Ground-state and non-ground-state Bose-Einstein condensation of magnons in superfluid 3He-B

Long-lived coherent spin precession of 3He-B at low temperatures around 0.20 Tc is interpreted as Bose-Einstein condensation of spin-wave excitations or magnons in a magnetic trap formed by the order parameter texture. The harmonic spectrum of energy levels and their nonlinear hysteretic population characteristics is obtained from cw NMR measurements with the condensate droplet embedded in the center of the cylindrically symmetric flare-out texture in a rotating cryostat. Any state can be populated and sustained by continuous rf pumping at its specific excitation frequency. At large pumping a Q-ball state is formed which can be described as a bosonic analog of the electron bubble in helium liquids. On switching off the pumping, magnons from an excited level drop to the ground state with a decay time which is several times faster than that of the ground state.