To make some of the most accurate measurements of the world around us, scientists tend to go small – down to the atomic scale using a technique called atomic interferometry.
For the first time, scientists performed this type of measurement in space using a sounding rocket specially designed to transport scientific payloads in the lowlands.
This is an important step towards the implementation of matter-wave interferometry in the space for scientific applications ranging from fundamental physics to navigation.
“We have established the technological basis for atomic interferometry aboard a sounding rocket and have shown that such experiments are possible not only on Earth but also in space,” said physicist Patrick Windpassinger of the Johannes Gutenberg University of Mainz in Germany. said.
Interferometry is a relatively simple concept. You take two identical waves, separate them, recombine them and use the small difference between – what is called a phase shift – to measure the force caused by the distance.
This is called an interference pattern. A well-known example is the LIGO light interferometer, which measures gravitational waves: A ray of light divides tunnels two kilometers long, jumps off the mirrors and recombines. The resulting disturbance pattern can be used to detect the gravitational waves caused by black holes that collide millions of light-years away.
Atomic interferometry, which uses the wave-like behavior of atoms, is a little harder to achieve, but has the advantage of a much smaller device. It will be very useful in space, where it can be used to measure things like gravity to a high level of precision; so, a team of German researchers has been working for years to make this happen.
The first step is to create a state of matter called a Bose-Einstein condensate. It is formed from atoms that are cooled to just a fraction above absolute zero (but do not reach absolute zero, on which atoms no longer move). It lowers them to their lowest energy state, moves very slowly and overlaps in quantum superposition – and produces a high density cloud of atoms that acts like one ‘superatom’ or matter wave.
This is an ideal starting point for interferometry, as the atoms all behave the same, and the team achieved the creation of a Bose-Einstein condensate in space for the first time using their resounding rocket in 2017, with a gas rubidium atoms.
“For us, this ultra-cold ensemble represents a very promising starting point for atomic interferometry,” Windpassinger said.
For the next phase of their research, they had to separate and recombine the upper atoms. Once again, the researchers created their rubidium Bose-Einstein condensate, but this time they used lasers to irradiate the gas, causing the atoms to separate and then reunite in superposition.
Interference patterns observed in the Bose-Einstein condensate. (Lachmann et al., Nat. Commun., 2021)
The resulting interference pattern showed a clear influence by the micro-gravity environment of the sounding rocket, suggesting that the technique could be used with a little refinement to measure this environment with high precision.
The next step of the research, planned for 2022 and 2023, is to retry the test using separate Bose-Einstein condensates of rubidium and potassium to observe their acceleration under free fall.
Since rubidium and potassium atoms have different masses, the experiment, according to the researchers, will be an interesting test of Einstein’s equivalence principle, which states that gravity accelerates all objects equally fast, regardless of their own mass.
The principle has been previously investigated in space, as can be seen in the famous spring 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 break down in the quantum range, and therefore the planned experiments will indeed be very interesting.
And it’s only going to get more interesting in the future. Sounding rockets rise and fall in suborbital flights, but more Bose-Einstein condensate experiments are planned to be conducted in Earth orbit.
“Performing these types of experiments would be a future goal on satellites or the International Space Station ISS, possibly within BECCAL, the Bose Einstein condensate and cold atomic laboratory, which is currently in the planning phase,” said physicist André Wenzlawski of the Johannes Gutenberg University said. Mainz in Germany.
“In this case, the achievable accuracy would not be limited by the limited free-fall time aboard a rocket.”
In a few years, we can use atomic interferometry for applications such as quantum tests of general relativity, the detection of gravitational waves and even the search for dark matter and dark energy.
We can not wait to see what happens next.
The team’s research was published in Nature communication.