Quantum switch keeps photons tangled in fibre

Researchers at Northwestern University have built a switch that can route qubits, paving the way for quantum networking, and maybe one day (per Wired) a quantum internet.

The all-optical switch is capable of routing entangled photons along standard, telecom grade fibre-optic cables, without the entanglement breaking down. Because it uses existing technology, the breakthrough is potentially very useful.

One of the paper’s senior authors, Prem Kumar, said in a statement that his goal was to make “practical” quantum devices.

"We work in fibre optics so that as quantum communication matures it can easily be integrated into the existing telecommunication infrastructure. This switch opens new doors for many applications, including distributed quantum processing where nodes of small-scale quantum processors are connected via quantum communication links," he said.

The work is written up in Physical Review Letters where the researchers describe how they used pairs of polarization-entangled photons emitted into standard telecom-grade fibre.

From theuniversity’s announcement: “One photon of the pair was transmitted through the all-optical switch. Using single-photon detectors, the researchers found that the quantum state of the pair of photons was not disturbed; the encoded entanglement information was intact.”

Kumar concludes: "This switch opens new doors for many applications, including distributed quantum processing where nodes of small-scale quantum processors are connected via quantum communication links."