Trapped-Ion Qubits

A trapped-ion qubit is a single charged atom held in a vacuum by electric fields. Lasers drive its gates. Two ions interact through the way the whole chain of ions wobbles together. Any pair in a chain can interact directly, and shown fidelities are the best of any platform. But the gates run roughly a thousand times slower than superconducting ones.

What is a trapped ion?

An ion is an atom that has lost (or gained) an electron. So it carries an electric charge. Charge is the handle we grab it by. Electric fields push on charged things. A carefully shaped electric field that flips back and forth very fast can hold an ion at one spot in space. Do this inside a chamber with almost all the air pumped out (a vacuum). Now the ion floats, touching nothing, cut off from almost everything that could disturb it.

The qubit is stored in two inner energy states of the ion. These are two set arrangements of its electrons and core. They are picked because they are extremely stable. Stored quantum information lasts for seconds or longer. A superconducting qubit keeps it for only tens to hundreds of microseconds.

There is one more contrast with printed qubits. Every ion of the same isotope (the same exact kind of atom) is truly identical. Physics guarantees it, not a factory. Compare two coins from the same mint, which differ a tiny bit, with two copies of the same digital song, which do not differ at all. So there is no qubit-to-qubit difference to tune away. But the lasers and electronics that control the ions still need careful, constant calibration (tuning) of their own.