Nondestructive detection of atom counts in laser-trapped ¹⁷¹Yb atoms

We present the experimental demonstration of nondestructive detection of ¹⁷¹Yb atoms in a magneto-optical trap (MOT) based on phase shift measurement induced by the atoms on a weak off-resonant laser beam. After loading a green MOT of ¹⁷¹Yb atoms, the phase shift is obtained with a two-color Mach–Zehnder interferometer by means of ±45 MHz detuning with respect to the ¹S₀–¹P₁ transition. We measured a phase shift of about 100 mrad corresponding to an atom count of around 5 × 10⁵. This demonstrates that it is possible to obtain the number of atoms without direct destructive measurement compared with the absorption imaging method. This scheme could be an important approach towards a high-precision lattice clock for clock operation through suppression of the impact of the Dick effect.