Ion-Trap Gate Hardware
Trapped-ion processors hold atomic ions in electromagnetic traps and manipulate them with lasers or microwaves, using shared motion to entangle qubits.
Trapping the Qubits
A trapped-ion quantum computer confines individual atomic ions, commonly ytterbium, calcium, or barium, in the oscillating fields of a radio-frequency Paul trap. Each ion is a nearly identical natural qubit, with information stored in two long-lived internal electronic states, either a hyperfine pair separated by microwave frequencies or an optical pair separated by an optical transition. Because the qubits are real atoms, they do not suffer fabrication spread and can have coherence times of seconds or longer.
State Preparation and Readout
Ions are initialized by optical pumping into a known state and read out by state-dependent fluorescence: a laser drives a cycling transition only if the ion is in one qubit state, so that state scatters many photons and appears bright while the other stays dark. A camera or photomultiplier collects the light, giving high-fidelity, nondestructive measurement of each ion.
Single- and Two-Qubit Control
- Single-qubit gates use resonant microwaves or a pair of laser beams driving a stimulated Raman transition.
- Two-qubit gates couple the internal states through the ions' shared motion in the trap.
- Individual addressing uses tightly focused laser beams or micro-fabricated electrodes to pick out one ion.
The Motional Bus
The defining feature of ion-trap hardware is that ions in a common trap share collective vibrational modes, like beads on a spring. State-dependent forces couple a qubit's internal state to this shared motion, and the motion carries the interaction to a second qubit. This motional bus lets any pair in a small register interact, giving all-to-all connectivity that superconducting arrays lack.
Scaling Architectures
Long chains become hard to control as more modes appear, so scaling relies on either shuttling ions between trap zones, the quantum charge-coupled device approach, or linking separate traps with photonic interconnects. The Molmer-Sorensen gate, described separately, is the standard entangling operation. Ion traps trade slower gate speeds and demanding laser systems for outstanding coherence and connectivity.