title: Coherent storage of microwave excitations in rare-earth nuclear spins.
abstract: Interfacing between various elements of a computer--from memory to processors to long range communication--will be as critical for quantum computers as it is for classical computers today. Paramagnetic rare-earth doped crystals, such as Nd(3+):Y2SiO5(YSO), are excellent candidates for such a quantum interface: they are known to exhibit long optical coherence lifetimes (for communication via optical photons), possess a nuclear spin (memory), and have in addition an electron spin that can offer hybrid coupling with superconducting qubits (processing). Here we study two of these three elements, demonstrating coherent storage and retrieval between electron and (145)Nd nuclear spin states in Nd(3+):YSO. We find nuclear spin coherence times can reach 9 ms at ∼5  K, about 2 orders of magnitude longer than the electron spin coherence, while quantum state and process tomography of the storage or retrieval operation between the electron and nuclear spin reveal an average state fidelity of 0.86. The times and fidelities are expected to further improve at lower temperatures and with more homogeneous radio-frequency excitation.
authors.affiliation: London Centre for Nanotechnology, University College London, London WC1H 0AH, United Kingdom.|Department of Materials, Oxford University, Oxford OX1 3PH, United Kingdom.
authors.forename: Gary
authors.initials: G
authors.lastname: Wolfowicz
authors.affiliation: London Centre for Nanotechnology, University College London, London WC1H 0AH, United Kingdom.
authors.forename: Hannes
authors.initials: H
authors.lastname: Maier-Flaig
authors.affiliation: PSL Research University, Chimie ParisTech-CNRS, Institut de Recherche de Chimie Paris, 75005, Paris, France.|LASIR CNRS UMR 8516, Université de Lille, France.
authors.forename: Robert
authors.initials: R
authors.lastname: Marino
authors.affiliation: PSL Research University, Chimie ParisTech-CNRS, Institut de Recherche de Chimie Paris, 75005, Paris, France.|Sorbonne Universités, UPMC Univ Paris 06, 75005, Paris, France.
authors.forename: Alban
authors.initials: A
authors.lastname: Ferrier
authors.affiliation: LASIR CNRS UMR 8516, Université de Lille, France.
authors.forename: Hervé
authors.initials: H
authors.lastname: Vezin
authors.affiliation: London Centre for Nanotechnology, University College London, London WC1H 0AH, United Kingdom.|Department of Electronic and Electrical Engineering, UCL, London WC1E 7JE, United Kingdom.
authors.forename: John J L
authors.initials: JJ
authors.lastname: Morton
authors.affiliation: PSL Research University, Chimie ParisTech-CNRS, Institut de Recherche de Chimie Paris, 75005, Paris, France.
authors.forename: Philippe
authors.initials: P
authors.lastname: Goldner