Cirac–Zoller controlled-NOT gate
The Cirac–Zoller CNOT gate is a way to perform a two-qubit operation using two trapped ions. Each qubit is stored in internal states of an ion (ground and excited), and the ions share a common vibrational motion that acts as a data bus. An extra state is available for the gate’s steps. The ions form a linear chain in a trap and are cooled to their motional ground state.
The gate uses red sideband laser pulses that couple the electronic states to the chain’s motion. In a three-pulse sequence, the joint state with both qubits in the excited state (ee) picks up a phase of -1, while the other three basis states stay unchanged. This is a controlled-Z (CZ) gate. To get a CNOT, a Hadamard gate is applied to the second qubit before and after the CZ operation.
The idea relies on the Jaynes–Cummings model, where the two-level system (g and e) interacts with a normal mode of the ion chain. To keep transitions from moving more than one quantum of motion, the system is operated in the Lamb–Dicke regime, which also makes the gate relatively slow.
The Cirac–Zoller gate was first demonstrated in 2003 at the University of Innsbruck with two calcium ions. It is a central part of the trapped-ion quantum-computer approach and, together with a few other gates, forms a universal set for performing any quantum computation.
This page was last edited on 2 February 2026, at 12:48 (CET).