How to use entanglement for long-distance or free-space quantum communication

Entanglement is exploited for applications in secure quantum communication over long distances and quantum cryptography protocols. Unfortunately, entangled particles are easily disturbed by their surroundings, and their entanglement is readily diminished by the slightest interaction with the environment.

An international team of physicists from Austria, Scotland, Canada, Finland and Germany have demonstrated how quantum entanglement can be strengthened to overcome particle loss or very high levels of noise. The researchers employed entanglement of systems with more than two levels, not the regular two-level qubits. By entangling particles of light through their spatial and temporal properties, scientists have now observed the survival of quantum entanglement under harsh environmental conditions for the first time. (

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