Published in Physics World, 1 Feb 2014
Leaked documents suggest that the US National Security Agency is developing quantum computers to crack cryptography codes, but what progress has the agency really made? Jon Cartwright investigates
The US National Security Agency (NSA) has a classified programme to build a quantum computer that can break modern Internet security, according to documents leaked by the former NSA contractor Edward Snowden. The documents, which were published last month in redacted form by the Washington Post, have surprised few physicists working in the field. However, they have led to speculation about the status of NSA research and a renewed debate on the risks of developing quantum computers.
Quantum computers are devices that rely on quantum phenomena such as superposition, in which a system exists in multiple states at once, and entanglement, in which the states of two systems become inextricably linked. Unlike classical computers, which store bits of information in definite values of 0 or 1, quantum computers store information in quantum bits, or qubits, which are a superposition of both. When qubits are entangled, any change in one immediately effects changes in the others. Qubits can therefore work in unison and solve certain complex problems much faster than their classical counterparts. […]
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