@D Hamilton
This clip from your article explains the difference between neutral atom and trapped ion QC. Neutral atoms don’t repel each other, trapped ions do. So for Rydberg state driven neutral atom entanglement, there is a control issue requiring a different method than in trapped ions which must be kept in the array using magnetic fields using microwaves driving the train if using Ytterbium ions and UV lasers, or magnetic fields driving the train if using Barium ions and green (visible) lasers. The repelling ions limit the number of total ions controlled in a given array, unlike the neutral atoms that can be packed in counts of millions. Fidelity and qubit counts may be different between these two gate-based QC approaches even if neutral atom shows higher qubit coherence times and counts.
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Neutral atoms in low-energy states interact weakly with each other and thus can be packed into compact arrays. Proponents see that as a key advantage of neutral-atom quantum computing relative to more mature approaches that use ions trapped in electric fields or superconducting circuits at millikelvin temperatures. Scaling up quantum computers from hundreds of qubits to millions is a challenge for all proposed architectures, but space is not an issue for neutral atoms; a millimeter-scale array could hold as many as a million qubits.
To turn on interactions between qubits, researchers target a pair of adjacent atoms with a laser pulse that excites one of them to a high-energy state called a Rydberg state, in which a valence electron orbits far from the nucleus. The Rydberg atom’s strong electric dipole interactions prevent the laser from also exciting its neighbor, an effect known as a Rydberg blockade, but it’s impossible to know which of the atoms was excited. The result is a single excitation shared between two qubits that can’t be described separately—the characteristic feature of entanglement, the key phenomenon that allows quantum computers to outperform their classical counterparts. Rydberg entanglement fidelity has improved markedly in the past five years but still lags behind that of trapped ions and superconducting qubits.
Entangled neutral atoms.