Trapped Ions Make Impeccable Qubits

The realization, two decades ago, that quantum mechanics can be a powerful resource to speed up important computational tasks [1] led to intense research efforts to find adequate physical systems for quantum computation. One of the hurdles to a viable technology is the requirement to prepare, manipulate, and measure quantum bits (qubits) with near perfect accuracy: Imperfect control leads to errors that can accumulate over the computation process. Techniques like quantum error correction and fault-tolerant designs can, in principle, overcome these errors. But these strategies can be successful only if the error probabilities are lower than a threshold value. They also increase the complexity of the required quantum hardware, since they require additional qubits. Recent calculations [2] suggest that an error probability of less than 1% would enable fault-tolerant codes, and that lower error probabilities dramatically decrease the number of qubits required for such codes.