In order to establish an applicable system for advanced quantum information processing based on the interaction between light and atoms, we have demonstrated a quantum nondemolition measurement with a collective spin of cold ytterbium atoms (${}^{171}\mathrm{Yb}$), and have observed ${1.8}_{-1.5}^{+2.4}\mathrm{dB}$ spin squeezing. Since ${}^{171}\mathrm{Yb}$ atoms have only a nuclear spin of one-half in the ground state, the system constitutes the simplest spin ensemble and is thus robust against decoherence. We used very short pulses with a width of 100 ns, and as a result the interaction time became much shorter than the decoherence time, which is important for multistep quantum information processing.

• Received 18 August 2008

DOI:https://doi.org/10.1103/PhysRevLett.102.033601