leibfried at the National Institute of Standards and Technology (NIST), explores quantum aspects of the flow of time and how they can be accessed with atomic clocks. Their results suggest that the same quantum technologies being developed for next-generation clocks and quantum computers may soon probe something far more fundamental: When a clock’s motion obeys quantum mechanics, its movement can exist in superposition, and with it the recorded passage of time itself. This is analogous to Schrödinger’s famous thought experiment, where the counterintuitive nature of quantum superposition is illustrated by a cat being both alive and dead; here it is the passage of time itself that is in superposition, like a cat that is both young and old at once.
“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.”
In relativity theory, every clock experiences its own flow of time, which in turn depends on velocity and position. For example, a clock moving at 10 m/s for 57 million years would lag behind another clock at rest by just one second. This has been observed and confirmed with ultraprecise clocks, such as aluminum-ion clocks at NIST.
The effect is often illustrated as the “twin paradox”: two identical twins will age differently, if one of them takes a high-speed roundtrip. Yet there is a more counterintuitive version: the “quantum twin paradox.” Can a single clock experience two different times in a quantum superposition, and become both younger and older simultaneously? According to quantum theory, as outlined by Pikovski and collaborators over a decade ago, that should happen. So far, such subtle effects have been beyond experimental reach, however, the team’s new theoretical study shows that atomic clocks are now up to the task.
The authors of the now published paper investigated the interplay of relativistic time and quantum effects in atomic clocks, such as those developed at NIST and at Colorado State University where scientists trap single ions (such as aluminum or ytterbium), cooling them to near absolute zero temperature and manipulate their quantum states with laser pulses. The results of their study show that by combining the rapidly improving clock technology with quantum information techniques developed for trapped-ion quantum computing, unique and yet undetected quantum features of time can be observed.
“Atomic clocks are now so sensitive, they can detect tiny differences in time caused by just the thermal vibrations at miniscule 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 team went one step further. Rather than just cooling the atoms, they show that one can instead manipulate the vacuum itself, creating so-called squeezed states in which the position and velocity of the clock exhibit subtle quantum behavior. The result is a new manifestation of relativistic time in the quantum regime, where superpositions and entanglement of time arise: a single clock can measure how it ticks both faster and slower simultaneously, and entangle with the squeezed motion. The team now aims to demonstrate the effects in the laboratory.
“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, whose recent work includes showing that single gravitons can be detected using quantum technology, points to the bigger picture. “Physics is still full of mysteries at the most fundamental level. Quantum technologies are now giving us new tools to shed light on them.”
About Stevens Institute of Technology
Stevens is a premier, private research university situated in Hoboken, New Jersey. Since our founding in 1870, technological innovation has been the hallmark of Stevens’ education and research. Within the university’s three schools and one college, more than 8,000 undergraduate and graduate students collaborate closely with faculty in an interdisciplinary, student-centric, entrepreneurial environment. Academic and research programs spanning business, computing, engineering, the arts and other disciplines actively advance the frontiers of science and leverage technology to confront our most pressing global challenges. The university continues to be consistently ranked among the nation’s leaders in career services, post-graduation salaries of alumni and return on tuition investment.
Journal
Physical Review Letters
Article Title
Quantum signatures of proper time in optical ion clocks
Article Publication Date
20-Apr-2026
Water simulation of famous quantum effect reveals unexpected wave patterns
A new study reveals how a spinning vortex causes system-wide, counter-rotating wave patterns, mimicking effects that occur, but cannot be seen, in the quantum realm.
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Lines of momentarily flat water extend outward and rotate, in the opposite direction to the flow of the vortex. The left video shows the pattern from the experiment, while the right video shows the same effect in a simulation model.
view moreCredit: Singh et. al., (2026) Commun Phys.
In the quirky, quantum world, particles can be affected by forces that they never directly encounter. A classic example is the Aharonov–Bohm (AB) effect, where electrons are affected by a magnetic field, despite not passing through it. Although predicted in 1959, it took more than two decades to confirm this effect experimentally, as the specific changes to the electrons’ wave properties could only be inferred indirectly, and with great difficulty.
Now, physicists from the Okinawa Institute of Science and Technology (OIST), in collaboration with the University of Oslo and Universidad Adolfo Ibáñez, have used a classical fluid analogue that mimics and extends the AB effect using a simple platform: a water tank. Published today in Communications Physics, the researchers have revealed that when water waves are sent towards a swirling vortex from opposite directions, it causes a striking pattern, with one or more lines of momentarily still water radiating outward and rotating in an almost hypnotic way.
“This was something new and unexpected,” says Aditya Singh, a PhD student in the Nonlinear and Non-equilibrium Physics Unit and co-first author of the study. “That’s what makes this fluid analogue system so valuable. It reveals topological effects — wave behaviors that occur across the whole system — that can’t be seen in quantum experiments.”
The beginnings with Berry
The team’s inspiration for this research traces back to a 1980 study by theoretical physicist Michael Berry, who first showed that the AB effect could be simulated in a classical fluid system. In the quantum version, electrons pass around a tightly coiled wire, called a solenoid. When an electric current flows through the solenoid, this generates a magnetic field that’s confined within the coil. However, electrons passing outside the solenoid, where the magnetic field is zero, are still affected, with their wave shifting in phase.
In Berry’s experiment, a vortex forming at the drain of a tank stood in for the solenoid. Instead of electrons, Berry caused water waves to travel across his tank, passing around the vortex rather than through it. The travelling waves developed a distinctive distortion — a pitchfork-like pattern centered on the vortex — marking a shift in their phase.
“With waves travelling the opposite direction, you see a mirror image pattern,” adds Jonas Rønning, co-first author and former postdoc in the OIST unit. “The question for us was: what happens if you send waves from both directions at the same time? We thought that the patterns might cancel each other out, or both pitchfork-like patterns would be visible, but our intuition was completely wrong.”
From travelling to standing waves
In their experiment, the researchers created a vortex at the center of a large, custom-built water tank and generated waves from opposite sides of the tank so that they met and interfered. By illuminating the water’s surface from beneath and recording with a high-speed camera, the team could track how the wave pattern across the whole tank changed over time.
Under conditions without a vortex, when opposing waves meet and interfere, this results in a predictable standing wave pattern where waves appear to be fixed in place. These patterns contain stationary lines, known as wavefronts, where the waves have the same phase.
But adding a vortex gives an unexpected twist. As the vortex causes shifts in the wave phase, this changes how the standing waves interfere with each other, resulting in rotating lines where the wave height is zero, called nodal lines.
“When we first saw these lines, we thought they were an experimental artefact,” says Singh. “But when we also saw them in our simulations, we dropped everything and quickly worked out the mathematics underlying how they arise.”
These nodal lines exhibit interesting behaviors, always rotating in the opposite direction to the vortex, and increasing in number as the researchers increased the vortex’s flow.
At such an early stage of discovery, it’s unclear whether these nodal lines could have useful applications. But for the unit head and senior author, Professor Mahesh Bandi, the real draw is the limitless avenues now open for future research using their classical analogue system. “One direction is to make the system more complex by introducing multiple vortices and arranging them into a lattice,” says Bandi. “That setup would mirror conditions in some superconducting materials, with the water waves behaving like a supercurrent. We don’t yet know what we’ll see — and that’s exactly what makes it worth doing.”
More broadly, the team’s findings highlight the power of simple classical analogues to reveal new understanding about the quantum world. “Theorists might predict these effects, but quantum experiments wouldn’t see them,” he says. “With analogues like this, we can.”
Journal
Communications Physics
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
Topology made visible through standing waves in a spinning fluid
Article Publication Date
20-Apr-2026
Recreation of Berry’s travelling waves [VIDEO]
As waves travel past the vortex, they distort and form pitchfork-like patterns, that are localized around the central vortex. When the direction of the waves is changed (arrow direction), the distortion pattern is mirrored. The top two sections show simulated patterns while the bottom two sections show the patterns seen in the experiments.
Credit
Singh et. al., (2026) Commun. Phys.
Credit
Waurids Baskurtf, Wikimedia Commons, CC BY-SA 2.5
The research team custom-built a water tank with a high-speed camera above to detect wave patterns on the water’s surface.
Credit
Andrew Scott / OIST
OIST PhD student Aditya Singh generates and observes surface waves that act as a classical analogue to quantum effects.
Credit
Andrew Scott / OIST
Number of nodal lines is linked to vortex flow [VIDEO]
In both simulations (above) and experiments (below), the number of rotating nodal lines increases with a faster vortex flow. At lower flow (left), only one nodal line is seen, whilst at a higher flow (right), two nodal lines appear.
Credit
Singh et. al., (2026) Commun. Phys.
