According to quantum theory, the passage of time itself may exist in a quantum superposition state, "flowing" simultaneously at both faster and slower rates. This concept, long confined to theoretical speculation, is now expected to be experimentally verified using advanced atomic clock technology. Researchers from Stevens Institute of Technology in the United States published their findings on the 20th in the journal Physical Review Letters.

In relativity, each clock possesses its own "proper time," the rate of which depends on its velocity and position. Such effects have been verified by ultra-high-precision atomic clocks. However, there exists a more counterintuitive version, known as the "quantum twin paradox": Can a clock, existing in a quantum superposition, simultaneously experience two different rates of time passage, thereby being both "younger" and "older"?

According to a theory proposed over a decade ago by Pikovski and his collaborators, such a scenario is possible within the quantum framework. Yet, until now, this extremely subtle effect has remained difficult to observe experimentally.

The latest research indicates that as the precision of atomic clocks continues to improve, this long-theoretical effect is gradually entering the realm of detectability. In the experiment, researchers trapped single ions (such as aluminum or ytterbium ions), cooled them to near absolute zero, and precisely manipulated their quantum states using laser pulses. The results show that by combining atomic clock technology with the quantum information techniques used for trapped ion quantum computing, quantum properties of time that were never before detected can be observed.

Even at absolute zero, quantum fluctuations still affect a clock's rate of timekeeping. Furthermore, by constructing so-called "squeezed states" to directly manipulate the quantum vacuum, special quantum correlations can be induced between the clock's position and velocity. This leads to the superposition and entanglement of the passage of time—meaning a clock can not only run "fast" and "slow" simultaneously, but also become quantum-entangled with the motion of its "squeezed state."