Transferring data using light passed along fiber optic cables has become increasingly common over the past decades, but each pulse currently contains millions of photons. That means that in principle, a portion of these could be intercepted without detection. Secure data is already encrypted, but if an eavesdropper was able to intercept the signals containing details of the code, in theory they could access and decode the rest of the message.
Single photon pulses offer total security, because any eavesdropping is immediately detected, but scientists have struggled to produce them rapidly enough to carry data at sufficient speeds to transfer high volumes of data.
A phenomenon called the Purcell Effect was used to produce the photons very rapidly. 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. This energy is then emitted in the form of a photon.
Placing the nanocrystal inside a very small cavity makes the laser light bounce around inside the walls. This speeds up the photon production by the Purcell Effect. One problem is that the photons carrying data information can easily become confused with the laser light. This issue was overcome by funneling the photons away from the cavity and inside the chip to separate the two different types of pulses. In this way, the photon emission rate is about 50 times faster than would be possible without using the Purcell Effect. Although this isn't the fastest photon light pulse yet developed, it has a crucial advantage because the photons produced are all identical — an essential quality for many quantum computing applications.
Each photon, or particle of light, represents a bit of binary code — the fundamental language of computing. These photons cannot be intercepted without disturbing them in a way that would alert the sender that something was amiss. Using photons to transmit data enables use of the fundamental laws of physics to guarantee security. It is 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.
This technology could be used within secure fiber optic telecom systems, although it would be most useful initially in environments where security is paramount, including governments and national security headquarters.