title: Can a quantum nondemolition measurement improve the sensitivity of an atomic magnetometer?
abstract: We consider the limitations due to noise (e.g., quantum projection noise and photon shot-noise) on the sensitivity of an idealized atomic magnetometer that utilizes spin squeezing induced by a continuous quantum nondemolition measurement. Such a magnetometer measures spin precession of N atomic spins by detecting optical rotation of far-detuned light. We show that for very short measurement times, the optimal sensitivity scales as N(-3/4); if strongly squeezed probe light is used, the Heisenberg limit of N-1 scaling can be achieved. However, if the measurement time exceeds tau(rel)/N(1/2) in the former case, or tau(rel)/N in the latter, where tau(rel) is the spin relaxation time, the scaling becomes N(-1/2), as for a standard shot-noise-limited magnetometer.
authors.affiliation: Department of Physics, University of Latvia, 19 Rainis blvd, Riga, LV-1586, Latvia.
authors.forename: M
authors.initials: M
authors.lastname: Auzinsh
authors.forename: D
authors.initials: D
authors.lastname: Budker
authors.forename: D F
authors.initials: DF
authors.lastname: Kimball
authors.forename: S M
authors.initials: SM
authors.lastname: Rochester
authors.forename: J E
authors.initials: JE
authors.lastname: Stalnaker
authors.forename: A O
authors.initials: AO
authors.lastname: Sushkov
authors.forename: V V
authors.initials: VV
authors.lastname: Yashchuk