Optical Tweezer Atom Rearrangement

Short answer: Neutral-atom quantum computers hold atoms in arrays of optical tweezers. Atoms load into the tweezers at random, so about half the sites are empty, and the atoms must be rearranged into a defect-free pattern before use. Papers from 2021 to 2025 report algorithms and hardware methods for this rearrangement, with laboratory results such as a 225-atom array and a per-cycle success probability of 0.996 for one method. These are experimental results from individual groups.

Why rearrangement is needed

A 2023 Physical Review Applied paper says defect-free atom arrays are a precursor for quantum information processing and quantum simulation with neutral atoms. They can be hard to realise at large scale because of losses when stochastically loaded atoms are rearranged into a target array. A 2025 arXiv paper (2501.01391) adds that rearrangement is also used in quantum computing to shuttle atoms between storage, interaction and imaging zones.

Moving tweezers

A 2021 Physical Review Research paper describes sorting stochastically loaded atoms with an auxiliary mobile tweezer as an efficient approach for intermediate-scale arrays in arbitrary geometries. The authors say the filling fraction of atom-by-atom assemblers is limited by redundant sorting moves and imperfect atom transport, especially at larger atom numbers. They propose a heuristic cluster algorithm that provides near-minimal moves, about one move per defect site to be filled, and experimentally demonstrate an array with a 98.4% filling fraction for one rearrangement cycle. By simulation they compare it with two other algorithms and say it suits large-scale assemblers. The paper notes that arrays had been scaled from one dimension to three, with array sizes of about 200 atoms.

The 2023 paper uses multiple mobile tweezers in parallel to sort and compress arrays in a way that avoids atom collisions. The authors say this reduces move complexity compared with single-tweezer and existing multitweezer algorithms, and that the best degree of parallelism balances algorithmic speedup against inhomogeneity between tweezers. They demonstrate a defect-free probability for a 225-atom array as high as 33% in a room-temperature setup after multiple rearrangement cycles. The algorithm can be used for any target geometry with an underlying periodic structure.

Rearranging with holograms

The 2025 paper takes a different route. It rearranges atoms by updating holograms on a fast spatial light modulator, interpolating the tweezer positions and optical phase between the start and end arrays, and computing new holograms every few milliseconds, limited by technology. The authors note that rearrangement is almost exclusively done with acousto-optic deflectors because of their fast response, but that sorting several rows at once needs multiple deflectors and limits the moves possible, and that handing atoms between static and mobile tweezers risks loss. They sort the same atomic sample into several geometries with a success probability of 0.996 per rearrangement cycle and describe the method as useful for large atom arrays.

What this does not tell you

The reported probabilities and fill fractions come from different setups, geometries and array sizes, so they should not be ranked against one another. These papers do not describe a complete computer, and defect-free loading is one step among many.

FAQ

Why are atoms rearranged?

Loading is random, so sites are empty until atoms are moved into a defect-free pattern.

How are atoms moved?

With mobile tweezers or by updating holograms on a spatial light modulator.

How large an array has been assembled?

One paper reports a 225-atom array with a defect-free probability up to 33% after multiple cycles.

Which method is best?

The papers use different setups, so the numbers are not directly comparable.

Is this a finished quantum computer?

No. It is a preparation step for neutral-atom experiments.