It turns out that what goes up doesn’t have to go down.
Physicists have achieved a phenomenon known as subradiance. atom It stays in an excited state for the first time in a dense cloud of atoms.
Physicists have reported in a new study that subradiance could allow scientists to create reliable, long-lived quantum networks from atomic clouds.
Atoms acquire energy by absorbing photons (light particles) that jump electrons from the lowest-energy “ground” state to the higher-energy excited state. When excited, the atom naturally emits photons and returns to the ground state. However, this is not always the case. When many atoms are packed together and separated at a distance shorter than the wavelength of the emitted photons, the light they emit cancels itself and the atoms remain excited.
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This process, called subradiance, effectively prevents the collapse of large groups of excited atoms, or “ensembles.” Subradiance was previously observed in dilute atomic populations and ordered atomic arrangements, but has never been observed in dense cloud clouds.
Subradiance works for a phenomenon called destructive interference. When two waves of light of the same amplitude occupy the same part of space, the peaks and valleys of the waves are aligned and constructively added, doubling the brightness or destructively combined waves. Is created and both are offset. Completely waves.
But how can we keep those atoms excited by canceling the light emitted by the cloud of atoms?According to researchers, the key to understanding this idea is to observe subradiance. Quantum mechanics — Strange and stochastic rules governing the elementary particle domain.
On the small scale of the strange quantum world, both particles have wave-like properties and can travel all infinite paths between one point and another at the same time. The path that particles “select” and the path we observe depends on how the wavy particles interfere. Trapping the atom in the excited state is not a destructive interference between the emitted photons, but instead it can occur, preventing the photons from being emitted first.
“To understand the probability of a physical event, we need to sum up all the paths leading up to that event,” co-author Loïc Henriet, a quantum software engineer at French quantum processor company Pasqal, told Live Science. I told you by email. “In some cases, the paths constructively interfere to promote the phenomenon, and in other cases, there is a destructive interference effect that suppresses the probability. Due to the destructive interference of photons that should have been emitted from individual atoms. Excited state decay is collectively prevented. It is shared by atomic ensembles. “
The team trapped a chaotic cold cloud to induce subradiance in high-density gas for the first time. rubidium Atoms in optical tweezers traps. The technology, which scientists won the Nobel Prize in Physics in 2018, uses a high-concentration laser beam to keep small particles in place. The rubidium atom was then excited by the second burst of laser light.
Many of the excited atoms decayed rapidly through a process called superradiance associated with subradiance, but instead have atoms that constructively combine the emitted light into a super-powerful flash. .. However, some atoms remain subradiant or “dark” and unable to emit destructively interfering light. Over time, some atoms in the superradiant state also became sub-radiated, and the mushroom cloud became more and more sub-radiated.
“We just waited for the system to collapse into dark state on its own,” Henriette said. “The dynamics of decay are fairly complex, but we know that interactions allow the system to generate sub-radiative states over a longer period of time.”
Once the researchers found a way to create a subradiant cloud, they adjusted the optical tweezers to rock the atom out of dark state so that it could emit light without destructive interference. As a result, the light from the clouds exploded.
The team also created multiple clouds of various shapes and sizes to study their properties. Only the number of atoms in the excited cloud affected its lifetime — the more atoms, the longer it took them to return to the ground state.
“The interference effect is a collective effect. It takes some emitters for it to happen,” Henriette said. “And if you increase the number of emitters, it becomes more noticeable. If you have only two atoms, it is possible to have some kind of subradiance, but the physical effect is very small. It can be suppressed by increasing the number. Photon emission more effectively. “
Now that researchers can create and control subradiant mushroom clouds, they plan to study techniques such as arranging clouds in regular geometric patterns. This allows you to precisely adjust the amount of interference required, making it even easier to control. Life of excited atoms.
Researchers believe their findings will help develop many new technologies, including new quantum computers and more accurate weather forecast sensors.
Researchers published their findings in the journal on May 10 Physical Review X..
Originally published in Live Science.
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