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The Sciences

Harnessing Quantum Weirdness to Make Spy-Proof Email

80beatsBy Eliza StricklandAugust 28, 2008 7:14 PM

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It may not be a big market, but it's presumably a lucrative one: To meet the needs of consumers who are in the business of transmitting classified national secrets, physicists are working on an absolutely secure communication system that uses the strange laws of quantum mechanics to encode information. The latest experiments in this field, called quantum cryptography, produced a system that researchers say would theoretically work to transmit information around the globe. The system relies on a concept known as quantum entanglement to establish hack-proof communication.

Entanglement allows two particles to be quantum-mechanically connected even when they are physically separated. Although the specific condition of either particle cannot be precisely known, taking measurements of one will instantly tell you something about the other. The trick can't be used to actually send information, because each particle's condition is random until it is measured. But entanglement can be used for encrypting data if a sender and a receiver make measurements on a number of entangled particles and then compare their results [Nature News].

After performing the measurements, they use their data to generate a quantum mechanical 'key' that can be used to share top-secret information. Any eavesdropper will disrupt the entanglement, ruining the key and causing the sender and receiver to break off their communication

[Nature News]

. These entangled particles are usually photons which are transmitted via fiber optic cables. Previously, attempts at quantum communication over distances of more than 60 miles have failed, because the photons that are sent through fiber optic cables eventually get disrupted. But in a new study, published in the journal Nature [subscription required], researchers describe a way to overcome this problem. The researchers

developed a robust "quantum repeater node" that could, if developed further, send high fidelity signals over segments that, when linked to similar nodes, can form the building blocks of a quantum communication network to span the world [Telegraph].

Quantum communication is beginning to be used beyond the lab:

Image: iStockphoto Related Post: Entangled Particles Seem to Communicate Instantly--and Befuddle Scientists

Last fall, a secure QC line built by Geneva-based Id Quantique was used to transmit voting data in the Swiss national elections. And New York–based MagiQ Technologies has sold "a moderate number" of systems to clients in military and intelligence agencies, financial institutions and telecom companies [Popular Mechanics].

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