Can we use light to store information?

Chris Smith asked material scientist Rachel Oliver, from Cambridge University, to light up an answer for Helen on Facebook. 

Rachel - That’s a really cool question. Storing information with light is actually quite hard because storing light; keeping it kind of stable in one place is difficult. But transmitting information with light is something we do all the time. You can take this back a really long time, so I guess, even in ancient times people used fire to send signals. And certainly in Elizabethan times, there were these beacons set up all round the country which were there to be lit if they saw an invading armada coming from Spain. Eventually they did and they lit their beacons and warned London and Dover of what was happening and what they needed to do.

In the modern world: you hear adverts on the telly for superfast fibre optic broadband. That’s a slightly more sophisticated way but it’s basically sending pulses of light down long thin pieces of glass to send information about the internet.

There’s the question: how small can we go with light? How little light can we use? We talked before a little bit atoms as the smallest piece of a material you can have. The smallest piece of light you can have is something called a photon: it’s what we call a fundamental particle of light and it’s a really amazing thing. We can actually do experiments which show that light is a stream of particles and, at the same time, light is also a wave which sounds completely contradictory, and we can transmit, store, or move information on a single photon. Interestingly, you can think of photons not just as being particles, but a point in a specific direction; that’s the property of the light called its polarisation. For example, a light putting up is a one light pointing sideways as a zero would work and then you can transfer information like that on a single photon. The tiniest possible particle of light.

Chris - In essence, this is how we’re transmitting data at terabit rates all over the world now and fibre optics for the internet isn’t it? That’s how programmes like this are streaming all over the world at the moment?

Rachel - Yeah. We’re not using single photons yet. We’re using pulses with lots of photons in. That’s partly because when it goes down the fibres, quite a lot of the light gets absorbed into the glass, so if we only send it on single photons, we would lose out. But there are schemes for using single particles of light to transfer information perfectly securely so you can use it then to basically keep really really valuable information very very safe. There’s even then schemes for how you deal with the fact that you lose large chunks of photons down your fibre that gets absorbed into the material.