To make some of the most accurate measurements we can make of the world around us, scientists tend to reduce themselves to the atomic scale, using a technique called atomic interferometry.
Now, for the first time, scientists have performed this type of measurement in space using a sound rocket specially designed to carry scientific payloads into low Earth space.
It is a significant step towards performing interferometry of matter waves in space, for scientific applications ranging from fundamental physics to navigation.
“We have laid the technological foundations for the interferometry of atoms aboard a sounding rocket and we have shown that these experiments are not only possible on Earth but also in space,” said University physicist Patrick Windpassinger Johannes Gutenberg from Mainz to Germany.
Interferometry is a relatively simple concept. Take two identical waves, separate them, recombine them, and use the small difference between – called phase shift – to measure the force that caused this distance.
This is called an interference pattern. A famous example is the LIGO light interferometer that measures gravitational waves: a beam of light splits into two kilometers-long tunnels, bounces off mirrors, and recombines. The resulting interference pattern can be used to detect gravitational waves caused by the collision of black holes millions of light-years away.
Interferometry of atoms, taking advantage of the behavior of atoms in the form of a wave, is a little more difficult to achieve, but has the advantage of a much smaller apparatus. It would be very useful in space, where it could be used to measure things like gravity at a high level of accuracy; therefore, a team of German researchers has been working for years to try to make this happen.
The first step is to create a state of matter called the Bose-Einstein condensate. These are formed from cooled atoms to only a fraction above absolute zero (but which do not reach absolute zero, at which point the atoms stop moving). This causes them to sink to their lowest energy state, moving extremely slowly and overlapping in the quantum overlap, producing a cloud of high-density atoms that acts as a “super atom” or wave. of matter.
This is an ideal starting point for interferometry, because all atoms behave identically and the team managed to create a Bose-Einstein condensate in space for the first time with its sound rocket on 2017, with a gas of rubidium atoms.
“For us, this ultra-cold set represented a very promising starting point for the interferometry of atoms,” Windpassinger said.
For the next stage of their research, they had to separate and recombine the superimposed atoms. Once again, the researchers created their Bose-Einstein rubidium condensate, but this time they used lasers to irradiate the gas, causing the atoms to separate, to become overlapping together.
Interference patterns observed in the Bose-Einstein condensate. (Lachmann et al., Nat. Commun., 2021)
The resulting interference pattern showed a clear influence of the microgravity environment of the sonar rocket, suggesting that with some refinement, the technique could be used to measure this environment with high accuracy.
The next step in the research, scheduled for 2022 and 2023, is to retest the test using separate Bose-Einstein ruby and potassium condensates to observe its free-falling acceleration.
Because the rubidium and potassium atoms have different masses, this experiment will be, according to the researchers, an interesting proof of Einstein’s principle of equivalence, which states that gravity accelerates all objects equally, regardless of their own mass. .
The principle has been investigated before in space, as can be seen in the famous feather and hammer experiment conducted by Apollo 15 commander David Scott on the Moon. The equivalence principle is one of the cornerstones of general relativity and relativity tends to decompose in the quantum realm, so the predicted experiments are really very interesting.
And it will only be more interesting in the future. Sound rockets go up and down in suborbital flights, but there are plans to conduct even more Bose-Einstein condensate experiments in Earth orbit.
“Undertaking this type of experiment would be a future goal on satellites or the International Space Station’s ISS, possibly within BECCAL, Bose Einstein’s condensing and cold atom laboratory, which is currently in the planning phase. “said physicist André Wenzlawski of Johannes Gutenberg University. Mainz in Germany.
“In this case, the accuracy achievable would not be limited by the limited time of free fall aboard a rocket.”
In a few years, we could use atomic interferometry for applications such as general relativity quantum testing, gravitational wave detection, and even the search for dark matter and dark energy.
We can’t wait to see what happens next.
The team’s research has been published in Communications on Nature.