Cambridge, Massachusetts—Inside a cramped, windowless laboratory, mirrors, lenses, and beam splitters crowd together on a massive table, forming a dense and seemingly random thicket. In fact, each gizmo is precisely placed to control laser beams that ricochet through the setup before entering a port in a gleaming vacuum chamber jutting up through the table. Within the chamber, the beams suspend individual atoms of rubidium against gravity’s pull, arrange them in patterns, and manipulate their internal quantum states.
Dolev Bluvstein, a physicist at Harvard University, points to a digital camera mounted to peer down into the chamber. Several bright green dots shine on its screen. They are the atoms—hovering, fluorescing, making the atomic scale visible. They are also the quantum bits, or qubits, at the heart of a quantum computer, one that is pushing boundaries and rivaling more established concepts. Speaking over the thrum of pumps, Bluvstein says, “No matter what the advantages of different computational approaches, I think neutral atoms are the most fun because we take pictures of atoms.”
The effort at Harvard represents the leading edge in so-called neutral atom-based quantum computing. For decades, the approach languished as physicists struggled to coax even two atoms to interact, as they must to perform computations. Meanwhile, researchers pursuing other approaches raced ahead, assembling functional, albeit noisy, quantum computers with dozens of qubits consisting of tiny superconducting circuits or individual ions trapped on microchips.
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