Single-atom interferometry

The phase shift of the hyperfine Larmor precession of an individual ground- state Yb-171(+) ion upon pulsed variation of the ambient magnetic field has been measured by microwave-optical double resonance interpreted in terms o f Mach-Zehnder interferometry, Averaging over an ensemble of individual mea surements, compared with measurements on an ensemble of ions, demonstrates quantum ergodicity. Even a single measurement yields (incomplete) phase inf ormation. Outside the peaks and dips of the interferogram, where ion probin g is incompatible with ion preparation, the results of measurements are sto chastic. This is demonstrated by laser exciting the ion on an E2 line.