## Quantum of computing

Another step to a possible quantum computer was reported in a news story in Nature:ubit

Ambitions to build a solid-state quantum computer received a boost this week from a team of researchers based at the University of Oxford, UK, who reported the simultaneous entanglement of 10 billion pairs of quantum bits, or qubits, in a highly purified crystal of silicon1.

Qubits are analogous to the bits used for programming in today’s computers, but are more useful because they can be placed in a ‘superposition’ of several quantum states at the same time. It has been shown theoretically that by running calculations in parallel, using many quantum states in superposition, a quantum computer could solve problems that would take a classical computer an infinite amount of time, for example, running Shor’s algorithm, which factors large numbers into primes and could be used, for example, to crack the most powerful encryption algorithms on the Internet.

Building a useful quantum computer will involve creating more than 1 million such qubits and entangling them together, so that the states of any one qubit are intrinsically linked with the states of others. The current record for the number of qubits all entangled together is 12.

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With her supervisor, John Morton, and other colleagues, [Stephanie] Simmons entangled the pairs of qubits by passing a sequence of radio and microwave pulses into a silicon crystal embedded with 10 billion phosphorus atoms and cooled to less than three degrees above absolute zero. The sequence of pulses flipped the magnetic orientation, or spin, of each phosphorus nucleus and one of its electrons until the pair became entangled with each other, forming a two-qubit system. Simmons and her colleagues confirmed the entangled state by detecting a microwave signal emitted from the crystal.

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Frank Wilhelm, who works on the theory of quantum-computing devices at the Institute for Quantum Computing in Waterloo, Canada, says that the work represents an advance over the more common method of qubit creation â€” the use of liquid nuclear magnetic resonance, which entangles the spins on molecules in fluids using a magnetic field.

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