title: Spin squeezing of atomic ensembles via nuclear-electronic spin entanglement.
abstract: We demonstrate spin squeezing in a room temperature ensemble of approximately 10(12) cesium atoms using their internal structure, where the necessary entanglement is created between nuclear and electronic spins of each individual atom. This state provides improvement in measurement sensitivity beyond the standard quantum limit for quantum memory experiments and applications in quantum metrology and is thus a complementary alternative to spin squeezing obtained via interatom entanglement. Squeezing of the collective spin is verified by quantum state tomography.
authors.affiliation: QUANTOP, Danish National Research Foundation Center for Quantum Optics, Niels Bohr Institute, Copenhagen University, DK 2100, Denmark.
authors.forename: T
authors.initials: T
authors.lastname: Fernholz
authors.forename: H
authors.initials: H
authors.lastname: Krauter
authors.forename: K
authors.initials: K
authors.lastname: Jensen
authors.forename: J F
authors.initials: JF
authors.lastname: Sherson
authors.forename: A S
authors.initials: AS
authors.lastname: Sørensen
authors.forename: E S
authors.initials: ES
authors.lastname: Polzik