Spin squeezing in atomic systems

Summary form only given. In high-precision atomic experiments such as atomic interferometry, the accuracy is ultimately limited by the so-called quantum projection noise, due to the fact that the atoms are not in an eigenstate of the measured quantity. In an ensemble of N independent atoms, fluctuations proportional to N/sup -1/2/ result from this effect. A few years ago, it was shown that using squeezed atomic states would allow to reduce these fluctuations, in the same way as squeezed states of light allow to obtain noise reduction in measurements of the electromagnetic field.