They will be the ultimate multitaskers – but quantum computers might take a bit of juggling to operate. Now, a team has simplified their inner workings.
Computers that take advantage of quantum laws allowing particles to exist in multiple states at the same time promise to run millions of calculations at once. One of the candidate technologies involves ion traps, which hold and manipulate charged particles, called ions, to encode information.
But to make a processor that works faster than a classical computer would require millions of such traps, each controlled with its own precisely aligned laser – making it extremely complicated.
Now, Winfried Hensinger at the University of Sussex in the UK and his colleagues have replaced the millions of lasers with some static magnets and a handful of electromagnetic fields. “Our invention has led to a radical simplification of the engineering required, which means we are now able to construct a large-scale device,” he says.
In their scheme, each ion is trapped by four permanent magnets, with a controllable voltage across the trap. The entire device is bathed in a set of tuned microwave and radio-frequency electromagnetic fields. Tweaking the voltage shifts the ions to a different position in the magnetic field, changing their state.
The researchers have already used this idea to build and operate a quantum logic gate, a building block of a processor. This particular gate involves entangling two ions – in other words, linking their quantum states such that they are fully dependent on each other. Hensinger says this is the most difficult kind of logic gate to build.
Manas Mukherjee at the National University of Singapore is impressed with the new technology. “It’s a promising development, with good potential for scaling up,” he says.
That’s exactly what the team is planning: they hope to have a trial device containing tens of ions ready within four years.
The fact that the device uses current technologies such as techniques for silicon-chip manufacturing means there are no known roadblocks to scaling up to create a useful quantum computer.
It won’t be plain sailing, though. Scaling up will mean creating magnetic fields that vary in strength over relatively short distances. This a significant engineering challenge, says Mukherjee. Then there’s the challenge of handling waste heat, which becomes more problematic as the processor gets bigger. “As with any architecture, you need low heating rates,” he says.
Journal reference: Physical Review Letters, DOI: 10.1103/PhysRevLett.117.220501
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