neutral-atom array

A neutral-atom array stores each qubit in a single atom — often rubidium or cesium — held floating in vacuum by a tightly focused laser beam called an optical tweezer. A grid of hundreds or even thousands of these tweezers, made by splitting one laser into many spots, traps one atom per spot. Each atom is identical by nature, so unlike fabricated qubits there is no chip-to-chip variation: every qubit starts out the same. It is worth being clear up front that this is not a lithographic chip at all — there is no patterned silicon, just atoms hovering in light inside a vacuum chamber.

The qubit lives in two long-lived internal states of the atom, and gates are run with laser light. To make two atoms interact, they are briefly excited into a Rydberg state — a giant, puffed-up orbit that lets nearby atoms feel each other strongly. A standout feature is that the tweezers can be steered: atoms can be physically picked up and moved partway through a computation, so a pair that needs to interact is shuttled next to each other. That mid-circuit movement gives these machines flexible, reconfigurable connectivity rather than a fixed wiring graph etched into a substrate.

Honestly, every platform pays somewhere. Atoms occasionally get lost from their traps and must be reloaded, gates and readout are generally slower than in superconducting chips, and the optics that aim laser light at many atoms at once are intricate and hard to scale cleanly. But neutral atoms have pushed to some of the largest qubit counts of any platform, with no qubit modality having 'won' — they are included here mainly so the chip-based approaches can be compared fairly against a very different way of building a quantum processor.