Impulsive Spin-Motion Entanglement for Fast Quantum Computation and Sensing

We perform entanglement of spin and motional degrees of freedom of a single, ground-state trapped ion through the application of a $16$ ps laser pulse. The duration of the interaction is significantly shorter than both the motional timescale ($30$ $\mu$s) and spin precession timescale ($1$ ns) , demonstrating that neither sets a fundamental speed limit on this operation for quantum information processing. Entanglement is demonstrated through the collapse and revival of spin coherence as the spin components of the wavefunction separate and recombine in phase space. We infer the fidelity of these single qubit operations to be $(97_{-4}^{+3})\mathrm{\%}$.