Limits on partition noise from the heating rate of vibrational phonons in radio-frequency quadrupole traps

The heating rate of ions laser cooled to the vibrational ground state of an rf quadrupole trap provide sensitive limits on partition noise (shot noise) of the rf current in the trap electrodes. The millisecond lifetimes observed in recent experiments correspond to a partition noise power spectral density (Fano factor) less than [Formula Presented] of the Poisson value, showing a sensitivity [Formula Presented] greater than the solid-state measurements. © 2002 The American Physical Society.