Amazing stuff! Food for thought! Can time run simultaneously faster and slower?
"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. ...
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 ... shows that this striking possibility may soon be tested in the laboratory. ...
In this work, a team ... 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. ..."
From the abstract:
"Optical clocks based on atoms and ions probe relativistic effects with unprecedented sensitivity.
They resolve time dilation due to atom motion or different positions in the gravitational potential through frequency shifts. However, all measurements of time dilation so far can be explained effectively as the result of dynamics with respect to a classical proper time parameter.
Here we show that atomic clocks can probe effects where a classical description of the proper time dynamics is insufficient as superpositions of proper time emerge.
We apply a Hamiltonian formalism to derive time dilation effects in harmonically trapped clock atoms and show how second-order Doppler shifts due to the vacuum energy, squeezing, and quantum corrections to the dynamics arise.
We also demonstrate that time-dilation-induced entanglement between motion and clock evolution can become observable in state-of-the-art clocks when the motion of the atoms is strongly squeezed, realizing proper time interferometry.
Our results show that experiments with trapped ion clocks are within reach of probing relativistic evolution of clocks for which a quantum description of proper time becomes necessary."
Illustration of classical, semiclassical, and quantum proper time dynamics of a trapped-ion atomic clock that we consider.
Illustration of time-dilation-induced entanglement between clock and motional degrees of freedom, and how it can be observed using trapped atomic clocks with squeezing of motional states. The protocol proceeds from left to right.
The top row shows the motional states in a phase-space representation, where a squeezed state is prepared which then evolves at different frequencies in superposition, depending on the internal clock states.
The bottom row shows the same sequence from the perspective of the clock degrees of freedom represented on a Bloch sphere, where a Ramsey sequence results in a superposition of different time evolutions of the clocks due to the different motional energies.
The entanglement between motion and clock (last column) causes a reduction in visibility of the clock ... which can be measured with current state-of-the-art ion clock systems.
