A decoherence-free quantum memory using trapped ions

We demonstrate a decoherence-free quantum memory of one qubit. By encoding the qubit into the decoherence-free subspace (DFS) of a pair of trapped 9Be (+) ions, we protect the qubit from environment-induced dephasing that limi ts the storage time of a qubit composed of a single ion. We measured the st orage time under ambient conditions and under interaction with an engineere d noisy environment and observed that encoding into the DFS increases the s torage time by up to an order of magnitude. The encoding reversibly transfe rs an arbitrary qubit stored in a single ion to the DFS of two ions.