New ‘twisted’ laser beam can shape ultracold atoms into unusual shapes

(ORDO NEWS) — Getting atoms to do what you want isn’t easy, but it’s at the heart of a lot of groundbreaking research in physics.

Creating and controlling the behavior of new forms of matter is of particular interest and an active area of ​​research.

Ultracold atoms, cooled to temperatures close to absolute zero (-273°C), are of great interest to researchers, as they allow us to see and study physical phenomena that would otherwise be impossible.

At these temperatures, colder than outer space, groups of atoms form a new state of matter (not solid, liquid, or gaseous) known as a Bose-Einstein condensate (BEC). In 2001, physicists were awarded the Nobel Prize for creating such a condensate.

The defining feature of a BEC is that its atoms behave quite differently than we would normally expect. Instead of acting as independent particles, they all have the same (very low) energy and coordinate with each other.

It’s like the difference between photons (particles of light) coming from the Sun, which can have many different wavelengths (energies) and oscillate independently of each other, while laser beams have the same wavelength and oscillate together.

In this new state of matter, the atoms act much more like a single, undulating structure than a group of individual particles.

The researchers were able to demonstrate undulating interference patterns between two different BECs and even create moving “BEC blobs”. The latter can be regarded as the atomic equivalent of a laser beam.

Drop movement

In our latest study, carried out with our colleagues Gordon Robb and Gian-Luca Oppo, we explored how specially shaped laser beams can be used to manipulate ultracold BEC atoms.

The idea of ​​using light to move objects is not new: when light hits an object, it can exert (very little) force. This radiation pressure is at the heart of the idea of ​​solar sails, in which the force exerted by sunlight on large mirrors can be used to propel a spacecraft through space.

However, in this study, we used a special type of light that can not only “push” atoms, but also rotate them, something like an “optical wrench.”

These laser beams look like bright rings (or doughnuts) rather than spots. and they have a swirling (helical) wavefront, as shown in the image below.

New twisted laser beam can shape ultracold atoms into unusual shapes
Light with orbital angular momentum (OAM, m) “twirls” as it moves

Under the right conditions, when such curved light is directed at a moving BEC, the atoms in it are first attracted to the bright ring and then rotate around it. .

As the atoms rotate, both light and atoms begin to form droplets that rotate around the original direction of the laser beam, and then are thrown outward, outside the ring.

The number of droplets is equal to twice the number of light swirls. By changing the number or direction of swirls in the initial laser beam, we had complete control over the number of droplets formed, as well as the speed and direction of their subsequent rotation (see image below).

Twisted light hits the moving BEC, forming a ring out of it, and then breaking it into several BEC droplets that rotate around the direction of the light before breaking free and twisting. (Grant Henderson and Allison Yao).

We could even prevent the atomic droplets from flying out of the ring so that they continue to orbit much longer, creating a form of supercold atomic current.

Ultracold atomic currents

This approach to the passage of curved light through ultracold atoms opens up a new and simple way to control and shape matter into unconventional and complex shapes.

One of the most exciting potential applications of BEC is the creation of “atomtronic circuits”, in which the material waves of ultracold atoms are guided and manipulated by optical and/or magnetic fields to form advanced equivalents of electronic circuits and devices such as transistors and diodes. /p>

The ability to reliably manipulate the shape of a BEC will eventually help create atomic-electronic circuits.

Our supercold atoms, acting as an “atomic superconducting quantum interference device” here, have the potential to provide a distant future. superb devices that n conventional electronics.

This is because neutral atoms cause less information loss than electrons, which normally make up the current. We also have the possibility to change the characteristics of the device more easily.

Most exciting, however, is the fact that our method allows us to produce complex atomic-electronic circuits that would simply be impossible to design with conventional materials.

This could help develop well-controlled and easily reconfigurable quantum sensors capable of measuring tiny magnetic fields that would otherwise be immeasurable.

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