Spin Squeezing of a Cold Atomic Ensemble with the Nuclear Spin of One-Half

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 (Yb171), and have observed 1.8_-1.5^+2.4dB spin squeezing. Since Yb171 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.