05 September 2018

Researchers at Sheffield University utilised a phenomenon called the ‘Purcell Effect’ to produce light pulses very rapidly and transmit data that’s claimed to guarantee security.

Researchers at the University of Sheffield claim to have solved a key puzzle in quantum physics that could help to make data transfer totally secure.

Each pulse of light used to transfer data along fibre optic cables contains millions of photons which, according to the researchers, means that a portion of these could, in theory, be intercepted without detection.

It’s claimed the team has developed a way of generating very rapid single-photon light pulses. Each photon, or light particle, represents a bit of binary code, and cannot be intercepted without disturbing them in a way that would alert the sender that something was amiss. The researchers believe single photon pulses offer total security because any eavesdropping is immediately detected.

Up until now, scientists have struggled to produce photons rapidly enough to carry data at sufficient speeds to transfer high volumes of data. In a study published in Nature Nanotechnology, the Sheffield team describe how they utilised a phenomenon called the ‘Purcell Effect’ to produce the photons very rapidly.

They explain that a nanocrystal called a quantum dot is placed inside a cavity within a larger crystal – the semiconductor chip. The dot is then bombarded with light from a laser which makes it absorb energy, and this energy is then emitted in the form of a photon.

The scientists found that placing the nanocrystal inside a very small cavity made the laser light bounce around inside the walls. This speeds up the photon production by the Purcell Effect.

However, one problem this creates is that the photons carrying data information can easily become confused with the laser light.

The researchers overcame this by funnelling the photons away from the cavity and inside the chip to separate the two different types of pulse. In this way, the team says it succeeded in making the photon emission rate about 50 times faster than would be possible without using the Purcell Effect. 

They add that although this isn’t the fastest photon light pulse yet developed, it has a “crucial advantage” because the photons produced are all identical. This is said to be an essential quality for many quantum computing applications.

“Using photons to transmit data enables us to use the fundamental laws of physics to guarantee security,” says Mark Fox, professor of optical physics at the University of Sheffield. “It’s impossible to measure or ‘read’ the particle in any way without changing its properties. Interfering with it would therefore spoil the data and sound an alarm.”

According to Fox, the technology could be used within secure fibre optic telecoms systems, particularly in environments where security is paramount such as governments and national security headquarters.