title: Purification of an unpolarized spin ensemble into entangled singlet pairs.
abstract: Dynamical polarization of nuclear spin ensembles is of central importance for magnetic resonance studies, precision sensing and for applications in quantum information theory. Here we propose a scheme to generate long-lived singlet pairs in an unpolarized nuclear spin ensemble which is dipolar coupled to the electron spins of a Nitrogen Vacancy center in diamond. The quantum mechanical back-action induced by frequent spin-selective readout of the NV centers allows the nuclear spins to pair up into maximally entangled singlet pairs. Counterintuitively, the robustness of the pair formation to dephasing noise improves with increasing size of the spin ensemble. We also show how the paired nuclear spin state allows for enhanced sensing capabilities of NV centers in diamond.
authors.affiliation: 3rd Institute of Physics, University of Stuttgart, Pfaffenwaldring 57, 70569, Stuttgart, Germany.
authors.forename: Johannes N
authors.initials: JN
authors.lastname: Greiner
authors.affiliation: 3rd Institute of Physics, University of Stuttgart, Pfaffenwaldring 57, 70569, Stuttgart, Germany. d.dasari@physik.uni-stuttgart.de.|Max Planck Institute for Solid State Research, Heisenbergstraße 1, 70569, Stuttgart, Germany. d.dasari@physik.uni-stuttgart.de.
authors.forename: Durga Bhaktavatsala Rao
authors.initials: DBR
authors.lastname: Dasari
authors.affiliation: 3rd Institute of Physics, University of Stuttgart, Pfaffenwaldring 57, 70569, Stuttgart, Germany.|Max Planck Institute for Solid State Research, Heisenbergstraße 1, 70569, Stuttgart, Germany.
authors.forename: Jörg
authors.initials: J
authors.lastname: Wrachtrup