Filter Proposed for Quantum Network

Researchers at Hokkaido University in Sapporo, Japan, have developed a scheme for an optical filter involving linear optics and single-photon counters that would transmit photon pairs only if they share the same linear polarization. As reported in the April 8 issue of Physical Review Letters, the filter would be insensitive to the individual polarization of the photons, making it capable of preserving and creating entanglement between the photons.

The researchers predict that, if constructed, the filter could have applications in quantum information networks such as quantum nondemolition measurements of entanglement and generation of multiphoton quantum codes.

The roadblock to constructing such a device is the development of a detector that can maintain quantum efficiencies that are high enough to distinguish single-photon events from two-photon events at nominal operating temperatures.