Abstract
This paper presents an overview of the Al+ optical clock, which is based on quantum logic spectroscopy
and provides the most accurate frequency measurement ever reported. Dehmelt’s original design of the
optical clock was not realized due to the difficulty in generating the vacuum ultraviolet radiation
necessary for laser cooling and the ion’s quantum state detection. The problem was solved by
sympathetically cooling the ion with another ion and detecting the quantum state using the ancillary ion.
The method, which is called quantum logic spectroscopy, comes from the use of phonon qubit as a bus
of the quantum state of the ions in the Cirac-Zoller ion-trap quantum computer. The clock can be
simplifi ed by introducing direct excitation by vacuum ultraviolet radiation or another ion species. The
clock’s stability will be improved more than ten times by a middle-term stabilized clock laser.
