Unveiling the Invisibility Cloak

Long ago, it was reputed to be one of King Arthur’s most valuable possessions.

In the years since, its coveted magical abilities have slipped between the pages of several literary classics. A notable tyrant of the mountain in “Grimm’s Fairy Tales” tasted the enchantment; in an altogether different mountain, a young Bilbo Baggins stole the precious item from an obsessive cretin.

Most recently, it was Harry Potter who donned the prize.

Now scientists prove to be on the cutting edge of turning this age-old fiction into reality.

Zi Jing, lead author of the paper “An Ultra-Thin Invisibility Skin Cloak for Visible Light,” is working alongside a group of talented nanotechnology experts to render a working invisibility cloak.

BTR speaks with Jing about the development process and his hopes for this remarkable new technology.

BreakThru Radio (BTR): I’m curious, how did you first get involved in this particular line of study?

Zi Jing (ZJ): The invisibility cloak is something that has fascinated both myself and many others for quite some time. This is especially true for researchers working in the field of nanophotonics–which is the combination of nanotechnology and optics.

The problem up until recently was designing something that would be very thin, because these kinds of prototypes in the past were really big and hard to use. So our motivation in the beginning was to conceive a thin, thermal, and flexible design that would also function.

BTR: Speaking of past prototypes, how long has this currently been in development?

ZJ: It took us just about two years, from the very beginning of the idea up until the final realization of the device.

BTR: What have these stages of development looked like?

ZJ: Actually the conception itself was pretty straightforward. We discovered the right tool–which is a certain combination of nanostructures that function together to bend light. So the real difficulty wasn’t in finding the material we needed, but trying to figure out how to pattern those nanostructures in exactly the right position to help a three-dimensional object achieve cloaking effects. How would we create such a structure?

Those were the biggest hurdles, namely because they involve extremely sophisticated nanofabrication technologies. Most of the process took the shape of experimental realization, then back to calculation, and then more idea construction. The last feat, which was the fabrication pattern itself, was by far the most time-consuming.

BTR: This sophisticated nanotechnology you’re referring to utilizes gold nanoantennae, right?

ZJ: Yes, that’s correct.

BTR: Can you tell us a little bit more about these, and how you implemented them?

ZJ: Sure, so in this case the nanostructure is a kind of rectangular shape. In terms of size, we’re talking only 100 nanometers in length and 40 nanometers in width–so extremely small. Because of this, we have to pattern many of them together to achieve our effect.

Not only do we need a lot of them, but we also have to specifically design other shapes and sizes to arrange in a variety of positions until the cloaking effect can be pulled off convincingly.

BTR: So you’re basically playing nano-Tetris to cloak a three-dimensional object.

ZJ: [Laughs]. Yeah. And because a three-dimensional object casts a different height, or fall, each position or point on the object will need to have the proper corresponding nanodynamics to locally change the response of light.

BTR: I know we’re talking in terms of nano particles, but could you put this kind of scale in perspective for our readers?

ZJ: Sure. At the moment we’re working with these nanotype limitations, so we’re talking about an object the size of ten micrometers in width, and maybe ten micrometers in length. So it’s actually a little smaller than a single hair.

BTR: Woah.

ZJ: The key is that we have to first demonstrate the science behind it; we have to demonstrate the feasibility of cloaking on this level before we can move to different scales. Of course, we have to eventually scale up to macroscopic sizes.

BTR: So when you’re scaling to a much larger size than where it is now, do you foresee running into a lot of cost limitations? What’s the kind of ballpark so far as expenses go for this nanotechnology?

ZJ: Let’s just say that you can do it, but it would definitely cost a lot. Having said that, the advancements in this field have been really fast, exponentially in the past decade or so. Hopefully we’ll continue to do a good job in terms of advancing the science of invisibility cloaks, and we’re working with a researcher who is striving to improve the nanofabrication technology.

Also, utilizing some special techniques from others who have been printing the nanostructures very cheap can bring down the costs significantly. I would say that in ten years from now–when this nanofabrication technology catches up–it will be a lot easier and more practical to attain the cloaking science.

BTR: As we progress towards this foreseeable future, what kinds of practical applications are you imagining for the invisibility cloak?

ZJ: So obviously when you’re under the cloak, one of the first things that comes to mind is a military application. You could potentially cloak a jet fighter or an aircraft, and obviously your enemy won’t be able to detect it. This would definitely be a huge improvement for military strategy.

In a more general sense, for the public, one interesting example I can conjecture is a face mask of sorts. For instance, you could hide pimples, wrinkles, or rashes on your face, and cloak it to look smooth and nice. From the cosmetic point of view it could be something of great interest.

BTR: And this is something that could reach into all kinds of aesthetics, in ways that are only limited by our imaginations.

ZJ: It is. At its very essence, what we have here is the ability to make an object look like something else. Everyone always thinks about striving to render something to appear as if it weren’t there—to look like a flat mirror of sorts. But using this same kind of nanotechnology, these nanostructures and gold nanoantennae, you could also make an object like a pencil look like an eraser. You can achieve different optical illusions, which could factor into all kinds of display applications. Three-dimensional displays, for example. Even with a two-dimensional object you can achieve three-dimensional effects simply by reengineering the nanostructure.

BTR: With these seemingly limitless applications for optical illusions, are you worried that people might end up abusing this technology with more harmful intentions?

ZJ: Yeah, it’s a concept that a lot of scientists don’t really talk about with the invisibility cloak. Looking back though, many of the past scientific breakthroughs have scared people away at first. For an example, think of the laser. When it was first invented, people thought, “oh no, this is going to fry things!” Yeah, there’s always the potential for harm, but look at what we have now. Everyone uses laser pointers in their presentations, and the laser light has been an integral part of live performances.

We have to be both careful and open-minded about how we bring these innovations into existence.

Photo courtesy of Jukka Palmu.