Copyright Nature Physics

It has been nine years since the first teleportation of a photon’s quantum state. Since then research in the area has flourished, driven by the quest to create a quantum computer that uses the photon state as a digital bit of information (a ‘qubit’). However, to be practical such computers are likely to require the teleportation of many qubits, and, until now, teleportation has been limited to just single-photon states. The problem is that the teleportation of each qubit requires an entangled pair of photons, which are notoriously hard to generate. Now, Qiang Zhang and his colleagues have improved the production of such pairs, and have succeeded, for the first time, in teleporting the polarization-entangled state of two photons1.

In essence, their technique is a scaled-up version of single-qubit teleportation. Rather than the sender and receiver sharing a single pair of entangled photons, they share two pairs. The work is made all the more impressive by the fact that the pair of photons that are teleported are also entangled: requiring three pairs in total. This important development has become possible owing to improvements in the creation and collection of entangled photons. By increasing the power of the pump laser used in parametric down conversion (the technique commonly used for generating polarization-entangled photons at ultraviolet wavelengths), and optimizing the optics capturing the resulting light, Zhang et al. have created a source that is almost five times brighter than in previous experiments. With a few more advancements like this, quantum computation may be just around the corner.