Magnon squeezing in antiferromagnetic MnF_2 and FeF_2

摘要

Quantum squeezing of a collective spin-wave excitation or magnon using femtosecond optical pulses has been used to generate correlated pairs of spins with equal and opposite wave vectors in antiferromagnetic MnF_2 and FeF_2. In the squeezed state, the fluctuations of the magnetization of a crystallographic unit cell vary periodically in time and are reduced below that of the ground state quantum noise. The results obtained, including their temperature dependence for FeF_2, are compared with earlier spontaneous Raman scattering measurements. The squeezing effect is observed to be at least one order of magnitude stronger in FeF_2 than in MnF_2.