  Extremely fast qubit controls can greatly reduce the calculation time in
quantum computation, and potentially resolve the finite-time decoherence issues
in many physical systems. Here, we propose and experimentally demonstrate
pico-second time-scale controls of atomic clock state qubits, using Berry-phase
gates implemented with a pair of chirped laser pulses. While conventional
methods of microwave or Raman transitions do not allow atomic qubit controls
within a time faster than the hyperfine free evolution period, our approach of
ultrafast Berry-phase gates accomplishes fast clock-state operations. We also
achieves operational robustness against laser parametric noises, since
geometric phases are determined by adiabatic evolution pathway only, without
being affected by any dynamic details. The experimental implementation is
conducted with two linearly polarized, chirped ultrafast optical pulses,
interacting with five single rubidium atoms in an array of optical tweezer
dipole traps, to demonstrate the proposed ultrafast clock-state gates and their
operational robustness.
