Ultracold clocks could reveal how quantum physics alters time

What does the passage of time appear like for a truly quantum object? Remarkably, the world’s most advanced clocks may soon shed light on this question, enabling us to examine how time can warp and shift in the quantum realm, thus allowing exploration into uncharted depths of physics.

The concept that the flow of time can alter or dilate originates from Albert Einstein’s revolutionary theories. According to Einstein’s special theory of relativity, as objects travel closer to the speed of light, time appears to slow down for them as compared to a stationary observer. This principle is further extended in his general theory of relativity, where gravitational forces similarly affect the linearity of time.

Igor Pikovski at the Stevens Institute of Technology in New Jersey, along with his research team, aims to understand whether such effects are relevant in the microscopic quantum domain, specifically through the lens of ultracold clocks composed of ions.

“Previously conducted experiments have primarily sensed a notion of classical time—one that does not intersect with quantum phenomena,” states Pikovski. “We discovered a regime where the operation of ion clocks diverges from this interpretation entirely,” he asserts.

These advanced timekeeping devices are constructed from numerous ions cooled to temperatures just above absolute zero, manipulated using lasers. At these extremely low temperatures, the quantum states of the ions and their electrons can be finely tuned via electromagnetic forces, thereby determining the ticking of the clock through the oscillation of electrons between precise quantum states.

Since these clocks are fundamentally governed by quantum mechanics, they create the ideal environment for Pikovski and his team to investigate how relativistic and quantum principles may connect to influence the clocks’ tick rates. They have already pinpointed multiple instances where such phenomena could occur.

One notable example arises from the fact that quantum mechanics inherently avoids a state of absolute stillness. Thus, even at near-zero temperatures, quantum objects experience fluctuations, artificially alternating between gaining and losing energy. The team’s analytical work indicates that these energy fluctuations could lead to the dilation of a clock’s time readings. Although the impact is predicted to be minuscule, it is highly likely to be detectable with current ion clock technology.

Furthermore, the researchers mathematically illustrated the implications of inducing a “superposition” of multiple quantum states within the clock’s ions. Their findings suggested that the ticking rates—dictated by the electron transitions—could become inseperably intertwined with the ions’ motion itself, leading to quantum entanglement between the ions and their electrons. “Normally, achieving entanglement necessitates specific experimental manipulations. The intriguing fact here is that entanglement materializes automatically,” remarks Christian Sanner from Colorado State University.

Pikovski notes that it is intuitively sensible for a quantum object existing in multiple states not to undergo just one absolute perception of time, though this effect has yet to be observed during experiments. He is optimistic that such observations can be made soon.

Gabriel Sorci, also from Stevens Institute of Technology, mentions that the project’s next step is to incorporate an additional critical modern physics component—gravity. Ultracold clocks are presently capable of detecting time dilations caused by slight variations in Earth’s gravitational field, such as when raised just millimeters. However, how this gravitational influence integrates with the intrinsic quantum behavior of the clock remains uncertain.

David Hume from the US National Institute of Standards and Technology in Colorado believes implementing this concept with today’s existing technologies is entirely feasible. He points out that the primary hurdle will be mitigating slight environmental disturbances which could overshadow the phenomena suggested by Pikovski’s research. Successfully navigating these challenges could empower scientists to explore physical phenomena that have previously been beyond reach. Despite quantum theory and relativity being foundational pillars of contemporary physics, the crossing-point between them could uncover unprecedented insights.

“Studies like this are thrilling because they compel these fundamental theories to engage with one another in a realm where novel discoveries could emerge,” adds Alexander Smith at Saint Anselm College in New Hampshire.