Marking the passage of time in a world of ticking clocks and swinging pendulums is simply counting the seconds between ‘then’ and ‘now’.
However, down the quantum scale of buzzing electrons, ‘then’ cannot always be foreseen. Even worse, “now” often fades into a blur of uncertainty. A stopwatch just won’t cut it in some scenarios.
According to researchers at Uppsala University in Sweden, a possible solution could be found in the form of the quantum fog itself.
Their experiments on the wave-like nature of something called a Rydberg state have revealed a new way to measure time that doesn’t require a precise starting point.
Rydberg atoms are the over-inflated balloons of the particle kingdom. Blown up with lasers instead of air, these atoms contain electrons in extremely high energy states, orbiting far from the nucleus.
Of course, not every pump from a laser has to blow up an atom to cartoonish proportions. In fact, lasers are routinely used to tickle electrons to higher energy states for a variety of purposes.
In some applications, a second laser can be used to monitor the changes in the electron’s position, including the passage of time. For example, these ‘pump-probe’ techniques can be used to measure the speed of certain ultra-fast electronics.
Inducing atoms into Rydberg states is a handy trick for engineers, not least when it comes to designing new components for quantum computers. Needless to say, physicists have accumulated a considerable amount of information about the way electrons move when pushed into a Rydberg state.
But because they’re quantum animals, their movements aren’t so much like beads sliding around on a tiny abacus, but more like an evening at the roulette table, where every toss and jump of the ball is squeezed into a single game of chance.
The mathematical rule book behind this wild game of Rydberg electron roulette is called a Rydberg wave packet.
Like real waves in a pond, having more than one Rydberg wave pack rippling in a space creates interference, resulting in unique patterns of ripples. Throw enough Rydberg wave packets into the same atomic pond, and those unique patterns each represent the different time it takes for the wave packets to evolve in concert with each other.
It was precisely these “fingerprints” of time that the physicists behind this latest set of experiments set out to test, demonstrating that they were consistent and reliable enough to serve as a form of quantum timestamp.
Their research involved measuring the results of laser-excited helium atoms and matching their findings with theoretical predictions to show how their signature results could hold up over time.
“When you use a counter, you have to define zero. At some point you start counting,” explains physicist Marta Berholts of Uppsala University in Sweden, who led the team. New scientist.
“The advantage of this is that you don’t have to start the clock – you just look at the interference structure and say ‘okay, it’s already 4 nanoseconds.'”
A guide to evolving Rydberg wave packets could be used in conjunction with other forms of pump-probe spectroscopy that measure small-scale events when occasionally less clear or simply too tricky to measure.
Importantly, none of the fingerprints need a then and now to serve as a starting and stopping point for time. It would be like measuring the race of an unknown sprinter against a number of competitors running at fixed speeds.
By looking for the signature of interfering Rydberg states amid a sample of pump-probe atoms, engineers were able to observe a timestamp for events as fleeting as just 1.7 trillionths of a second.
Future quantum watch experiments could replace the helium with other atoms, or even use laser pulses of different energies, to expand the time-stamp guide to suit a wider range of conditions.
This research was published in Physical assessment examination.