Today's Super-Fast LED Lights Might Mean Tomorrow's Quantum Communication

Humans have been using light to communicate for a while now, whether it's reading CDs, sending laser-encoded data back from the International Space Station, or passing dots and dashes along semaphore proto-telegraph networks.

Naturally, we're always wanting to improve the state of the art to make light-based communication faster and able to carry more data. And the latest advance comes courtesy of a team of engineers based at Duke University. The Duke researchers, led by electrical engineering and physics professor Maiken Mikkelsen, have managed to develop fluorescent molecules that are 1,000 times faster than traditional LEDs. This is something that could revolutionize the way we communicate.

LED lightbulbs have already changed the way we light our world. So much so that this year's Nobel Prize for Physics was awarded to the three scientists who invented the blue LED lightbulb: Isamu Akasaki, Hiroshi Amano, and Shuji Nakamura. Red, green, and blue light together create the white light that illuminates our world, but isolating the blue spectrum was a major advancement. Blue uses far less energy than red or green light, leading to more energy-efficient and powerful light sources.

The relatively slow, non-directional emission rate of LED lights, however, has limited their use within high-speed communications.

The Duke team has successfully increased the photon emission rate of fluorescent molecules to a significant degree, taking the first step towards realizing the dream of having superfast LEDs for light-based communication systems.

Fluorescent molecules naturally give off light that they have absorbed in the form of electromagnetic radiation. And the molecules give off light in a fixed rate, at least until they're placed near an intensified light source. Proximity to a light excites the molecules and causes them to emit photons at a faster rate, an effect called Purcell enhancement.

Mikkelsen's team's experiment involved harnessed this Purcell effect. They created a plasmonic patch antenna from two silver nanocubes, which basically created a space that trapped the fluorescent molecules and excited them such that they increase the intensity of their light emission. The engineers also tried trapping the fluorescent molecules in a gap between one silver nanocube and a thin gold film.

This second set-up also saw the fluorescent molecules excited enough to move at a faster speed and emit more intense light. When the team tuned the gap's resonant frequency to match the frequency of the color of light that the molecules respond to, they saw an even greater increase in speed.

With everything perfectly calibrated to the fluorescent molecules' frequency, the team saw a thousand-fold increase in fluorescent speed.

The Duke researchers think they can do better. This experiment used randomly-aligned molecules. With more orderly molecules passing between the nanocube and the gold foil, they expect to see even more of an increase in speed.

This might be well and good in a laboratory as a proof-of-concept, but there are some interesting and immediate real-world applications. Faster fluorescence goes beyond more intense LED lights. Precisely placed molecules could lead to fast sources of single photons that would facilitate quantum cryptography.

Encrypted data can be hacked, making it vulnerable and an imperfect way of communicating. But quantum cryptography is an ultra-high speed and, in theory, totally unhackable way to transmit information. These superfast fluorescent molecules might just be the first step towards a world where we don't have to worry about who is handling our data where. We could, someday, live in a brighter and incredibly secure world.