Researchers at one of the world’s top scientific institutions, the Massachusetts Institute of Technology (MIT), have achieved a shocking breakthrough in quantum physics. They accomplished hours-long durations of continuous lasing with laser-cooled strontium atoms. Vera M. Schäfer, Zhijing Niu, and James K. Thompson follow with a really cool study. They have developed a unique approach for manipulating and probing quantum phenomena, centered around highly tunable, laser-cooled atomic gases. These findings have extremely important implications. More importantly, they could pave the way for discovering ultranarrow frequency linewidth lasers that can produce tremendous breakthroughs in the advancement of atomic clocks, dark matter detection and more.
In their experiment, the researchers chilled and decelerated strontium atoms in an ultra-cold gas housed in a vacuum chamber. The team stabilized the cooled atoms in a lattice arrangement inside a cavity. This configuration provided them with more control over the atoms’ behavior than ever before. This pioneering arrangement allowed the team to take advantage of recoil-driven lasing, producing sustained lasing that lasted for hours.
Understanding the Experimental Setup
The experimental journey started with the laser cooling of strontium atoms down to 10 millionths of a degree above absolute zero. This super-evaporative cooling, down to nanokelvin temperatures, is necessary to reach the exquisite control over these atomic gases that we desire. As per James K. Thompson, the Lasers Needful and this hazardous procedure is replacements need to be normal lasers repeatedly.
“To build this, we must continuously apply other normal lasers that cool the strontium atoms down to 10 millionths of a degree above absolute zero,” – James K. Thompson
To find out, the researchers made a pioneering move. Rather than use staggered approaches like most experiments of their kind, they repeatedly loaded and cooled the strontium atoms. Zhijing Niu, senior PhD student participating in the study, provided comment on this innovation that formed a foundation for the key.
“We have figured out how to laser cool and load our atoms continuously rather than staggered in time like almost all other experiments in our field do,” – Zhijing Niu
The continuous loading mechanism then allowed the researchers to create a highly stable environment surrounding those atoms. This stability worked against the random steps introduced by Brownian motion. Thompson explained this unexpected phenomenon, adding that it causes the pulse rate of the laser output to vary wildly.
“Yet when one builds these objects, one notices that it looks like these ‘bells’ are wiggling and jiggling around in frequency,” – James K. Thompson
The Achievements of Continuous Lasing
The principle innovation of this work is the successful demonstration of continuous recoil-driven lasing with laser cooled strontium atoms. Each time an atom absorbed a photon it would recoil. This would cause emission of an additional photon into the cavity, forming a positive feedback loop that kept lasing going for long stretches.
The researchers initially observed laser light emanating from their system while attempting to load the cold gas of strontium atoms. This surprising outcome compelled them to explore more deeply the mechanisms at work.
“We saw laser light coming out of our system when we were just trying to load a very cold gas of atoms between the highly reflective mirrors that form our laser cavity,” – James K. Thompson
When the team investigated the gain mechanism responsible for this lasing, they found that this gain mechanism was contributing heating effects in the system. This unexpected interaction produced a feedback loop which prevented significant shifts in the effective optical cavity frequency, regardless of our efforts to change the effective cavity frequency.
“However, this gain mechanism also causes atom-heating, which then causes a funny feedback loop that keeps the effective optical cavity frequency to a fixed value,” – James K. Thompson
Vera M. Schäfer, one of the postdocs on the work, pointed to an interesting lasing regime. It learned iteratively starting from a more chaotic regime and adjusting cavity parameters to arrive at a less stable regime.
“The most interesting lasing regime only appears when starting in a noisier state and then slowly changing the cavity parameters to a less stable regime that is only upheld by the continuous lasing,” – Vera M. Schäfer
Future Implications and Objectives
One of the focuses of this research is on creating ultranarrow frequency linewidth lasers. Realizing even a small fraction of this ambition would result in transformative discoveries throughout the basic and applied sciences. These lasers would greatly boost the precision of atomic clocks as well as broaden the ability to conduct dark matter searches.
James K. Thompson said that the results made possible exciting new explorations driven by this research.
“In the future, we plan to really use the narrow linewidth transition in strontium to build incredibly single-color lasers to explore the world,” – James K. Thompson
He mentioned ongoing research into protecting quantum sensors and simulating complex materials, such as BCS superconductors, using similar techniques.
“Along the way, we are already seeing lots of interesting things like protecting quantum sensors called matter waves and optical clocks against noise using collective effects or using these same systems to simulate BCS superconductors,” – James K. Thompson
These researchers are stretching the frontiers of understanding with their innovative research. They hope to apply their results to deepen our understanding of quantum mechanics and stimulate technological developments in adjacent areas.