Bristol University researchers, working in collaboration with colleagues from Japan, have managed to create an 'entanglement' filter so efficient that it can analyze two particles of light (called photons), and determine if they have the same polarization. If they do, they are allowed to go through, because that means the photons inhabit the same quantum state, although the operator of the device has no idea what that state is. In fact, in the case of most applications quantum physics has been involved in thus far, scientists have had little clue as to the state of the particles they were operating.

However, they have managed to conclude that its paramount for some applications that the photons be in the same state. So, they have created the current machine, which makes use of special types of light polarization-sensible mirrors and a special class of optical devices that enables stability at a nano level, of one billionth of a millimeter.

"This is a very exciting development in quantum information science. Because our entanglement filter acts on photonic qubits, it is promising for quantum technologies because photons are the logical choice for communication, metrology and lithography, and are a leading approach to information processing. The filter can be used for the creation as well as the purification of entanglement, which will be important in realizing quantum relays and repeaters for long-distance quantum communication," BU professor of Physics and Electrical Engineering Jeremy O'Brien, from the university's Center for Quantum Photonics, explains.

In the January 23rd issue of the journal Science, the researchers say that the new invention will have a large number of applications in quantum information processing as well, now that the challenges posed by building the device itself have been surpassed. The entanglement in quantum communications could now be deciphered or enciphered, opening the way for quantum encryption, a technique that is advertised to be unbreakable by third parties.