Researchers create the ‘atomic telescope’ that may slow atoms to a standstill

Understanding the fundamental mechanics that define the transition between the quantum state and the classical state that defines our observable physical reality continues to prove challenging. It’s unclear why classic objects, or those in our observable realm of existence, behave so radically different than the quantum building blocks that define them. To understand the transition between the two states, scientists must first bring an atom to a standstill, a task which we’ve yet to accomplish. A new atomic telescope may have resolved this challenge.

Theories about how this transition occurs do exist, but insofar no one has been able to test them because the necessary experiments cannot be accomplished without first achieving a complete standstill. A paper published in the Physical Review Letters journal demonstrates that these experiments may now be possible thanks to a special “atomic telescope.”

To appreciate the depth of what this research may have uncovered, it’s imperative that one first understand what it’s trying to accomplish. Slowing atoms to a standstill requires freezing them at unfathomable temperatures. As the temperature of an atom cloud gets cold enough, the wave-like nature of the individual atoms expands, and they eventually start behaving like quantum objects that stay together rather than diffuse. 

This in turn causes the atoms to attract or repel from one another rather than collide, speeding up their momentum and increasing the temperature of the atomic “cloud.” The wave nature of the atoms now begins to shrink (remember atoms behave like both particles and waves), causing them to behave more classically. Observing the expansion of this gas is what will provide the key insight into the transition between the quantum and classic state. 

So what’s new? Scientists proposed that the process used to create the coldest gas in the known universe, the Bose Einstein condensate (BEC), can be used together with magnetic lenses, in the shape of a telescope, to inhibit atoms’ sideways movement, while allowing the gas to expand downward. As a result, the limited horizontal movement of the atoms lowers their temperature into the nanoKelvin range.

How to cool to the nanoKelvin range?
Previously, there two techniques used in the quest to reach atomic standstill, both with their own limitations. The first, called “optical molasses,” requires using lasers to slow atoms down just as the same suggests. However, the slower the atoms move, the less efficient this technique becomes because the laser needs to be continuously adjusted to more precise tracking. The second technique, called evaporative cooling, separates atoms by temperature within a magnetic bowl and uses precisely channeled radio waves to selectively remove the hotter atoms. Eventually, as we wind up with fewer and fewer atoms, it becomes increasingly difficult to further cool the atoms as less and less atoms are left in the bowl. Neither of the two techniques permits the atoms to be cooled enough to break down the Heisenberg Uncertainty Principle.

Magnetic telescope
To cool the atoms into the picoKelvin (10-12K) range, the scientists proceeded with the evaporative cooling technique but then removed the magnetic bowl — once the atom’s temperature dipped into the nanoKelvin range — causing the atomic cloud to shoot upward through the vacuum and expand. Rather than allowing the expansion to freely occur, the researchers applied an additional magnetic field that resembles a lens (from the point of view of the atoms) in order to stop the cloud from expanding as it moves.

Atoms that pass segment of the lens closest to the outside perimeter experience a larger force caused by the magnetic field, causing their outward motion to be drastically slowed down, meanwhile the atoms breaching the center of the lens experience no force. After the atoms have finished passing through, the cloud begins to expand along the direction of its inertial movement, but the its sideway expansion is severely slowed down, creating a temperature different depending on the direction of motion. The atoms moving downward have a temperature of 2nK, where those in the transverse direction exhibit a temperature of 50pK, about 40 times less.

Like all lenses, the magnetic lens has a physical limit to how far it can focus the atoms, but if multiple lenses can be combined to form a “magnetic telescope” of sorts that compress the cloud while leaving the crosswise expansion very cold, it may allow scientists to control the rate at which the transition from quantum to classic occurs in order to explore a large variety of conditions.

Source: Ars Technica