Single-shot read-out of an individual electron spin in a quantum dot

Spin is a fundamental property of all elementary particles. Classically it can be viewed as a tiny magnetic moment, but a measurement of an electron spin along the direction of an external magnetic field can have only two outcomes(1): parallel or anti-parallel to the field. This discreteness reflects the quantum mechanical nature of spin. Ensembles of many spins have found diverse applications ranging from magnetic resonance imaging(2) to magneto-electronic devices(3), while individual spins are considered as carriers for quantum information. Read-out of single spin states has been achieved using optical techniques(4), and is within reach of magnetic resonance force microscopy(5). However, electrical read-out of single spins(6-13) has so far remained elusive. Here we demonstrate electrical single-shot measurement of the state of an individual electron spin in a semiconductor quantum dot(14). We use spin-to-charge conversion of a single electron confined in the dot, and detect the single-electron charge using a quantum point contact; the spin measurement visibility is similar to65%. Furthermore, we observe very long single-spin energy relaxation times (up to similar to0.85 ms at a magnetic field of 8 T), which are encouraging for the use of electron spins as carriers of quantum information.