title: Stroboscopic backaction evasion in a dense alkali-metal vapor.
abstract: We explore experimentally quantum nondemolition measurements of atomic spin in a hot potassium vapor in the presence of spin-exchange relaxation. We demonstrate a new technique for backaction evasion by stroboscopic modulation of the probe light. With this technique we study spin noise as a function of polarization for atoms with spin greater than 1/2 and obtain good agreement with a simple theoretical model. We point that, in a system with fast spin exchange, where the spin-relaxation rate is changing with time, it is possible to improve the long-term sensitivity of atomic magnetometry by using quantum nondemolition measurements.
authors.affiliation: Department of Physics, Princeton University, Princeton, New Jersey 08544, USA.
authors.forename: G
authors.initials: G
authors.lastname: Vasilakis
authors.forename: V
authors.initials: V
authors.lastname: Shah
authors.forename: M V
authors.initials: MV
authors.lastname: Romalis