'Infinitely Fast' Light Speed Achieved in Nano Device

A nano-scale (billionths of a meter) device has been devised that permits light waves to flow ‘infinitely fast’ according to two collaborating teams of engineers.

In his theory of Special Relativity, Einstein established the speed of light constant (denoted by the letter ‘c‘ in his famous equation) that says that light moving in a vacuum (empty space) travels at constant speed — about 300 million meters per second. This limit is what makes things like “instantaneous (or simultaneous) communication” between two points impossible. Einstein famously referred to the quantum coherence “entanglement phenomenon as “spooky action at a distance.”

While there are a one or two known violations of this limit, the speed of light is considered the fundamental limit (on travel and communication speeds) and is the cornerstone of modern physics.

But this fundamental limit — at least in one very tiny dimension — has been broken thanks to physicist Albert Polman, at the FOM Institute for Atomic and Molecular Physics, Amsterdam, and Nader Engheta, an electrical engineer at the University of Pennsylvania.

The feat was achieved through designing a tunable nano “wave guide” that has a 0 (zero) “index of refraction”. When light waves interact with matter, some pass through with greater (faster) or lesser (slower) ease than others. For example, light moves slightly slower when passing through glass. Some materials, like certain metals, permit very little light to pass through them (these have a higher index). All materials have a refraction index number — usually greater than 1 — which is a measure of how optical light waves travel through them. To be precise, the refraction index is the ratio of light’s speed (in a vacuum) to its speed in a material.

Fairly recent experiments with meta materials has led to the development of materials with negative refraction indices. Such materials bend light in unusual ways and are what permits recent “cloaking device” breakthroughs.


infinitely fast light speed in nanodevice
Within the carefully sculpted waveguide, (left) light waves typically overlap to make a banded pattern (middle). However, depending on the width of the waveguide, waves of a certain wavelength travel infinitely fast, making the whole waveguide light up. Credit: AMOLF and University of Pennsylvania

But the engineering team figured out a way to “tune”  their device — composed of a 2000 nm long (and 85 nm wide) bar of silicon dioxide (glass) coated with a layer of conductive silver * — such that it has  a zero index of refraction.  When an optical beam of light is applied to the device, boundary conditions on the device cause the short wavelengths of light to bounce back and forth between the ends of the guide. As they do so, the “peaks and troughs” of the bouncing waves overlap, creating a pattern of light and dark bands (similar to the famous particle-wave duality experiments with light passing through two slits simultaneously). This is normal and expected.

Wavelengths above a certain threshold, or cut-off point,  do not flow along typical waveguides.

But in this new nano device, the team discovered something surprising: at the precisely that “cut off” wavelength, the entire waveguide bar lit up. Instead of interfering light waves, the waves suddenly began oscillating in synchrony and behaving as though they were everywhere at once. The team concluded that this has to mean that the peaks or phase fronts were moving infinitely fast.

Wile this fascinating discovery will not be over-turning Einstein any time soon, nor will it, according to most experts, permit instantaneous communication (but perhaps in quantum computing), but the engineers have plans for integrating these tunable nano waveguides into optical circuits which will allow for unprecedented real-time imaging and resolution.

Previously, other researchers have been able to slow light particle (photon) propagation using rhubidium atoms.

The experimental device was reported today in a paper (in press) at Physical Review Letters

Read more about this fascinating discovery at the Science Now news site.

* normally, light does not penetrate silver.

Top Image: (‘Relativity of Simultaneity’) ; Acdx  ; CC – By – SA 3.0 – Caption: Event B is simultaneous with A in the green reference frame, but it occurred before in the blue frame, and will occur later in the red frame.




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