  We demonstrate experimentally a robust quantum memory using a
magnetic-field-independent hyperfine transition in 9Be+ atomic ion qubits at a
magnetic field B ~= 0.01194 T. We observe that the single physical qubit memory
coherence time is greater than 10 seconds, an improvement of approximately five
orders of magnitude from previous experiments with 9Be+. We also observe long
coherence times of decoherence-free subspace logical qubits comprising two
entangled physical qubits and discuss the merits of each type of qubit.
