Placeholder Image

Subtitles section Play video

  • Light has been a favorite subject of study since

  • pretty much forever and it still has more amazing hidden properties waiting to be discovered.

  • Recently researchers found that under the right conditions, light can behave like a liquid with particles that flow in unison.

  • That’s rightliquid light. Well, that’s not quite right.

  • Liquidis a useful analogybut it implies the light is in a liquid state,

  • when really it’s in a more exotic state of matter, namely a Bose-Einstein condensate, or BEC.

  • Sometimes called the 5th state of matter after solids, liquids, gases, and plasma,

  • a BEC is created when a group of particles acts as one giant superparticle.

  • This can be done using entire atoms like rubidium and potassium cooled to near absolute zero.

  • Like photons, atoms behave like both waves and particles,

  • and as they cool to extreme temperatures they lose momentum and their wavelengths blur together.

  • Pioneering Indian physicist Satyendra Nath Bose and Albert Einstein predicted they could exist nearly a century ago.

  • Because they require such low temperatures, Einstein thought it would be impossible to actually observe one.

  • Turns out the impossible became possible in 1995, when the first Bose-Einstein condensate was created using roughly 2,000 rubidium atoms.

  • A different technique for creating Bose-Einstein condensates out of light was discovered in 2010,

  • and interestingly, it involves much more reasonable temperatures.

  • When cooled, photons have a tendency to vanish into the walls of whatever is containing them.

  • It’s sort of hard to make several particles behave in concert when they keep running off and hiding

  • so the key is to keep the photons bouncing back and forth off of two curved mirrors placed just over a micrometer apart.

  • In between the mirrors is a liquid dye that repeatedly absorbs and re-emits the photons, cooling them to room temperature in the process.

  • The mirrors aren’t perfect so some photons still get lost,

  • but by keeping their numbers topped up with more photons from a laser, a Bose-Einstein condensate can be created and maintained.

  • The same team that cracked this process is still tinkering with manipulating light,

  • and in April of 2021 announced they had observed a phase change in a BEC,

  • meaning theyve seen two distinct phases of this exotic state of matter.

  • Then in October, another research team announced they had created light that acted like a liquid and demonstrated what they calledsocial behavior.”

  • The scientists sent their cooled photons through a structure known as a Mach-Zehnder interferometer.

  • The interferometer splits into two paths that then rejoin and split again.

  • A photon can travel down both paths simultaneously,

  • but one path can be heated to change its length

  • and make it so the photons are out of sync when they meet up again, creating an interference pattern.

  • The researchers experimented with multiple interferometers that either had both exit paths open, both closed, or one open and one closed.

  • Interestingly with that last interferometer, the photons seemed todecidewhich path to take.

  • They went down the closed path, which the researchers postulated was a way for more of the condensate photons to stick together.

  • This is why they called itsocial behavior.”

  • Research like these two recent studies is useful for studying properties of Bose-Einstein condensates.

  • What scientists learn may also one day play a part in the encryption of quantum communications.

  • Even if these studies have no immediate application, it’s nice to know that light still has plenty of surprises for us in store.

  • If you liked this episode on liquid light, you might also like this one about how scientists discovered liquid glass.

  • Make sure to hit that subscribe button and keep coming back to Seeker for the latest news on new phases of light and matter and all that good stuff.

  • Thanks for watching and I’ll see you next time.

Light has been a favorite subject of study since

Subtitles and vocabulary

Click the word to look it up Click the word to find further inforamtion about it