Engineering quantum pure states of a trapped cold ion beyond the Lamb-Dicke limit

Based on the conditional quantum dynamics of laser-ion interactions, we propose an efficient theoretical scheme to deterministically generate quantum pure states of a single trapped cold ion without performing the Lamb-Dicke approximation. An arbitrary quantum state can be created by sequentially using a series of classical laser pulses with selected frequencies, initial phases and durations. As special examples, we further show how to create or approximate several typical macroscopic quantum states, such as the phase state and the even/odd coherent states. Unlike previous schemes operating in the Lamb-Dicke regime, the present one does well for an arbitrary-strength coupling between the internal and external degrees of freedom of the ion. The experimental realizability of this approach is also discussed.

Figure 1

The $k$-dependent Rabi frequency ${\Omega }_{0,k}$ for different LD parameters: $\eta =0.202$ [5], 0.25 [12], 0.35, 0.5, and 0.9.