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Today's Internet runs on linked silicon chips, but a future quantum version might be built from diamond crystals. Physicists report today in Nature1 that they have entangled information kept in pieces of diamond 3 metres apart, so that measuring the state of one quantum bit (qubit) instantly fixes the state of the other - a step necessary for exchanging quantum information over large distances.

Entanglement, which Albert Einstein called 'spooky action at a distance', is one of the weird phenomena that make quantum devices promising. A quantum Internet would use entangled photons travelling down fibre-optic cables to in turn entangle qubits, with the aim of one day providing super-secure communications, or delivering software and data to future quantum computers2.

The qubits themselves are analogous to the bits used in conventional computers, but can exist in a superposition of states, being both '0' and '1' at the same time (another aspect of quantum weirdness). Linked qubits could in theory zip through calculations that, on a classical computer, would take longer than the age of the Universe. Entangling them over a distance might allow unbreakable communication: for example, if the sender and the receiver of a message possess two sets of qubits that together provide an encryption key.

The technical feat of entangling qubits at a distance has already been achieved in other systems, including trapped ions and atoms. Although diamond is still playing catch-up, rapid progress has quickly elevated it to the A-list of candidates for quantum networks. “Connecting many qubits in diamond chips may be much easier than scaling up other systems,” says Ronald Hanson, a nanoscientist at Delft University of Technology in the Netherlands, who led the team that reported the results in Nature1.

Flawed diamonds
Qubits in diamond depend on imperfections in the materials' carbon lattice. When nitrogen atoms substitute for carbon atoms, and appear next to gaps, or vacancies, in the structure, a qubit can be created based on the spin state of electrons held in the gap. Their fluorescence gives a faint pink tinge to the crystal.

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