The race to build practical quantum computers might be entering a new phase. Some of the front-runner technologies are now facing size constraints, and others are rapidly coming up from behind.
For years, two leading approaches have enabled physicists to make progress partly by cramming devices with more and more qubits, the quantum equivalent of a computer's memory bits. One of those methods encodes qubits as currents running on superconducting loops. The other uses excited states of individual ions trapped in a vacuum by electromagnetic fields.
But in the past two years, qubits that consist of single neutral atoms — as opposed to ions — and are held with 'tweezers' made of laser light have suddenly become competitive. And other techniques that are at an even earlier stage of development could yet catch up.
"Superconducting qubits and trapped-ion qubits have done the most-advanced experiments, with the most qubits under control," says Barbara Terhal, a theoretical physicist at QuTech, a quantum-research institute at the Delft University of Technology in the Netherlands. "However, this is no guarantee that these platforms will stay in the lead."
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