Photons from their best side

Pairs of photons are the ideal carriers of entanglement and their polarization – one of several properties of the photon –  is commonly used to this end. While the polarization is easy to manipulate, it is as easily disturbed during transmission, which requires stabilization measures for every connection of a quantum network. On the other hand, particles of light also harbor entanglement in their energy and time domain, which are more robust during transmission, yet are harder to access and manipulate.

In a recent experiment published in Physical Review Applied, the best of both worlds is exploited. Physicists from the IQOQI Vienna use entanglement in the energy-time domain, which is easy to produce, for transmission and subsequently transfer the entanglement to the polarization domain of the same photons with high fidelity. The remotely produced polarization entanglement can then be conveniently used for quantum cryptography or interfaced with quantum processors. This enables robust quantum links and renders active polarization compensation obsolete, which is essential for low-maintenance and high-rate quantum networks.