Photonics circuit shown to handle quantum information

The team showed that a multimode interference device (MMI) — a basic photonic circuit frequently used in classical optics — can be adapted to handle quantum information.

‘We can ride on the back of the existing telecommunications industry through the fibres that are already in the ground. The photonic devices we are using are pretty well established. What we’re doing is reconfiguring them and making them work in a quantum regime,’ said Prof Jeremy O’Brien of Bristol University.

Quantum computing has been muted for some time now. It exploits the notion that a unit of information can represent both a one and a zero state simultaneously. The potential power of quantum computing comes from the possibility of performing a mathematical operation on both states simultaneously.

While O’Brien believes that a full-scale quantum computer is at least several decades away, the underlying technology has tangible applications in the medium term in things such as secure communications and metrology — the ability to model chemical and energy reactions with supreme precision.

‘We’re half in an engineering faculty and half in a physics department, so we’re all about taking these ideas in quantum physics and turning them into practical technologies that you can take into the real world,’ said O’Brien.

In fact, there are a handful of companies now augmenting their communications with quantum encryption. The technique was used in the most recent Swiss Federal Elections to communicate between polling stations and head office. These companies do not make this known, however, as they don’t want to alert people to the sensitivity of their information.

O’Brien said there were several advantages to using photonics as opposed to other technologies currently being investigated in quantum communications.

‘Photons are unique in their low-noise properties,’ he added. ’The use of an electron’s spin or the state of an atom are alternatives and other groups are pursuing these, but they are typically more susceptible to noise. With a photon, you can put it in a horizontal polarisation and send it to the moon and back and it’s still horizontally polarised.’

Since the MMI built in the current project essentially represents a basic building block of circuitry, the team is now looking at how to scale up the technology to create complex quantum networks with greater power.