Archie Lower Sixth Scholar You are warmly invited to our Senior School Open Morning Saturday 16 <strong>September</strong> <strong>2017</strong> 9.30am to noon (Entry at 13 and 16) HMC – Day, weekly and full boarding Boys and girls 13 to 18 To register please contact: admissions@bedes.org T 01323 843252 or online at bedes.org Bede’s Senior School Upper Dicker East Sussex BN27 3QH
ON THIS MONTH: BRITISH SCIENCE FESTIVAL Building a quantum computer ‘We’ve looked at a few football-pitch-sized areas’ “We don’t want to just beat IBM by 2 Qubits. ‘They have 15 right now so we’ve got to go to 17’, or something,” says Professor Winfried Hensinger. “That’s just boring. You’re never going to solve interesting problems like that.” Hensinger and his colleagues, at the University of Sussex’s Ion Quantum Technology Group, have much bigger ambitions. In February, they published what he calls “a construction plan - how to build a billion-Qubit quantum computer.” In a room on campus, behind two sets of security doors, they’re already working on a smaller prototype. And Hensinger has “talked to our VC, and we’ve looked at a few football-pitchsized areas” on which the real thing could be built. One major reason why building a quantum computer is “unbelievably hard”, Hensinger says, is that quantum states are fragile. Because “any interaction destroys quantum effects”, each Qubit – quantum bit – needs to be kept isolated from other atoms, etc. This can be done using superconducting circuits cooled to nearly absolute zero. However, to make a billion-Qubit quantum computer like that, you’d need a huge, impractical amount of cooling power. Instead Sussex’s preferred method is to trap charged atoms – ions – in a vacuum. Hensinger says that the University of Sussex were pioneers of the trapped-ion approach, and that, in their blueprint, they’ve introduced two other key innovations. The first relates to quantum logic gates. Previously, to make each gate, you needed two precisely focused lasers. Like the use of superconducting circuits, this isn’t practical at the scale they’re aspiring to. But Sussex have found a very engineering-efficient way to achieve the same effect – “by applying voltages to a microchip”. The second innovation is a way for different processors within the quantum computer to communicate with each other quickly. “The [previous] approach was to send information by an optical fibre, via photons. But that is unbelievably hard; people have been working for the last 10-15 years, and the maximum speed they’ve managed is seven per second: a very, very slow speed. Nowadays conventional computers work at gigahertz, and this works at hertz.” Sussex’s solution involves connecting the parts “using electrical fields”. “These innovations take away the fundamental barriers to building a large-scale quantum computer. And so we put all of these ingredients together, and wrote this blueprint paper, where we then calculated all the relevant quantities, like power dissipation. We gave construction diagrams of how to make the electrodes of the quantum computer, and so on, to show that it’s actually possible, not just to go to 50 Qubits, but to millions or billions… “We made sure that we included all the engineering details, so this is not just like the crazy vision of a madman, but it’s really based in solid engineering. That doesn’t make it easy. We’re not saying at all that this can be done in a year’s time, or something like that. It’s still a tremendous engineering [challenge].” Hensinger is clearly optimistic, though. When he tells me that Sussex will be building a large-scale quantum computer, he notably doesn’t say “maybe”. Steve Ramsey ‘Quantum leap: building the world’s fastest computer’ (a talk by Prof Hensinger), Tues 5th, 2.30pm, Sussex University campus. britishsciencefestival.org © Ion Quantum Technology Group, University of Sussex 43
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