title: Nondemolition measurements of a single quantum spin using Josephson oscillations.
abstract: We consider a single localized spin-1/2 between the singlet superconducting leads of a Josephson junction (e.g., a superconducting STM). For the spin subject to a dc magnetic field B parallel z, we study the spin dynamics and the possibility to measure the spin state via transport through the junction embedded in a dissipative circuit. Turning on the tunneling or a voltage bias induces oscillations of the Josephson current, with an amplitude sensitive to the initial value of the z component of the spin, S(z)=+/-1/2. At low temperatures, when effects of quasiparticles are negligible, this procedure realizes a quantum nondemolition measurement of S(z).
authors.affiliation: Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
authors.forename: L
authors.initials: L
authors.lastname: Bulaevskii
authors.forename: M
authors.initials: M
authors.lastname: Hruska
authors.forename: A
authors.initials: A
authors.lastname: Shnirman
authors.forename: D
authors.initials: D
authors.lastname: Smith
authors.forename: Yu
authors.initials: Y
authors.lastname: Makhlin