Science has been chasing the mythical invisibility cloak for years, and recent experiments have even shown the concept to be valid. But what if you want to go beyond simply hiding something from the visible light spectrum? A new paper from the National Tsing-Hua University in Taiwan explores the idea of quantum cloaking. The researchers, Jeng Yi Lee and Ray-Kuang Lee, believe they have devised a method to take cloaks to the logical extreme with a quantum invisibility cloak. If it works, the quantum cloak could make it as if an object didn’t even exist.
The initial concept of a quantum invisibility cloak was born of the more traditional kind of invisibility cloak. Ordinary invisibility works on the basis of steering light waves around an object such that an observer cannot see it. This is called transformation optics, and the math backing quantum invisibility is startlingly similar. Transformation optics starts with Maxwell’s equations, which describe the behavior of electromagnetic radiation (like light) as it passes through space. Flipping this concept to the quantum realm requires a new starting point — the Schrödinger equation. Devised by Austrian physicist Erwin Schrödinger (of Schrödinger’s Cat fame), this is an equation that predicts the probability of an object being in a certain place at a certain time.
With light invisibility, scientists engineer materials that can distort a light field, but the quantum variety has to distort probability. According to the math, it should be possible to build a system where the probability of existing inside a region of space falls to zero. Of course, you could put something in that space and it would be cloaked from reality.
This isn’t a one-stop shop for all your reality-extinguishing needs, though. The paper points out a few weaknesses in the current hypothesis. Perhaps most importantly, the cloak can only shield an object from one aspect of the Schrödinger equation at a time. So the cloak could be used to protect a region of space from the quantum effects of nearby electrons, but other effects would still bleed through.
The cloak described in the new paper is basically an extremely complicated mathematical exercise. Jeng Yi and Ray-Kuang have shown that the there is a theoretical basis for the quantum invisibility cloak, but it doesn’t exist yet. They do posit one possible method for constructing it with a hollow silicon nanoparticle capable of shielding the interior from outside quantum effects.
The practical applications aren’t as fantastical as traditional invisibility, but could end up being considerably more important. The researchers believe that a properly implemented quantum invisibility cloak could be used to make quantum information storage and computing more feasible. Quantum invisibility is not a reality yet, but the groundwork has been laid. It only took a few years for transformation optics to go from theory to application. Maybe this new kind of invisibility will be on a similar trajectory.
Research paper: arXiv:1306.2120 – “Hide the interior region of core-shell nanoparticles with quantum invisible cloaks”