Continuous lasage of several hours reached using laser cooled strontium atoms

Laser cooled atomic gases, cooled atom gases at temperatures around absolute zero using laser technologies, have proven to be versatile physical platforms to study and control quantum phenomena. When these atomic gases interact with light within an optical cavity (i.e. a structure designed to trap and improve light), they can give birth to effects that can be used to carry out quantum detection or simulate complex quantum systems.

Using atomic gases loaded in optical cavities, physicists observed various intriguing effects, including self-organization phase transitions, characterized by the spontaneous arrangement of gas atoms in ordered diagrams, lasage and preservation of quantum coherence. Generally, however, these effects are only observed for short time, as new atoms must be recharged in the cavity so that they are again produced.

Researchers from Jila, a joint research institute at the Colorado-Boulder University and the National Institute of Standards and Technology, recently demonstrated a continuous bad that lasted hours using the strontium-88, cooled by laser (⁸⁸Sr) atoms loaded in a cyclical optical cavity (that is to say circular). Their article, published in Nature physicscould open new possibilities for the development of ultra-Indian lasers, as well as quantum computers and detection technologies.

“The original objective of our experience is to build a continuous superradiant laser, a tool that would allow us to make high precision frequency measures to short time scales,” said Dr. Vera Mr. Schäfer, first author of the newspaper, to Phys.org. “This could help us explore different diets to seek dark matter and other physical news.”

The long -term objective of researchers Schäfer, Niu, Thompson and their colleagues is to make lasers of extremely advanced and ultranarrow frequency width, which could be used to search for black matter or to develop sophisticated devices, such as atomic clocks. While working towards this objective, however, they discovered a curious and unexpected effect, which reflects the fact that nature can organize spontaneously when the energy is pumped into a system.

“We have seen the laser light get out of our system when we just try to load a very cold atoms between the very reflective mirrors that form our laser cavity,” said Professor James K. Thompson. “To be clear, our laser cavity is like a bell but for light instead of sound. It likes to ring at a specific frequency.

“The atoms made this” bell “ring and gave off the light. When we studied where this light came from, we found a lot of strange behaviors, among them which modify the frequency of resonance of the bell barely changed the frequency of the light it emitted.”

After their unexpected observations, the researchers decided to better understand the underlying physics. This could, in turn, inform the future development of atomic clocks and gravitational waves.

“To understand this, I have to tell you a story about atomic clocks and gravitational waves,” said Thompson. “It turns out that detectors of atomic waves and gravitational waves are counting on types of optical cavities with stable frequencies very, very, very (I said very very?).

“However, when we build these objects, we notice that it looks like these” bells “wiggles and trembles in frequency. Why? Because they are made of real atoms at finished temperatures which undergo the equivalent of random trembling around the Brownian movement.”

To get around this limitation of atomic clocks and gravitational waves, Thompson and his Jila laboratory are trying to build a superradiant laser. The frequency of this laser should not depend on the frequency of the optical cavity but, rather, on an atomic transition of very narrow frequency in the strontium atom.

“To build this, we must continually apply other normal lasers that cool the atoms of Strontium to 10 million degrees above absolute zero,” said Thompson.

The senior doctoral student Zhijing Niu added: “We understood how the laser cools and load our atoms continuously rather than shifted in time like almost all the other experiences of our field do it (that is to say cool and load atoms, briefly make a science, throw them away.”). “

Before even taking advantage of the very narrow atomic transition during their experiences, the researchers observed that laser light came out of the optical cavity and found that it persisted for hours. This fascinating observation was key inspiration behind their recent work, because they wanted to understand its underlying reasons.

“It was a fairly special experience because normally you try to achieve a specific goal and solve problems along the way,” said Schäfer. “We saw something completely unexpected and we initially had no idea what caused it. So we excluded different possibilities step by step until we finally started to understand what was going on and discovered that without us even trying, this lasing mechanism stabilizes the effective frequency of our cavity.”

In the end, the researchers realized that the laser they observed results from the absorption of a photon and a subsequent stimulated emission, producing a different moment. In other words, they found that ⁸⁸The SR atoms caught a photon, making it go back and throw a photon in the cavity, producing the continuous laser they observed.

“This seems to be the gain mechanism provided by nature when we put energy in the system via our laser cooling beams,” said Niu.

“However, this gain mechanism also causes the atoms heating, which then causes a funny feedback loop that maintains the effective frequency of the optical cavity to a fixed value, even when we tried our greatest to change it,” added Thompson.

The recent study carried out by this research group offers new information on light interactions, which could shed light on the future development of superradial lasers. In particular, a large part of the physics they observed only occurs continuous, as opposed to cyclical experiences.

“The most interesting lasing diet only appears when you start in a more noisy state, then slowly changing the cavity parameters into a less stable diet which is only maintained by continuous lasing,” said Schäfer. “Thus, the construction of a continuous cold atoms experience allowed us to see new effects.”

Inspired by recent work in the field, including this recent study, many researchers interested in atomic physics and laser now pay their attention from cyclical experiences to continuous experiences. The resulting continuous operating platforms could open the way to the introduction of high-performance new technologies, including quantum computer systems and Linewidth Ultranarrow lasers.

“In the future, we are really planning to use Linewidth’s close transition from strontium to build incredibly monore lasers to explore the world,” added Thompson. “Along the way, we already see a lot of interesting things such as the protection of quantum sensors called waves of material and optical clocks against noise by using collective effects or using these same systems to simulate BCS superconductors. We will certainly remain very busy!”

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