Coherent control of fermion pair qubits

Coherent control of entangled fermion pairs can serve as a promising physical resource for quantum simulation and computation. Here we experimentally demonstrate a robust quantum register comprised of hundreds of fermionic atom pairs trapped in an optical lattice. The qubit consists of a protected subspace of vibrational states, with a stable energy splitting given by the atomic recoil energy. We observe coherence times on the scale of ten seconds. Via coherent conversion of free atom pairs into tightly bound molecules, we tune the two-fermion gate speed over three orders of magnitude, yielding ~10,000 gates within the coherence time. The methods presented here open the door towards fermion-based quantum computation and fully controlled generation of large-scale entangled many-body states.