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 ${\mathrm{MnF}}_2$ and ${\mathrm{FeF}}_2$. 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 ${\mathrm{FeF}}_2$, are compared with earlier spontaneous Raman scattering measurements. The squeezing effect is observed to be at least one order of magnitude stronger in ${\mathrm{FeF}}_2$ than in ${\mathrm{MnF}}_2$.

• Received 20 February 2006

DOI:https://doi.org/10.1103/PhysRevB.73.184434