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You might finally be able to watch that 4k video without buffering, thanks to quantum mechanics and orbital angular momentum.

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Sources:
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https://physicstoday.scitation.org/doi/full/10.1063/1.1768672
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https://arstechnica.com/science/2020/05/corkscrew-light-promises-higher-optical-communication-data-rates/
https://science.sciencemag.org/content/368/6492/760
https://spectrum.ieee.org/tech-talk/semiconductors/optoelectronics/vortex-laser
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Image Sources:
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[♩intro].

Any time you watch a video like this one, a global network of electronics and cables comes together for one purpose: to send data from a server somewhere to you. And that requires a lot of data to move fast.

So, to send information around the world, we literally use the fastest thing in the universe: light. But there’s a problem: Even though light is fast, there’s only so much data we can physically store on a light beam. So if too many people try to access certain data at once, sites can slow down or crash.

And the problem is just getting worse as more and more devices go online. But scientists may have found a solution—and it literally comes with a twist. They discovered that by twisting light beams, they can store more information in them.

And as unreal as it sounds, this trick may be the key to our future internet. These days, most of the data the world produces is digital. And digital signals are basically just a string of two values called bits, which can either be one or zero.

So any information, whether it’s a YouTube video or an email thread, ultimately looks pretty similar in its most basic digital form: just a string of ones and zeroes. And we send that information around the world by encoding those bits into light that travels across continents and under the ocean through fiber-optic cables. But light can’t naturally store ones and zeroes—so to store data on a light beam, you have to manipulate the light wave in some way.

For example, digital radio stations transmit audio information by manipulating the frequency of light. They might use, say, high-frequency waves to encode a one and low-frequency waves to encode a zero.  But you could just as easily manipulate the intensity of light, which is represented by its amplitude, or height. In theory, high and low amplitudes could replace high and low frequencies to store the same information. 
You can do even better than that, though.

By using both the wave’s amplitude and frequency, you can double the rate that you transmit data, sending two bits at a time instead of one. Overall, the more distinct features of the wave you can change, the more bits you can encode onto it, and the more data you can send at once. But there’s one feature of light that we haven’t gotten control of yet—and it could be one of the most effective: orbital angular momentum.

Orbital angular momentum describes the movement of any whole object moving around a fixed point.  So, for instance, you have orbital angular momentum as you move around the Earth’s axis. The Earth has orbital angular momentum as it moves around the Sun.

And although it’s a little harder to wrap your head around, light waves can also carry this kind of momentum.  You can picture a light wave as a two-dimensional sheet of electric and magnetic fields traveling forward through space.  And that entire sheet can rotate around a fixed point as it travels, tracing a twisted, corkscrew-like pattern through space.  The thing is, even though lots of things have orbital angular momentum, light is a sort of special case… thanks to quantum mechanics. Since the properties of light are defined at subatomic scales, light has quantum mechanical properties.

And all you need to know about that is that it means light can’t just have any old amount of orbital angular momentum; it can only carry certain fixed amounts. And these fixed amounts are known as states.  Each state is a multiple of a fixed value called h-bar, a unit that physicists use to measure angular momentum at quantum scales. So a light beam might carry 1 h-bar, 2 h-bar, or 3 h-bar, and so on.

And, since the wavefront can rotate clockwise or  counterclockwise, the beams can actually have positive or negative values of those numbers. What’s useful about those states is that each one can be used to represent a piece of data!  And light beams with different amounts of orbital angular momentum don’t interfere with each other, so you can send them at the same time. That means, for each new state you add, you can hold more data.

And the number of states you can have is technically infinite. So, theoretically, this sounds promising. The trick is actually pulling it off.  In the past, scientists have managed to use special optical equipment to twist a light beam and give it a certain amount of orbital angular momentum.

The problem was, it took a completely different setup to create each state, so there was no way to send data quickly.  For that, scientists would need a single setup that could produce multiple different states on command. And finally, in a paper published in May of 2020, researchers at the University of Pennsylvania announced that they had done just that. They designed a special kind of laser that sent light into a tiny metal ring, just seven thousandths of a millimeter across.

As the light looped around inside the ring, it picked up some orbital angular momentum.  Then, it would scatter off little ridges inside the ring and shoot back out into the lab. As it left the ring, it carried the same orbital angular momentum it had while still inside. And what made this so successful was that, by controlling how much light they pumped into the ring clockwise or counterclockwise, researchers could create light beams with multiple different states—all from a single source!

Those same researchers even developed a special detector that could measure that momentum, meaning it could decode the information in those beams. These were both really exciting steps, and the fact that this idea has been carried out in some sort of practical way is really promising.  But there are still plenty of hurdles to go. For starters, the laser could only produce five of the potentially unlimited states that are physically possible.

It was also slower at transmitting data than existing electronics. But by refining this strategy, researchers think it may be possible to increase the amount of data we can send with light.  If it works, we could increase data transfer speeds many times over. And yes, you could finally stream Netflix in HD.

Thanks for watching this episode of SciShow! And in case twisting light isn’t enough for you, you can check out our video on how to stop light in its tracks—right after this. [♩outro].