Spin Dependent Forces and Entanglement of Atomic Qubits using Optical Frequency Combs*

The spectral purity and large bandwidth of pulsed lasers makes them attractive candidates for precision control of multi-level atomic systems. We use a train of off resonant picosecond pulses from a mode-locked laser to drive stimulated Raman transitions between the hyperfine levels ($\sim$10 GHz spacing) of trapped ytterbium ions and to cool to the quantum ground state of motion. By simultaneously addressing the spin and the motion of trapped ions using a train of laser pulses, we apply spin-dependent forces to create a single-ion Schrodinger cat state and implement a gate between two trapped ions to entangle their spins [1]. We also use high-intensity pulses to demonstrate fast ($<$10 ps) single qubit operations that can be used as the building blocks for fast multi-qubit entangling gates [2]. [1]. D. Hayes et al. arXiv:1001.2127v2 [2] Garc\'{i}a-Ripoll \textit{et al.}, PRL \textbf{91}, 157901 (2003). Duan, PRL \textbf{93}, 100502 (2004).