We propose and implement a non-destructive measurement that distinguishes between two-electron spin states in a quantum dot. In contrast to earlier experiments with quantum dots, the spins are left behind in the state corresponding to the measurement outcome. By measuring the spin states twice within a time shorter than the relaxation time, T1, correlations between consecutive measurements are observed. They disappear as the wait time between measurements become comparable to T1. The correlation between the post-measurement state and the measurement outcome is measured to be ~90% on average.
@article{arxiv.cond-mat/0603794,
title = {Non-destructive measurement of electron spins in a quantum dot},
author = {T. Meunier and I. T. Vink and L. H. Willems van Beveren and F. H. L. Koppens and H. P. Tranitz and W. Wegscheider and L. P. Kouwenhoven and L. M. K. Vandersypen},
journal= {arXiv preprint arXiv:cond-mat/0603794},
year = {2009}
}