43Ca+ qubit states and Raman transitions used for sideband cooling, single-qubit and two-qubit gates. Credit: arxiv.org/abs/1512.04600
The team achieved the logic gate, which places 2 atoms in a state of quantum entanglement and is the fundamental building block of quantum computing, with a precision (or fidelity) substantially greater than the previous world record. Quantum entanglement—a phenomenon described by Einstein as ‘spooky’ but which is at the heart of quantum technologies—occurs when 2 particles stay connected, such that an action on one affects the other, even when they are separated by great distances
The precision of the gate is a measure of how well quantum entanglement works: in our case, 99.9% precision means that, on average, 999 times out of 1,000 we will have generated the entangled state correctly, and 1 time out of 1,000 something went wrong. ‘To put this in context, quantum theory says that – as far as anyone has found so far – you simply can’t build a quantum computer at all if the precision drops below about 99%. At the 99.9% level you can build a quantum computer in theory, but in practice it could very difficult and thus enormously expensive. If, in the future, a precision of 99.99% can be attained, the prospects look a lot more favourable.’
Professor Lucas added: ‘A quantum logic gate on its own does not constitute a quantum computer, but you can’t build the computer without them.
‘An analogy from conventional computing hardware would be that we have finally worked out how to build a transistor with good enough performance to make logic circuits, but the technology for wiring thousands of those transistors together to build an electronic computer is still in its infancy.’
http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.117.060504 http://phys.org/news/2016-08-record-breaking-logic-gate-important-milestone.htmljCp
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