We propose a scheme to generate number states, and specific superpositions of them, of the vibrational motion of a trapped ion via laser excitation of two vibronic transitions. Without detrimental effects on the internal state preparation, the ion can be initially in thermal motion and undergo spontaneous emission. In particular, qubits that are robust against noise $(\alpha |0〉+\beta |1〉$ states) can be generated with arbitrary amplitudes.

• Received 17 September 1999

DOI:https://doi.org/10.1103/PhysRevA.61.025401