Ultrafast Manipulation of Trapped Ion Qubits*

Ultrashort light pulses are an attractive tool for trapped ion quantum information processing. High pulse intensity permits far-detuned ($>$10 nm) operation, where decoherence from differential AC Stark shifts and spontaneous emission is suppressed. Short pulse duration allows interaction times shorter than a trap oscillation, circumventing the need for cooling to the Lamb-Dicke limit. We describe an experiment with trapped $^{171}$Yb$^+$ using a vanadate laser ($\sim$10 ps pulses at 355 nm). Since the single pulse bandwidth exceeds the $S_{1/2}$ hyperfine splitting, coherent Raman transitions between qubit states should be possible. This is in contrast to our previous work [1] with near-resonant pulses that coherently transfer population to the P-state. It should also be possible to use a series of multiple pulses to impart spin-dependent forces. By controlling the pulse timing and phase we could then entangle multiple ions in a temperature insensitive manner [2,3]. [1] Madsen \textit{et al.}, PRL \textbf{97}, 040505 (2006). [2] Garc\'{i}a-Ripoll \textit{et al.}, PRL \textbf{91}, 157901 (2003). [3] Duan, PRL \textbf{93}, 100502 (2004).