Nondemolition Measurements of a Single Quantum Spin using Josephson Oscillations
Lev N. Bulaevskii, Marina Hruška, Alexander Shnirman, Darryl Lyle Smith, Yu. Makhlin · Physical Review Letters · 2004
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).