Nondemolition measurements of a single quantum spin using Josephson oscillations.
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).
Bulaevskii
L
L
Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
Hruska
M
M
Shnirman
A
A
Smith
D
D
Makhlin
Yu
Y