Optical Tweezers

Definition

Optical tweezers are highly focused laser beams that can trap and move individual microscopic particles — including single atoms — using the physical forces light exerts on matter. Neutral atom quantum computers use arrays of optical tweezers to hold and reposition individual qubits.

In depth

Optical tweezers use a tightly focused laser beam to hold a tiny object in place. The light exerts a force on a small particle that pulls it toward the brightest point of the beam, so a single atom, molecule, or microscopic bead can be trapped at the focus. Arthur Ashkin developed the technique in the 1970s and 1980s and received a share of the 2018 Nobel Prize in Physics for it. In quantum computing, the objects are single neutral atoms, and each tweezer is a tiny trap with a depth of about a millikelvin and a width of about a micrometer.

Arrays of tweezers are made by splitting a laser with acousto-optic deflectors or spatial light modulators that shape the wavefront. A camera images which traps are occupied, because loading is random, with each trap filled about half the time. A real-time rearrangement step then moves atoms between traps to fill a target pattern without gaps, a method demonstrated by Endres and colleagues and by Barredo and colleagues in 2016. The result is a defect-free array of identical atoms at spacings of a few micrometers, in one, two, or three dimensions.

Tweezers also provide control during the computation. Moving tweezers can shuttle atoms to bring them close for entangling gates, and individually addressed beams can drive single-qubit gates. Arrays of thousands of tweezers have been built, with Caltech reporting an array of over 6,000 atoms in 2025, and groups continue to push the size, loading rate, and speed. Limits include laser power, which determines the number of traps, atom loss during imaging, and the time to rearrange large arrays.

Technical Definition

The technique relies on the dipole force, where a tightly focused laser beam creates an intensity gradient that attracts polarizable particles like atoms toward the beam's focal point, allowing precise three-dimensional positioning.

Visual Explanation: An Analogy

Think of optical tweezers like an extremely precise, invisible pair of chopsticks made of light, capable of picking up and placing individual atoms exactly where needed — a level of precision impossible with any physical tool.

Key facts

Where the idea comes from

Ashkin demonstrated optical trapping in 1970, and single-atom tweezers followed in 2001. Atom-by-atom assembly of arrays in 2016 turned them into quantum computing platforms.

Real-World Use Cases

• The core technology enabling neutral atom quantum computers like Pasqal's Fresnel processor
• Also used more broadly in biology and chemistry research for manipulating individual cells or molecules

How it differs from related ideas

• Optical tweezers trap neutral atoms with light, while Paul traps hold ions with electric fields.
• Optical lattices make regular arrays from interfering beams, while tweezers allow arbitrary patterns.
• Tweezers can move atoms during computation, which fixed lattices cannot.

Frequently asked questions

Related Terms

• Neutral Atom Qubit
• Rydberg State
• Quantum Simulator

Keep exploring

• Algorithm: Quantum Annealing
• Hardware: QuEra Aquila
• Hardware: Pasqal Fresnel (Orion generation)

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