Simone Colombo is developing a faster method for cooling gases with a host of quantum applications
Image by Gerd Altmann from Pixabay.
If you think about gaseous atoms, you probably picture them bouncing freely through space.
This constant motion is the natural state of atoms in the gas state. But when gases are cooled to or near absolute zero (-460 degrees Fahrenheit), they stop moving, entering what is known as the quantum degenerate state.
"When they are very cold, these atoms, they do not move anymore," Simone Colombo, assistant professor of physics, says. "And you need to treat them in a quantum way."
The "quantum way" involves a concept called wave-particle duality. This is when something - like an atom - sometimes behaves like a wave and sometimes like a particle. When it starts acting like waves, an atom's wavelength is inversely proportional to its velocity. This means that when an atom is still, when it is in the quantum degenerate state, it has a very long wavelength. This leads to the creation of a "super atom."
"You don't know exactly where the atom is," Colombo says. "The atoms start to behave in a collective way. So, you cannot distinguish every individual atom anymore. They all start behaving as a collective."
Quantum degenerate gases could be extremely useful in quantum sensors. Super atoms offer much more sensitivity in detecting electric, magnetic, and gravitational fields than regular atoms.
Researchers are developing quantum sensors that can measure gravitational acceleration with applications for studying geology and space travel, navigation in submarines or extremely remote places on land, as well as quantum computing. All of these applications could benefit from a better understanding and incorporation of quantum degenerate gases.
One of the issues with these gases, however, is that they can only be produced once and then destroyed. This poses an obstacle to conducting both lab and field studies which require rigorous repetition for accuracy.
Colombo has received $607,000 from the Department of Defense to develop a more efficient way to cool atoms down to get them into the quantum degenerate state.
"This is going to be quite useful to other lab experiments where you can start studying fundamental quantum mechanics at a very high repetition rate, or for field applications where you can measure much more frequently," Colombo says.
On a very basic level, to cool something down, you need to remove energy from it.
When it comes to quantum degenerate gases, the current cooling process starts with laser cooling. Scientists send light via a laser into the gas they want to cool. This method takes energy from the atoms in the gas and sends a higher-energy light back out, thus cooling the atoms.
However, laser cooling is rarely enough to get gases to the ultra-cold temperatures required to reach quantum degeneracy.
The next step is evaporative cooling. This process works in essentially the same way as letting a hot cup of coffee cool down before drinking. The steam that comes off the coffee is hot molecules leaving the beverage, thus lowering its average temperature.
"Evaporative cooling works the same way with atoms," Colombo says. "You remove hot atoms so that the sample becomes colder on average and at some point, you can reach a threshold where it is cold enough to reach the quantum degenerate gas [stage]."
This process takes between 10 and 20 seconds, depending on the type of atom. While this may not seem like a long time, when scientists need to do this process over and over again, it adds up.
Colombo is developing a new method that would take less than a second, reducing cooling time by a magnitude of 10 to 100.
Colombo is focusing on an isotope called Rubidium 85. He is focusing on this type of atom because it has special properties that will allow Colombo to use a magnetic field to eliminate interactions between atoms. By removing interactions between atoms, the gas can be cooled to quantum degeneracy with only laser cooling.
This will not only make the process faster, but more efficient. Without evaporative cooling, no atoms will need to leave the experimental trap.
"The impact is potentially huge," Colombo says. "Not only for industry, but also for research because it can speed up experiments and it can give insight into light-matter interaction in the quantum regime."
