Magnetic materials for finite-temperature quantum computing

The potential use of interacting magnetic nanodots for quantum computing (qubit) operations is investigated by model calculations. The quantum entanglement of the low-lying ferromagnetic states, as quantified by the concurrence, exhibits a resonant peak whose position and width depend on parameters such as dot anisotropy, interdot exchange, and external field gradient. The maximum operation temperature is proportional to the magnetocrystalline anisotropy of the dot material. A specific condition is that the dots are sufficiently small so that the interatomic exchange ensures a coherent magnetization state and quantum coherence at finite temperatures. From a material point of view, there is a quite rigid upper limit of about 100 K, but to avoid decoherence it will be necessary to sacrifice a substantial fraction of this temperature, probably at least one order of magnitude.