We demonstrate the parallel and nondestructive readout of the hyperfine state for optically trapped ^{87}Rb atoms. The scheme is based on state-selective fluorescence imaging and achieves detection fidelities >98% within 10 ms, while keeping 99% of the atoms trapped. For the readout of dense arrays of neutral atoms in optical lattices, where the fluorescence images of neighboring atoms overlap, we apply a novel image analysis technique using Bayesian inference to determine the internal state of multiple atoms. Our method is scalable to large neutral atom registers relevant for future quantum information processing tasks requiring fast and nondestructive readout and can also be used for the simultaneous readout of quantum information stored in internal qubit states and in the atoms' positions.
We achieve fast, nondestructive quantum-state readout via fluorescence detection of a single
87Rb atom in the
5S1/2 (F=2) ground state held in an optical dipole trap. The atom is driven by linearly polarized readout laser beams, making the scheme insensitive to the distribution of atomic population in magnetic sublevels. We demonstrate a readout fidelity of $97.6\ifmmode\pm\else\textpm\fi{}0.2%$ in a readout time of $160\ifmmode\pm\else\textpm\fi{}20\phantom{\rule{4pt}{0ex}}\ensuremath{\mu}\mathrm{s}$ with the atom retained in
>97 of the trials, representing an advancement over other magnetic-state-insensitive techniques. We demonstrate that the
F=2 state is partially protected from optical pumping by the distribution of the dipole matrix elements for the various transitions and the ac-Stark shifts from the optical trap. Our results are likely to find application in neutral-atom quantum computing and simulation.