In our everyday world, measuring time is as easy as looking at a watch or counting the seconds between two events. But zoom down to the quantum scale, where electrons blur and behave more like probabilities than particles, and traditional methods of tracking time break down. A stopwatch won’t cut it when now and then start to blur into uncertainty.
A groundbreaking study from Uppsala University in Sweden, published in Physical Review Research in 2022, offers a new solution: measuring time through the shape of quantum waves. Instead of starting a clock, this novel technique reads the unique patterns of quantum interference left behind by atoms pushed into extreme energy states known as Rydberg states.
Think of Rydberg atoms as the inflated balloons of the quantum world, electrons orbiting far from the nucleus after being zapped by lasers into exaggerated energy levels. These super-sized atomic structures are already familiar territory in quantum tech, especially in the development of quantum computers.
What the Uppsala research team discovered is that these atoms don’t just jump randomly between states. They form wave-like patterns, Rydberg wave packets, which ripple and interfere like waves on a pond. When several of these wave packets are generated, their interference patterns act like fingerprints of time, unique signatures that reveal how long the quantum system has been evolving, without needing a defined start point.
Lead physicist Marta Berholts explained it best: “If you’re using a counter, you have to define zero. You start counting at some point. The benefit of this is that you don’t have to start the clock – you just look at the interference structure and say ‘okay, it’s been 4 nanoseconds.’”
To test their method, the researchers excited helium atoms with lasers and observed the resulting interference patterns. By matching their results with theoretical predictions, they confirmed that these patterns could indeed stand in for a traditional time measurement.
It’s a bit like timing a race where you don’t know when the runner started, but you do know the speeds of all other runners. By comparing where they all are at any moment, you can backtrack how long the unknown runner has been on the track. In this case, the runners are Rydberg wave packets interfering in a precise, readable pattern.
These quantum timestamps are so fine-tuned, they can capture events as fleeting as 1.7 trillionths of a second. And because they don’t rely on a defined “start” or “stop,” they’re perfect for ultrafast systems where tracking the beginning of an event is near-impossible.
Looking ahead, the researchers suggest expanding their “quantum time guidebook” by experimenting with different atoms or laser energies, opening up new potential across fields like ultrafast electronics, quantum computing, and fundamental physics.
