We demonstrate nondestructive (lossless) fluorescent state detection of individual neutral atom qubits trapped in an optical lattice. The hyperfine state of the atom is measured with a 95% accuracy and an atom loss rate of 1%. Individual atoms are initialized and detected over 100 times before being lost from the trap, representing a 100-fold improvement in data collection rates over previous experiments. Microwave Rabi oscillations are observed with repeated measurements of one and the same single atom.
We introduce lossless state detection of trapped neutral atoms based on cavity-enhanced fluorescence. In an experiment with a single 87Rb atom, a hyperfine-state-detection fidelity of 99.4% is achieved in 85 μs. The quantum bit is interrogated many hundreds of times without loss of the atom while a result is obtained in every readout attempt. The fidelity proves robust against atomic frequency shifts induced by the trapping potential. Our scheme does not require strong coupling between the atom and cavity and can be generalized to other systems with an optically accessible quantum bit.