© Ion Storage Group, NIST.
The next generation of atomic clocks will operate at optical frequencies. Such clocks are in the laboratory stage now, but one can expect that they will become practical devices in the coming years. Two quite different approaches are employed, both based on laser-cooled particles. The first, shown here, employs a single trapped ion. This trap holds a second ion for support purposes, but the frequency reference is a single ion that is held in almost ideal conditions of isolation. The second approach employs a cloud of ultracold atoms held in an optical lattice, such as those shown in Figure 2 (Unit 5, Section 1). The clock has the disadvantage that the lattice can perturb the atoms, and the atoms can perturb each other. However, it has the advantage of providing large signals and operating continuously. At the moment, the two approaches are running almost neck-and-neck. (Unit: 5)