Many-body singlets by dynamic spin polarization

Abstract

We show that dynamic spin polarization by collective raising and lowering operators can drive a spin ensemble from arbitrary initial state to many-body singlets, the zero-collective-spin states with large-scale entanglement. For an ensemble of N arbitrary spins, both the variance of the collective spin and the number of unentangled spins can be reduced to O(1) [versus the typical value of O(N)], and in the steady state many-body singlets are occupied with a population of ∼20% independent of the ensemble size. We discuss a potential implementation in a mesoscopic ensemble of nuclear spins using dynamic nuclear spin polarization by an electron. The result is of twofold significance for spin quantum technology: (1) a cleaner surrounding and less quantum noise for the electron spin and (2) a resource of entanglement for nuclear-spin-based quantum information processing. The scheme can also be applied to other spin systems where collective raising and lowering operations are available. © 2011 American Physical Society.